Document and Entity Information - USD ($) $ in Millions	12 Months Ended
Document and Entity Information - USD ($) $ in Millions	Dec. 31, 2017	Mar. 14, 2018	Jun. 30, 2017
Document And Entity Information [Abstract]
Entity Registrant Name	T2 Biosystems, Inc.
Entity Central Index Key	0001492674
Document Type	10-K
Document Period End Date	Dec. 31, 2017
Trading Symbol	TTOO
Amendment Flag	false
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Filer Category	Accelerated Filer
Entity Public Float			$ 58.6
Entity Common Stock, Shares Outstanding		36,019,800
Document Fiscal Year Focus	2017
Document Fiscal Period Focus	FY

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Current assets:
Cash and cash equivalents	$ 41,799	$ 73,488
Accounts receivable	467	327
Prepaid expenses and other current assets	708	820
Inventories	1,344	803
Total current assets	44,318	75,438
Property and equipment, net	10,015	13,589
Restricted cash	260	260
Other assets	268	281
Total assets	54,861	89,568
Current liabilities:
Accounts payable	648	962
Accrued expenses and other current liabilities	6,218	4,908
Derivative liability	2,238
Notes payable	40,696	1,269
Deferred revenue	1,736	2,445
Current portion of lease incentives	246	301
Total current liabilities	51,782	9,885
Notes payable, net of current portion	1,008	39,504
Lease incentives, net of current portion	731	792
Other liabilities		49
Commitments and contingencies (see Note 12)
Stockholders’ equity:
Preferred stock, $0.001 par value; 10,000,000 shares authorized; no shares issued and outstanding
Common stock, $0.001 par value; 200,000,000 shares authorized; 35,948,900 and 30,482,712 shares issued and outstanding at December 31, 2017 and December 31, 2016, respectively	36	30
Additional paid-in capital	267,421	242,997
Accumulated deficit	(266,117)	(203,689)
Total stockholders’ equity	1,340	39,338
Total liabilities and stockholders’ equity	$ 54,861	$ 89,568

Consolidated Balance Sheet (Parentheticals) - $ / shares	Dec. 31, 2017	Dec. 31, 2016
Statement Of Financial Position [Abstract]
Preferred stock, par value (in dollars per share)	$ 0.001	$ 0.001
Preferred stock, shares authorized	10,000,000	10,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value (in dollars per share)	$ 0.001	$ 0.001
Common stock, shares authorized	200,000,000	200,000,000
Common stock, shares issued	35,948,900	30,482,712
Common stock, shares outstanding	35,948,900	30,482,712

Consolidated Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Revenue:
Product revenue	$ 3,440	$ 1,747	$ 599
Research revenue	1,226	2,333	2,214
Total revenue	4,666	4,080	2,813
Costs and expenses:
Cost of product revenue	12,028	6,872	1,740
Research and development	23,733	24,009	25,362
Selling, general and administrative	22,757	24,077	19,094
Total costs and expenses	58,518	54,958	46,196
Loss from operations	(53,852)	(50,878)	(43,383)
Interest expense, net	(8,907)	(4,098)	(1,967)
Other income, net	331	172	60
Net loss and comprehensive loss	$ (62,428)	$ (54,804)	$ (45,290)
Net loss per share — basic and diluted	$ (1.94)	$ (2.11)	$ (2.21)
Weighted-average number of common shares used in computing net loss per share — basic and diluted	32,131,512	26,015,751	20,501,748

Consolidated Statements Stockholders' Equity - USD ($) $ in Thousands	Total	Common Stock [Member]	Additional Paid-in Capital [Member]	Accumulated Deficit [Member]
Balance at Dec. 31, 2014	$ 53,001	$ 20	$ 156,576	$ (103,595)
Balance (in shares) at Dec. 31, 2014		20,041,645
Stock-based compensation expense	4,168		4,168
Issuance of common stock	33,256	$ 4	33,252
Issuance of common stock (in shares)		3,691,049
Issuance of common stock from exercise of stock options and employee stock purchase plan	1,804		1,804
Issuance of common stock from exercises of stock options and employee stock purchase plan (in shares)		442,687
Net loss	(45,290)			(45,290)
Balance at Dec. 31, 2015	46,939	$ 24	195,800	(148,885)
Balance (in shares) at Dec. 31, 2015		24,175,381
Stock-based compensation expense	4,848		4,848
Offering costs on issuance of common stock from secondary public offering	(215)		(215)
Issuance of common stock	39,723	$ 6	39,717
Issuance of common stock (in shares)		6,055,341
Issuance of common stock from exercise of stock options and employee stock purchase plan	1,018		1,018
Issuance of common stock from exercises of stock options and employee stock purchase plan (in shares)		251,990
Issuance of warrants	1,829		1,829
Net loss	(54,804)			(54,804)
Balance at Dec. 31, 2016	$ 39,338	$ 30	242,997	(203,689)
Balance (in shares) at Dec. 31, 2016	30,482,712	30,482,712
Stock-based compensation expense	$ 4,790		4,790
Issuance of common stock	18,581	$ 5	18,576
Issuance of common stock (in shares)		5,031,250
Issuance of common stock from exercise of stock options and employee stock purchase plan	1,059	$ 1	1,058
Issuance of common stock from exercises of stock options and employee stock purchase plan (in shares)		434,938
Net loss	(62,428)			(62,428)
Balance at Dec. 31, 2017	$ 1,340	$ 36	$ 267,421	$ (266,117)
Balance (in shares) at Dec. 31, 2017	35,948,900	35,948,900

Consolidated Statement of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Operating activities
Net loss	$ (62,428)	$ (54,804)	$ (45,290)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	2,940	2,280	1,465
Stock-based compensation expense	4,790	4,848	4,168
Noncash interest expense	2,710	564	354
Loss on extinguishment of debt		112
Impairment of T2 owned instruments and components	2,571
Change in fair value of derivative instrument	2,238
Deferred rent	(115)	(250)	(119)
Changes in operating assets and liabilities:
Accounts receivable	(140)	42	(168)
Prepaid expenses and other assets	125	68	190
Inventories, net	(110)	(120)	(568)
Accounts payable	(314)	(61)	177
Accrued expenses and other liabilities	724	580	260
Deferred revenue	(709)	299	2,066
Net cash used in operating activities	(47,718)	(46,442)	(37,465)
Investing activities
Purchases and manufacture of property and equipment	(2,476)	(5,487)	(7,974)
Decrease in restricted cash			80
Net cash used in investing activities	(2,476)	(5,487)	(7,894)
Financing activities
Proceeds from issuance of common stock in public offering, net of offering costs	18,640	(385)	33,677
Proceeds from issuance of common stock and stock options exercises, net	1,059	1,018	1,804
Proceeds from private investment in public equity		39,723
Proceeds from notes payable, net of issuance costs		43,803	10,000
Repayments of note payable	(1,194)	(32,404)	(309)
Net cash provided by financing activities	18,505	51,755	45,172
Net decrease in cash and cash equivalents	(31,689)	(174)	(187)
Cash and cash equivalents at beginning of period	73,488	73,662	73,849
Cash and cash equivalents at end of period	41,799	73,488	73,662
Supplemental disclosures of cash flow information
Cash paid for interest	3,959	2,732	1,506
Supplemental disclosures of noncash activities
Accrued property and equipment	189	$ 82	247
Transfer from T2 owned equipment to inventory	431
Leasehold improvements paid by landlord			1,268
Transfer from other liabilities to accrued expenses and other current liabilities	585
Public offering costs unpaid at year end	$ 59		$ 420

Nature of Business	12 Months Ended
Nature of Business	Dec. 31, 2017
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Nature of Business	1. Nature of Business T2 Biosystems, Inc. (the “Company”) was incorporated on April 27, 2006 as a Delaware corporation with operations based in Lexington, Massachusetts. The Company is an in vitro diagnostics company that has developed an innovative and proprietary technology platform that offers a rapid, sensitive and simple alternative to existing diagnostic methodologies. The Company is using its T2 Magnetic Resonance technology, or T2MR, to develop a broad set of applications aimed at lowering mortality rates, improving patient outcomes and reducing the cost of healthcare by helping medical professionals make targeted treatment decisions earlier. T2MR enables rapid detection of pathogens, biomarkers and other abnormalities in a variety of unpurified patient sample types, including whole blood, plasma, serum, saliva, sputum and urine, and can detect cellular targets at limits of detection as low as one colony forming unit per milliliter, or CFU/mL. The Company’s initial development efforts target sepsis and Lyme disease, which are areas of significant unmet medical need in which existing therapies could be more effective with improved diagnostics. On September 22, 2014, the Company received market clearance from the U.S. Food and Drug Administration (“FDA”) for its first two products, the T2Dx Instrument (the “T2Dx”) and T2Candida Panel (“T2Candida”). On June 30, 2017, the Company received a CE Mark for its T2Bacteria Panel (“T2Bacteria”). On September 8, 2017, the Company filed a 510(k) premarket submission for the T2Bacteria Panel with the U.S. Food and Drug Administration (FDA). The Company has devoted substantially all of its efforts to research and development, business planning, recruiting management and technical staff, acquiring operating assets, raising capital, and, most recently, the commercialization and improvement of its existing products. Liquidity and Going Concern At December 31, 2017, the Company has cash and cash equivalents of $41.8 million and an accumulated deficit of $266.1 million. The future success of the Company is dependent on its ability to successfully commercialize its products, obtain regulatory clearance for and successfully launch its future product candidates, obtain additional capital and ultimately attain profitable operations. Historically, the Company has funded its operations primarily through its August 2014 initial public offering, its December 2015 confidentially marketed public offering (“CMPO”), its September 2016 private investment in public equity (“PIPE”) financing, its September 2017 CMPO, private placements of redeemable convertible preferred stock and debt financing arrangements. The Company is subject to a number of risks similar to other newly commercial life science companies, including, but not limited to commercially launching the Company’s products, development and market acceptance of the Company’s product candidates, development by its competitors of new technological innovations, protection of proprietary technology, and raising additional capital. Having obtained clearance from the FDA and a CE mark in Europe to market the T2Dx and T2Candida, the Company has incurred significant commercialization expenses related to product sales, marketing, manufacturing and distribution. In addition, the Company anticipates costs and expenses to increase as the Company continues to develop other product candidates, improve existing products and maintain, expand and protect its intellectual property portfolio. The Company may seek to fund its operations through public equity or private equity or debt financings, as well as other sources. However, the Company may be unable to raise additional funds or enter into such other arrangements when needed on favorable terms or at all. The Company’s failure to raise capital or enter into such other arrangements if and when needed would have a negative impact on the Company’s business, results of operations and financial condition and the Company’s ability to develop and commercialize T2Dx, T2Candida, T2Bacteria, and other product candidates. Pursuant to the requirements of Accounting Standards Codification (ASC) 205-40, Disclosure of Uncertainties about an Entity’s Ability to Continue as a Going Concern, management must evaluate whether there are conditions or events, considered in the aggregate, that raise substantial doubt about the Company’s ability to continue as a going concern within one year after the date that the financial statements are issued. This evaluation initially does not take into consideration the potential mitigating effect of management’s plans that have not been fully implemented as of the date the financial statements are issued. When substantial doubt exists under this methodology, management evaluates whether the mitigating effect of its plans sufficiently alleviates substantial doubt about the Company’s ability to continue as a going concern. The mitigating effect of management’s plans, however, is only considered if both (1) it is probable that the plans will be effectively implemented within one year after the date that the financial statements are issued, and (2) it is probable that the plans, when implemented, will mitigate the relevant conditions or events that raise substantial doubt about the entity’s ability to continue as a going concern within one year after the date that the financial statements are issued. Management believes that its existing cash and cash equivalents at December 31, 2017, together with funding available under the Term Loan Agreement, will be sufficient to allow the Company to fund its current operating plan through March 2019. However, as certain elements of the Company’s operating plan are outside of the Company’s control, including the approval of the Company’s T2Bacteria Panel and receipt of certain development and regulatory milestone payments under the Company’s Co-Development agreements, they cannot be considered probable. Under ASC 205-40, the future receipt of potential funding from the Company’s Co-Development partners and other resources cannot be considered probable at this time because none of the plans are entirely within the Company’s control. In addition, the Company is required to maintain a minimum cash balance under its Term Loan Agreement with CRG Servicing LLC (“CRG”) (Note 6). These conditions raise substantial doubt regarding the Company’s ability to continue as a going concern for a period of one year after the date that the financial statements are issued. Management's plans to alleviate the conditions that raise substantial doubt include raising additional funding, earning milestone payments pursuant the Company’s Co- Development agreements, delaying certain research projects and capital expenditures and eliminating certain future operating expenses in order to fund operations at reduced levels for the Company to continue as a going concern for a period of 12 months from the date the financial statements are issued. Management has concluded the likelihood that its plan to obtain sufficient funding from one or more of these sources or adequately reduce expenditures will be successful, while reasonably possible, is less than probable. Accordingly, the Company has concluded that substantial doubt exists about the Company’s ability to continue as a going concern for a period of at least twelve months from the date of issuance of these consolidated financial statements. The accompanying financial statements have been prepared on a going concern basis, which contemplates the realization of assets and satisfaction of liabilities in the ordinary course of business. The financial statements do not include any adjustments relating to the recoverability and classification of recorded asset amounts or the amounts and classification of liabilities that might result from the outcome of the uncertainties described above.

Summary of Significant Accounting Policies

12 Months Ended

Dec. 31, 2017

Accounting Policies [Abstract]

Summary of Significant Accounting Policies

2. Summary of Significant Accounting Policies

Basis of Presentation and Consolidation

The Company’s financial statements have been prepared in conformity with generally accepted accounting principles in the United States of America (“GAAP”). Any reference in these notes to applicable guidance is meant to refer to the authoritative United States generally accepted accounting principles as found in the Accounting Standards Codification (“ASC”) and Accounting Standards Updates (“ASU”) of the Financial Accounting Standards Board (“FASB”). The Company’s consolidated financial statements include the accounts of the Company and its wholly-owned subsidiary, T2 Biosystems Securities Corporation. All intercompany balances and transactions have been eliminated.

Use of Estimates

The preparation of the Company’s consolidated financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the amounts reported in the consolidated financial statements and accompanying notes. The Company utilizes certain estimates in the determination of the fair value of its stock options, deferred tax valuation allowances, revenue recognition, to record expenses relating to research and development contracts, accrued expenses, the fair value of a derivative liability and to classify the value of instrument raw material and work-in-process inventory between inventory and property and equipment. The Company bases its estimates on historical experience and other market‑specific or other relevant assumptions that it believes to be reasonable under the circumstances. Actual results could differ from such estimates.

Segment Information

Operating segments are defined as components of an enterprise about which separate discrete information is available for evaluation by the chief operating decision maker, or decision‑making group, in deciding how to allocate resources and in assessing performance. The Company’s chief operating decision maker is the Chief Executive Officer. The Company views its operations and manages its business in one operating segment, which is the business of developing and, upon regulatory clearance, launching commercially its diagnostic products aimed at lowering mortality rates, improving patient outcomes and reducing the cost of healthcare by helping medical professionals make targeted treatment decisions earlier.

Off‑Balance Sheet Risk and Concentrations of Credit Risk

The Company has no significant off-balance sheet risks, such as foreign exchange contracts, option contracts, or other foreign hedging arrangements. Cash and cash equivalents are financial instruments that potentially subject the Company to concentrations of credit risk. At December 31, 2017 and 2016, substantially all of the Company’s cash was deposited in accounts at one financial institution, with a significant amount invested in money market funds that are invested in short-term U.S. government agency securities. The Company maintains its cash deposits, which at times may exceed the federally insured limits, with a large financial institution and, accordingly, the Company believes such funds are subject to minimal credit risk.

For the year ended December 31, 2017, the Company derived approximately 19% of its total revenue from one customer and 10% of its total revenue from a second customer. For the year ended December 31, 2016, the Company derived approximately 45% of its total revenue from one customer and 10% of its total revenue from a second customer. For the year ended December 31, 2015, the Company derived approximately 50% of its total revenue from one customer and 25% of its total revenue from a second customer.

Cash Equivalents

Cash equivalents include all highly liquid investments maturing within 90 days from the date of purchase. Cash equivalents consist of money market funds invested in short-term U.S. government agency securities as of December 31, 2017 and 2016.

Accounts Receivable

The Company’s accounts receivable consists of amounts due from commercial customers and from research and development arrangements with partners. At each reporting period, management reviews all outstanding balances to determine if the facts and circumstances of each customer relationship indicate the need for a reserve. The Company does not require collateral and did not have an allowance for doubtful accounts at December 31, 2017 or 2016.

Inventories

Inventories are stated at the lower of cost or net realizable value. The Company determines the cost of its inventories, which includes amounts related to materials, direct labor, and manufacturing overhead, on a first-in, first-out basis. The Company performs an assessment of the recoverability of capitalized inventory during each reporting period, and writes down any excess and obsolete inventories to their realizable value in the period in which the impairment is first identified. Shipping and handling costs incurred for inventory purchases are capitalized and recorded upon sale in cost of product revenues in the consolidated statements of operations and comprehensive loss or are included in the value of T2-owned instruments and components, a component of property and equipment, net, and depreciated.

The Company capitalizes inventories in preparation for sales of products when the related product candidates are considered to have a high likelihood of regulatory clearance, which for the T2Dx Instrument and T2Candida Panel was upon the achievement of regulatory clearance, and the related costs are expected to be recoverable through sales of the inventories. In addition, the Company capitalizes inventories related to the manufacture of instruments that have a high likelihood of regulatory clearance, which for the T2Dx Instrument was upon the achievement of regulatory clearance, and will be retained as the Company’s assets, upon determination that the instrument has alternative future uses. In determining whether or not to capitalize such inventories, the Company evaluates, among other factors, information regarding the product candidate’s status of regulatory submissions and communications with regulatory authorities, the outlook for commercial sales and alternative future uses of the product candidate. Costs associated with development products prior to satisfying the inventory capitalization criteria are charged to research and development expense as incurred.

The Company classifies instruments that are Company-owned, as a component of property and equipment. Raw material and work-in-process inventories that are expected to be used to produce Company-owned instruments, based on our business model and forecast, are also classified as property and equipment. Company-owned instruments are instruments that are manufactured and placed with customers in connection with reagent rental agreements, or are used for internal purposes.

The components of inventory consist of the following (in thousands):

	December 31,		December 31,
	2017		2016
Raw materials	$	539	$	389
Work-in-process		562		351
Finished goods		243		63
Total inventories, net	$	1,344	$	803

Fair Value Measurements

The Company is required to disclose information on all assets and liabilities reported at fair value that enables an assessment of the inputs used in determining the reported fair values. ASC 820, Fair Value Measurements and Disclosures (“ASC 820”), establishes a hierarchy of inputs used in measuring fair value that maximizes the use of observable inputs and minimizes the use of unobservable inputs by requiring that the observable inputs be used when available.

Observable inputs are inputs that market participants would use in pricing the asset or liability based on market data obtained from sources independent of the Company. Unobservable inputs are inputs that reflect the Company’s assumptions about the inputs that market participants would use in pricing the asset or liability, and are developed based on the best information available in the circumstances. The fair value hierarchy applies only to the valuation inputs used in determining the reported fair value of the investments and is not a measure of the investment credit quality. The hierarchy defines three levels of valuation inputs:

Level 1 — Quoted unadjusted prices for identical instruments in active markets.

Level 2 — Quoted prices for similar instruments in active markets, quoted prices for identical or similar instruments in markets that are not active, and model‑derived valuations in which all observable inputs and significant value drivers are observable in active markets.

Level 3 — Model derived valuations in which one or more significant inputs or significant value drivers are unobservable, including assumptions developed by the Company.

The fair value hierarchy prioritizes valuation inputs based on the observable nature of those inputs. Assets and liabilities measured at fair value are classified in their entirety based on the lowest level of input that is significant to the fair value measurement. The Company’s assessment of the significance of a particular input to the fair value measurement in its entirety requires management to make judgments and consider factors specific to the asset or liability (Note 3).

For certain financial instruments, including accounts receivable, prepaid expenses and other current assets, accounts payable and accrued expenses, the carrying amounts approximate their fair values as of December 31, 2017 and 2016 because of their short-term nature. At December 31, 2017 and 2016, the carrying value of the Company’s debt approximated fair value, which was determined using Level 3 inputs, using market quotes from brokers and is based on current rates offered for similar debt (Note 6).

Property and Equipment

Property and equipment are recorded at cost and depreciated over their estimated useful lives using the straight‑line method. Property and equipment includes raw materials, work-in-process and finished instruments that are Company-owned or expected to remain Company-owned when placed in service. Company-owned instruments are instruments that are manufactured and placed with customers in connection with reagent rental agreements, or are used for internal purposes. Repairs and maintenance costs are expensed as incurred, whereas major improvements are capitalized as additions to property and equipment.

Revenue Recognition

The Company generates revenue from product sales, which includes the sale of instruments, consumable diagnostic tests and related services, and research and development agreements with third parties. The Company recognizes revenue in accordance with FASB ASC Topic 605, Revenue Recognition (“ASC 605”). Accordingly, the Company recognizes revenue when all of the following criteria have been met:

i. Persuasive evidence of an arrangement exists

ii. Delivery has occurred or services have been rendered

iii. The seller’s price to the buyer is fixed or determinable

iv. Collectability is reasonably assured

If any of the above criteria have not been met, the Company defers revenue until such time each of the criteria have been satisfied.

Product revenue is generated by the sale of instruments and consumable diagnostic tests predominantly through its direct sales force in the United States, and distributors in geographic regions outside the United States. The Company does not offer product return or exchange rights (other than those relating to defective goods under warranty) or price protection allowances to its customers, including its distributors. Payment terms granted to distributors are the same as those granted to end-user customers and payments are not dependent upon the distributors’ receipt of payment from their end-user customers. The Company either sells instruments to customers and international distributors, or retains title and places the instrument at the customer site pursuant to a reagent rental agreement. When the instrument is directly purchased by a customer, the Company recognizes revenue when all applicable revenue recognition criteria are met. When the instrument is placed under a reagent rental agreement, the Company’s customers generally agree to fixed term agreements, which can be extended, certain of which may include minimum purchase commitments and/or incremental charges on each consumable diagnostic test purchased, which varies based on the volume of test cartridges purchased. Revenue from the sale of consumable diagnostic tests, which includes the incremental charge, is recognized upon delivery as a component of product revenue in the Company’s consolidated statements of operations and comprehensive loss.

Direct sales of instruments to U.S. customers include warranty, maintenance and technical support services for one year following the installation of the purchased instrument (“Maintenance Services”). After the completion of the initial Maintenance Services period, customers have the option to renew the Maintenance Services for additional one year periods in exchange for additional consideration. In addition, the Company may provide training to customers. The Company defers revenue from the initial sale of the instrument equal to the contract value of the one year of Maintenance Services and recognizes the amounts ratably over the service delivery period.

The Company warrants that consumable diagnostic tests will be free from defects, when handled according to product specifications, for the stated life of the product. To fulfill valid warranty claims, the Company provides replacement product free of charge. Accordingly, the Company accrues warranty expense associated with the estimated defect rates of the consumable diagnostic tests.

The Company does not offer rights of return for instruments or consumable diagnostic tests.

Shipping and handling costs incurred associated with products sold to customers are recorded as a cost of product revenue in the consolidated statement of operations and comprehensive loss. Shipping and handling costs billed to customers in connection with a product sale are recorded as a component of product revenue in the consolidated statements of operations and comprehensive loss.

For multiple-element arrangements, the Company identifies the deliverables included within each agreement and evaluates which deliverables represent separate units of accounting. The determination that multiple elements in an arrangement meet the criteria for separate units of accounting requires the Company’s management to exercise judgment. The Company accounts for those components as separate elements when the following criteria are met: (1) the delivered items have value to the customer on a stand-alone basis; and, (2) if there is a general right of return relative to the delivered items, delivery or performance of the undelivered items is considered probable and within its control.

The consideration received is allocated among the separate units of accounting based on a selling price hierarchy. The selling price hierarchy is based on: (1) vendor specific objective evidence (“VSOE”), if available; (2) third party evidence of selling price if VSOE is not available; or (3) best estimated selling price (“BESP”) if neither VSOE nor third party evidence is available. The Company generally expects that it will not be able to establish selling price using third-party evidence due to the nature of our products and the markets in which the Company competes, and, as such, the Company typically will determine selling price using VSOE or BESP.

When the Company establishes selling price using BESP, consideration is given to both market and Company-specific factors, including the cost to produce the deliverable and the anticipated margin on that deliverable, as well as the characteristics of markets in which the deliverable is sold.

Revenue earned from activities performed pursuant to research and development agreements is reported as research revenue in the consolidated statements of operations and comprehensive loss, using the proportional performance method as the work is completed, limited to payments earned, and the related costs are expensed as incurred as research and development expense. The timing of receipt of cash from the Company’s research and development agreements generally differs from when revenue is recognized.

Product Recall

In July 2016, the Company initiated a voluntary recall and replacement of its T2Candida cartridges at certain customer sites because T2Candida was experiencing higher than normal invalid test rates as the T2Candida cartridges aged. As of June 30, 2016, as a result of this voluntary recall, the Company deferred revenue totaling $149,000 and recorded additional costs of product revenue of $41,000 related to returned products, which are no longer usable. As of December 31, 2017 there were no balances remaining related to this voluntary recall. As of December 31, 2016, the Company had approximately $37,000 of deferred revenue and $3,000 of warranty reserve remaining, both related to this voluntary recall. The impact of the voluntary recall on T2Candida cartridges in inventory was not material to the consolidated financial statements.

Cost of Product Revenue

Cost of product revenue includes the cost of materials, direct labor and manufacturing overhead costs used in the manufacture of consumable diagnostic tests sold to customers and related license and royalty fees. Cost of product revenue also includes depreciation on revenue generating T2Dx that have been placed with customers under reagent rental agreements; costs of materials, direct labor and manufacturing overhead costs on the T2Dx sold to customers; and other costs such as customer support costs, royalties and license fees, warranty and repair and maintenance expense on the T2Dx that have been placed with customers under reagent rental agreements.

Research and Development Costs

Costs incurred in the research and development of the Company’s product candidates are expensed as incurred. Research and development expenses consist of costs incurred in performing research and development activities, including activities associated with performing services under research revenue arrangements, costs associated with the manufacture of developed products and include salaries and benefits, stock compensation, research‑related facility and overhead costs, laboratory supplies, equipment and contract services.

Impairment of Long Lived Assets

The Company reviews long‑lived assets, including capitalized T2 owned instruments and components, for impairment whenever events or changes in circumstances indicate that the carrying amount of an asset may not be recoverable. If indications of impairment exist, projected future undiscounted cash flows associated with the asset or asset group are compared to the carrying amount to determine whether the asset’s value is recoverable. During this review, the Company reevaluates the significant assumptions used in determining the original cost and estimated lives of long‑lived assets. Although the assumptions may vary from asset to asset, they generally include operating results, changes in the use of the asset, cash flows and other indicators of value. Management then determines whether the remaining useful life continues to be appropriate or whether there has been an impairment of long‑lived assets based primarily upon whether expected future undiscounted cash flows are sufficient to support the assets’ recovery. If impairment exists, the Company would adjust the carrying value of the asset to fair value, generally determined by a discounted cash flow analysis. If the carrying value of the asset exceeds such projected undiscounted cash flows, the asset will be written down to its estimated fair value.

Comprehensive Loss

Comprehensive loss is defined as the change in equity of a business enterprise during a period from transactions and other events and circumstances from non‑owner sources. Comprehensive loss consists of net loss and other comprehensive loss, which includes certain changes in equity that are excluded from net loss. The Company’s comprehensive loss equals reported net loss for all periods presented.

Stock-Based Compensation

The Company has a stock‑based compensation plan which is more fully described in Note 8. The Company records stock‑based compensation for options granted to employees and to members of the board of directors for their services on the board of directors, based on the grant date fair value of awards issued, and the expense is recorded on a straight‑line basis over the applicable service period, which is generally four years. The Company accounts for non‑employee stock‑based compensation arrangements based upon the fair value of the consideration received or the equity instruments issued, whichever is more reliably measurable. The measurement date for non‑employee awards is generally the date that the performance of services required for the non‑employee award is complete. Stock‑based compensation costs for non‑employee awards is recognized as services are provided, which is generally the vesting period, on a straight‑line basis.

The Company records the expense for stock option grants that vest upon achievement of performance-based milestones using the accelerated attribution method over the remaining service period when management determines that achievement of the milestone is probable. Management evaluates when the achievement of a performance-based milestone is probable based on the relative satisfaction of the performance conditions as of the reporting date.

The Company expenses restricted stock awards based on the fair value of the award on the date of issuance, on a straight‑line basis over the associated service period of the award.

The Company uses the Black‑Scholes‑Merton option pricing model to determine the fair value of stock options. The use of the Black‑Scholes‑Merton option‑pricing model requires management to make assumptions with respect to the expected term of the option, the expected volatility of the common stock consistent with the expected life of the option, risk‑free interest rates and expected dividend yields of the common stock. The expected term was determined according to the simplified method, which is the average of the vesting tranche dates and the contractual term. Due to the lack of company specific historical and implied volatility data resulting from our limited public market trading history, we have based our estimate of expected volatility primarily on the historical volatility of a group of similar companies that are publicly traded. For these analyses, companies with comparable characteristics are selected, including enterprise value and position within the industry, and with historical share price information sufficient to meet the expected life of the stock‑based awards. The Company computes the historical volatility data using the daily closing prices for the selected companies’ shares during the equivalent period of the calculated expected term of its stock‑based awards. The risk‑free interest rate is determined by reference to U.S. Treasury zero‑coupon issues with remaining maturities similar to the expected term of the options. The Company has not paid, and does not anticipate paying, cash dividends on shares of common stock; therefore, the expected dividend yield is assumed to be zero. The Company has elected an accounting policy to estimate forfeitures at the time of grant and revise those estimates in subsequent periods if actual forfeitures differ from those estimates.

Income Taxes

The Company provides for income taxes using the liability method. The Company provides deferred tax assets and liabilities for the expected future tax consequences of temporary differences between the Company’s financial statement carrying amounts and the tax basis of assets and liabilities using enacted tax rates expected to be in effect in the years in which the differences are expected to reverse. A valuation allowance is provided to reduce the deferred tax assets to the amount that will more likely than not be realized.

The Company applies ASC 740 Income Taxes (“ASC 740”) in accounting for uncertainty in income taxes. The Company does not have any material uncertain tax positions for which reserves would be required. The Company will recognize interest and penalties related to uncertain tax positions, if any, in income tax expense.

The Tax Cuts and Jobs Act (“the Act”) was enacted on December 22, 2017. The Act reduces the US federal corporate tax rate from 35% to 21%, requires companies to pay a one-time transition tax on earnings of certain foreign subsidiaries that were previously tax deferred and creates new taxes on certain foreign sourced earnings. On December 22, 2017, the Securities and Exchange Commission issued guidance under Staff Accounting Bulletin No. 118, Income Tax Accounting Implications of the Tax Cuts and Jobs Act (“SAB 118”) directing taxpayers to consider the impact of the U.S. legislation as “provisional” when it does not have the necessary information available, prepared or analyzed (including computations) in reasonable detail to complete its accounting for the change in tax law.

Guarantees

As permitted under Delaware law, the Company indemnifies its officers and directors for certain events or occurrences while the officer or director is, or was, serving at the Company’s request in such capacity. The term of the indemnification is for the officer’s or director’s lifetime. The maximum potential amount of future payments the Company could be required to make is unlimited; however, the Company has directors’ and officers’ insurance coverage that limits its exposure and enables it to recover a portion of any future amounts paid.

The Company leases office, laboratory and manufacturing space under noncancelable operating leases. The Company has standard indemnification arrangements under the leases that require it to indemnify the landlord against all costs, expenses, fines, suits, claims, demands, liabilities, and actions directly resulting from any breach, violation or nonperformance of any covenant or condition of the Company’s leases.

In the ordinary course of business, the Company enters into indemnification agreements with certain suppliers and business partners where the Company has certain indemnification obligations limited to the costs, expenses, fines, suits, claims, demands, liabilities and actions directly resulting from the Company’s gross negligence or willful misconduct, and in certain instances, breaches, violations or nonperformance of covenants or conditions under the agreements.

As of December 31, 2017 and 2016, the Company had not experienced any material losses related to these indemnification obligations, and no material claims with respect thereto were outstanding. The Company does not expect significant claims related to these indemnification obligations and, consequently, concluded that the fair value of these obligations is negligible, and no related reserves were established.

Net Loss Per Share

Basic net loss per share is calculated by dividing net loss applicable to common stockholders by the weighted‑average number of shares outstanding during the period, without consideration for common stock equivalents. Diluted net loss per share is calculated by adjusting the weighted‑average number of shares outstanding for the dilutive effect of common stock equivalents outstanding for the period, determined using the treasury‑stock method. For purposes of the diluted net loss per share calculation warrants to purchase common stock, stock options and unvested restricted stock are considered to be common stock equivalents, but have been excluded from the calculation of diluted net loss per share, as their effect would be anti‑dilutive for all periods presented. Therefore, basic and diluted net loss per share applicable to common stockholders were the same for all periods presented.

Recent Accounting Standards

From time to time, new accounting pronouncements are issued by the FASB or other standard setting bodies and adopted by the Company as of the specified effective date. Unless otherwise discussed, the Company believes that the impact of recently issued standards that are not yet effective will not have a material impact on its financial position or results of operations upon adoption.

Accounting Standards Adopted

In July 2015, the FASB issued ASU No. 2015-11, Inventory (Topic 330): Simplifying the Measurement of Inventory (“ASU 2015-11”). The standard simplifies the subsequent measurement of inventory by requiring inventory to be measured at the lower of cost and net realizable value for entities using the first-in-first out method of valuing inventory. ASU 2015-11 eliminates other measures required by current guidance to determine net realizable value. ASU 2015-11 is effective for fiscal years beginning after December 15, 2016 and interim periods within those fiscal years and early adoption is permitted. The Company’s adoption of this standard did not have a material effect on its consolidated financial statements.

In March 2016, the FASB released ASU No. 2016-09 Improvements to Employee Share-Based Payment Accounting (“ASU 2016-09”) which is intended to simplify income tax accounting for excess tax benefits, accounting for forfeitures, and employer statutory withholding. Under the current guidance, excess tax benefits that result from an award vesting or settling are recognized in additional paid-in capital in the period that they reduce cash taxes payable. This requires the provision to be computed on a with and without option basis and may result in net operating loss and credit carryforwards on the balance sheet being less than what is available on the tax return. Under the new guidance, the income tax effects of awards will be recognized as a component of income tax expense when the awards vest or are settled (regardless if cash taxes are reduced). For interim reporting purposes, companies will account for excess tax benefits and tax deficiencies as discrete items in the period during which they occurred. The guidance is effective for public entities for fiscal years beginning after December 15, 2016, and interim periods within those years. Early adoption is permitted, however all of the guidance included in the update must be applied when adopted. The Company must use a modified retrospective transition method for adopting and record the cumulative effect of all unrecognized benefits and any change in valuation allowances at the end of the prior tax period as an adjustment to retained earnings. The Company’s adoption of this standard did not have a material effect on its consolidated financial statements and prior periods have not been adjusted. As a result, the Company established a net operating loss deferred tax asset of $1.2 million to account for prior period excess tax benefits through retained earnings, however an offsetting valuation allowance of $1.2 million will also be established through retained earnings because it is not more likely than not that the deferred tax asset will be realized due to historical and expected future losses, such that there is no impact on the Company’s consolidated financial statements. The Company also elected to maintain the use of estimated forfeitures in the calculation of stock based compensation.

In March 2016, the FASB issued ASU No. 2016-06, Derivatives and Hedging (Topic 815): Contingent Put and Call Options in Debt Instruments (“ASU 2016-06”), which applies to all issuers of or investors in debt instruments with embedded call or put options. ASU 2016-06 clarifies the requirements for assessing whether contingent call or put options that can accelerate the payment of principal on debt instruments are clearly and closely related to their debt hosts. Entities performing the assessment under the guidance of ASU 2016-06 are required to assess the embedded call or put options solely in accordance with the four-step decision process. In addition, ASU 2016-06 clarifies what steps are required when assessing whether the economic characteristics and risks of call or put options are clearly and closely related to the economic characteristics and risks of their debt hosts. ASU 2016-06 is effective for financial statements issued for fiscal years beginning after December 15, 2016 and interim periods within those fiscal years using the modified retrospective method for existing debt instruments. The Company’s adoption of this standard did not have a material effect on its consolidated financial statements.

Accounting Standards Issued, Not Adopted

In August 2016, the FASB issued ASU 2016-15, Statement of Cash Flows (Topic 230): Classification of Certain Cash Receipts and Cash Payments (“ASC 2016-15”), which provides guidance on the classification of certain specific cash flow issues including debt prepayment or extinguishment costs, settlement of certain debt instruments, contingent consideration payments made after a business combination, proceeds from the settlement of certain insurance claims and distributions received from equity method investees. The standard requires the use of a retrospective approach to all periods presented, but may be applied prospectively if retrospective application would be impracticable. The guidance is effective for public entities for fiscal years beginning after December 15, 2017, and interim periods within those years, and early application is permitted. The Company is currently evaluating the impact of its pending adoption of ASU 2016-15 on the Company’s consolidated financial statements.

In February 2016, the FASB issued ASU No. 2016-02, Leases (“ASU 2016-02”), which applies to all leases. Under ASU 2016-02, a right-of-use asset and lease obligation will be recorded for all leases, whether operating or financing leases, while the statement of operations will reflect lease expense for operating leases and amortization and interest expense for financing leases. ASU 2016-02 is effective for fiscal years beginning after December 15, 2018 and interim periods within those years, which is the year ended December 31, 2019 for the Company. Entities are required to use a modified retrospective approach of adoption for leases that exist or are entered into after the beginning of the earliest comparative period in the financial statements. Full retrospective application is prohibited. The Company is evaluating the new guidance and the expected effect on the Company’s consolidated financial statements.

In June 2014, the FASB issued amended guidance, ASU No. 2014-09, Revenue from Contracts with Customers (“ASU 2014-09”), which is applicable to revenue recognition that will be effective for the Company for the year ending December 31, 2018, as a result of the deferral of the effective date adopted by the FASB in July 2015. The new guidance must be adopted using either a full retrospective approach for all periods presented or a modified retrospective approach. Early adoption prior to the original adoption date (annual reporting periods beginning after December 15, 2016) of ASU 2014-09 is not permitted. The new guidance applies a more principles-based approach to revenue recognition. The Company will adopt the new standard, effective January 1, 2018, under the modified retrospective method.

The Company established an implementation team to assess the potential impacts of the new standard and prepare for adoption. The implementation team has reviewed current accounting policies and practices and identified potential differences resulting from the application of the new standard. Findings and progress of the project have been regularly communicated to the Audit Committee and senior management.

The qualitative assessment of the standard provided below are estimates of the expected effects of the adoption of ASC 606. This represents our best estimate of the effects of adopting ASC 606 at the time of the preparation of this Annual Report on Form 10-K. The actual impact of ASC 606 is subject to change from these estimates and such change may be significant, pending the completion of our assessment in the first quarter of 2018.

The implementation team is in the process of completing an analysis of our revenue generating arrangements, including direct sales of instruments and consumables, sales of instruments and consumables to distributors, reagent rental agreements and research agreements. A detailed policy for each revenue stream has been drafted. The Company is in the process of implementing appropriate changes to controls, processes, and systems to support recognition and disclosure under the new standard. In addition, the Company continues to monitor changes, modifications, clarifications or interpretations, which may impact the results of adoption, undertaken by the FASB.

The impact of adopting the new standard is not expected to be material to 2017 and 2016 revenue. The most significant impacts of the new standard, upon adoption, are expected to be around the timing of revenue recognition. Specifically, under the new standard:

•

Consideration allocated to the instrument in a direct sale will be recognized upon shipment and consideration allocated to installation will be recognized upon installation. Currently, revenue recognition for both obligations occurs upon installation.

•

Revenue recognition on sales to distributors may be accelerated based on management’s judgement regarding use of the sell-in or sell-through method. Currently, the Company recognizes revenue with new distributors based on the sell-through method, which requires deferral of revenue until product is sold to an end customer.

The Company does not expect the adoption of the new standard to a have material impact on our consolidated balance sheet. The Company does expect significant changes to its financial statement disclosures.

Fair Value Measurements

12 Months Ended

Dec. 31, 2017

Fair Value Disclosures [Abstract]

Fair Value Measurements

3. Fair Value Measurements

The Company measures the following financial assets at fair value on a recurring basis. There were no transfers between levels of the fair value hierarchy during any of the periods presented. The following tables set forth the Company’s financial assets and liabilities carried at fair value categorized using the lowest level of input applicable to each financial instrument as of December 31, 2017 and 2016 (in thousands):

			Quoted Prices
			in Active		Significant
			Markets for		Other		Significant
	Balance at		Identical		Observable		Unobservable
	December 31,		Assets		Inputs		Inputs
	2017		(Level 1)		(Level 2)		(Level 3)
Assets:
Cash	$	3,463	$	3,463	$	—	$	—
Money market funds		38,336		38,336		—		—
Restricted cash		260		260		—		—
	$	42,059	$	42,059	$	—	$	—

Liabilities:
Derivative liability	$	2,238	$	—	$	—	$	2,238
	$	2,238	$	—	$	—	$	2,238

			Quoted Prices
			in Active		Significant
			Markets for		Other		Significant
	Balance at		Identical		Observable		Unobservable
	December 31,		Assets		Inputs		Inputs
	2016		(Level 1)		(Level 2)		(Level 3)
Assets:
Cash	$	16,887	$	16,887	$	—	$	—
Money market funds		56,601		56,601		—		—
Restricted cash		260		260		—		—
	$	73,748	$	73,748	$	—	$	—

The Company’s Term Loan Agreement with CRG (Note 6) contains certain provisions that change the underlying cash flows of the instrument, including an interest-only period dependent on the achievement of the Approval Milestone by April 30, 2018, and acceleration of the obligations under the Loan Agreement under an event of default. In addition, under certain circumstances, a default interest rate of an additional 4.0% per annum will apply at the election of CRG on all outstanding obligations during the occurrence and continuance of an event of default. The Company concluded that these features are not clearly and closely related to the host instrument, and represent a single compound derivative and is required to be re-measured at fair value on a quarterly basis.

During the fourth quarter of 2017, the Company received communication from the FDA that suggested the approval timeline of T2Bacteria could be longer than the Company initially anticipated. The delay resulted in an increase in the probability of not achieving the Approval Milestone by April 30, 2018, as well an increase in the probability of the payment of contingent interest in future periods, based on the contractual payments that exist as of December 31, 2017. As such, in the fourth quarter, the Company recorded a derivative liability related to the Company’s debt agreement with CRG of $2.2 million. The estimated fair value of the derivative liability was determined using a probability-weighted discounted cash flow model that includes principal and interest payments under the following scenarios: FDA approval by April 30, 2017 (40%), FDA approval after April 30, 2017 (20%) and no FDA approval (40%). Should the Company’s assessment of these probabilities change, including amendments of certain revenue targets, there could be a change to the fair value of the derivative liability.

The following table provides a roll-forward of the fair value of the derivative liability (in thousands):

Balance at December 31, 2016

—

Change in fair value of derivative liability, recorded as interest

expense

2,238

Balance at December 31, 2017

2,238

- Definition

The entire disclosure for the fair value of financial instruments (as defined), including financial assets and financial liabilities (collectively, as defined), and the measurements of those instruments as well as disclosures related to the fair value of non-financial assets and liabilities. Such disclosures about the financial instruments, assets, and liabilities would include: (1) the fair value of the required items together with their carrying amounts (as appropriate); (2) for items for which it is not practicable to estimate fair value, disclosure would include: (a) information pertinent to estimating fair value (including, carrying amount, effective interest rate, and maturity, and (b) the reasons why it is not practicable to estimate fair value; (3) significant concentrations of credit risk including: (a) information about the activity, region, or economic characteristics identifying a concentration, (b) the maximum amount of loss the entity is exposed to based on the gross fair value of the related item, (c) policy for requiring collateral or other security and information as to accessing such collateral or security, and (d) the nature and brief description of such collateral or security; (4) quantitative information about market risks and how such risks are managed; (5) for items measured on both a recurring and nonrecurring basis information regarding the inputs used to develop the fair value measurement; and (6) for items presented in the financial statement for which fair value measurement is elected: (a) information necessary to understand the reasons for the election, (b) discussion of the effect of fair value changes on earnings, (c) a description of [similar groups] items for which the election is made and the relation thereof to the balance sheet, the aggregate carrying value of items included in the balance sheet that are not eligible for the election; (7) all other required (as defined) and desired information.

+ References + Details

Supplemental Balance Sheet Information

12 Months Ended

Dec. 31, 2017

Organization Consolidation And Presentation Of Financial Statements [Abstract]

Supplemental Balance Sheet Information

5. Supplemental Balance Sheet Information

Property and Equipment

Property and equipment consists of the following (in thousands)

	Estimated Useful	December 31,			December 31,
	Life (Years)	2017			2016
Office and computer equipment	3	$	409		$	409
Software	3		743			708
Laboratory equipment	5		4,224			4,516
Furniture	5-7		200			200
Manufacturing equipment	5		910			897
Manufacturing tooling and molds	0.5		255			154
T2-owned instruments and components	5		7,370			9,119
Leasehold improvements	Lesser of useful life or lease term		3,437			3,353
Construction in progress	n/a		1,591			1,299
			19,139			20,655
Less accumulated depreciation and amortization			(9,124	)		(7,066	)
Property and equipment, net		$	10,015		$	13,589

Construction in progress is primarily comprised of equipment and leasehold improvement construction projects that have not been placed in service. T2-owned instruments and components is comprised of raw materials and work-in-process inventory that are expected to be used or used to produce Company-owned instruments, based on our business model and forecast, and completed instruments that will be used for internal research and development or reagent rental agreements with customers. Completed T2-owned instruments are placed in service once installation procedures are completed and are depreciated over five years. Depreciation expense for T2-owned instruments placed at customer sites pursuant to reagent rental agreements is recorded as a component of cost of product revenue and totaled $1.0 million and $0.6 million for the years ended December 31, 2017 and December 31, 2016, respectively. Depreciation expense for T2-owned instruments used for internal research and development is recorded as a component of research and development expense.

Depreciation and amortization expense of $2.9 million, $2.3 million and $1.5 million was charged to operations for the years ended December 31, 2017, 2016 and 2015, respectively.

During the fourth quarter of 2017, the Company received communication from the FDA that suggested the approval timeline would be longer than the company initially anticipated. The Company assessed the recoverability of T2-owned instruments based on delayed T2Bacteria cash flows and recorded an impairment charge of $2.6 million, related to T2-owned instruments and components, which is recorded in the cost of product revenue in the Consolidated Statements of Operations and Comprehensive Loss. The fair value used in the impairment calculation was based on the best estimated selling price of the underlying T2-owned instruments, less the estimated cost to sell the instruments.

Accrued Expenses

Accrued expenses consist of the following (in thousands):

	December 31,		December 31,
	2017		2016
Accrued payroll and compensation	$	2,793	$	2,479
Accrued research and development expenses		818		846
Accrued professional services		1,018		884
Other accrued expenses		1,589		699
Total accrued expenses	$	6,218	$	4,908

The Company classified $0.6 million, related to a fee associated with the Company’s Term Loan Agreement (Note 6), from other liabilities to accrued expenses and other current liabilities, as of December 31, 2017, to match the classification of the associated debt.

Notes Payable

12 Months Ended

Dec. 31, 2017

Debt Disclosure [Abstract]

Notes Payable

6. Notes Payable

Future principal payments on the notes payable as of December 31, 2017 are as follows (in thousands):

Year ended December 31,
2018	$	47,483
2019		1,015
2020		-
2021		-
2022		-
Total before unamortized discount and issuance costs		48,498
Less: paid-in-kind interest		(4,347	)
Less: unamortized discount and issuance costs		(2,448	)
Total notes payable	$	41,703

The Term Loan Agreement with CRG is classified as a current liability on the balance sheet at December 31, 2017, based on the Company’s consideration of the probability of violating a minimum liquidity covenant included in the Term Loan Agreement. The contractual terms of the agreement require payments of $5.8 million, $23.0 million and $17.2 million during the years ended December 31, 2020, 2021 and 2022, respectively.

Term Loan Agreement

In December 2016, the Company entered into a Term Loan Agreement (the “Term Loan Agreement”) with CRG. The Company initially borrowed $40.0 million pursuant to the Term Loan Agreement and may borrow up to an additional $10.0 million at any time through and including July 27, 2018, provided that, among other conditions, the Company receives 510(k) clearance for the marketing of T2BacteriaTM by the U.S. Food and Drug Administration (“FDA”) on or before April 30, 2018 (the “Approval Milestone”). The Term Loan Agreement has a six-year term with three years (through December 30, 2019) of interest-only payments, which period shall be extended to four years (through December 30, 2020) if the Company achieves the Approval Milestone, after which quarterly principal and interest payments will be due through the December 30, 2022 maturity date. Interest on the amounts borrowed under the Term Loan Agreement accrues at an annual fixed rate of (a) prior to the Approval Milestone, 12.50%, 4.0% of which may be deferred during the interest-only period by adding such amount to the aggregate principal loan amount and (b) following the Approval Milestone, 11.50%, 3.5% of which may be deferred during the interest-only period by adding such amount to the aggregate principal loan amount. In addition, if the Company achieves certain financial performance metrics, the loan will convert to interest-only until the December 30, 2022 maturity, at which time all unpaid principal and accrued unpaid interest will be due and payable. The Company is required to pay CRG a financing fee based on the loan principal amount drawn. The Company is also required to pay a final payment fee of 8% of the principal outstanding upon repayment. In March 2018 the Term Loan Agreement was amended to extend the Approval Milestone to June 30, 2018, the additional $10.0 million funding through September 27, 2018 and reduce the fiscal year 2018 revenue target to $7.0 million.

The Company may prepay all or a portion of the outstanding principal and accrued unpaid interest under the Term Loan Agreement at any time upon prior notice subject to a certain prepayment fee during the first five years of the term and no prepayment fee thereafter. As security for its obligations under the Term Loan Agreement the Company entered into a security agreement with CRG whereby the Company granted a lien on substantially all of its assets, including intellectual property. The Loan Agreement also contains customary affirmative and negative covenants for a credit facility of this size and type, including a requirement to maintain a minimum cash balance. The Loan Agreement also requires the Company to achieve certain revenue targets, whereby the Company is required to pay double the amount of any shortfall as an acceleration of principal payments. The revenue target for fiscal year 2018 is $7.0 million. The Loan Agreement includes a subjective acceleration clause whereby an event of default, including a material adverse change in the business, operations, or conditions (financial or otherwise), could result in the acceleration of the obligations under the Loan Agreement. Under certain circumstances, a default interest rate of an additional 4.00% per annum will apply at the election of CRG on all outstanding obligations during the occurrence and continuance of an event of default. CRG has not exercised its right under this clause, as there have been no such events. On December 18, 2017, the Term Loan Agreement was amended and the 2017 minimum revenue target was reduced to $3.0 million from $5.0 million.

The Company assessed the terms and features of the Term Loan Agreement, including the interest-only period dependent on the achievement of the Approval Milestone by April 30, 2018, and acceleration of the obligations under the Loan Agreement under an event of default, of the Term Loan Agreement in order to identify any potential embedded features that would require bifurcation. In addition, under certain circumstances, a default interest rate of an additional 4.0% per annum will apply at the election of CRG on all outstanding obligations during the occurrence and continuance of an event of default. The Company concluded that these features are not clearly and closely related to the host instrument, and represent a single compound derivative and is required to be re-measured at fair value on a quarterly basis.

During the fourth quarter of 2017, the Company received communication from the FDA that suggested the approval timeline of T2Bacteria would be longer than the Company initially anticipated. The delay resulted in an increase in the probability of not achieving the Approval Milestone by April 30, 2018, as well an increase in the probability of the payment of contingent interest in future periods, based on the contractual payments requirements that exist as of December 31, 2017. As such, in the fourth quarter, the Company recorded a derivative liability related to the Company’s debt agreement with CRG of $2.2 million (Note 3).

In December 2016, pursuant to the Term Loan Agreement, the Company made an initial draw of $39.2 million, net of financing fees. The Company used approximately $28.0 million of the initial proceeds to repay approximately $27.5 million of outstanding debt pursuant to the Loan and Security Agreement and to repay approximately $0.5 million of outstanding debt pursuant to the Promissory Note. Upon the repayment of all amounts owed by the Company under these agreements, all commitments were terminated and all security interests granted by the Company were released.

In connection with the Term Loan Agreement entered into in December 2016, the Company issued to CRG four separate warrants to purchase a total of 528,958 shares of the Company’s common stock. The warrants are exercisable any time prior to December 30, 2026 at a price of $8.06 per share, with typical provisions for termination upon a change of control or a sale of all or substantially all of the assets of the Company. The warrants are classified within stockholders’ equity, and the proceeds were allocated between the debt and warrants based on their relative fair value. The fair value of the warrants was determined by the Black Scholes Merton option pricing model. The fair value of the warrants at December 30, 2016 was $1.8 million.

Equipment Lease Credit Facility

In October 2015, the Company signed the $10.0 million Credit Facility (the “Credit Facility”) with Essex Capital Corporation (“Essex”) to fund capital equipment needs. As one of the conditions of the Term Loan Agreement, the Credit Facility is capped at a maximum of $5.0 million. Under the Credit Facility, Essex will fund capital equipment purchases presented by the Company. The Company will repay the amounts borrowed in 36 equal monthly installments from the date of the amount funded. At the end of the 36 month lease term, the Company has the option to (a) repurchase the leased equipment at the lesser of fair market value or 10% of the original equipment value, (b) extend the applicable lease for a specified period of time, which will not be less than one year, or (c) return the leased equipment to the Lessor.

In April 2016 and June 2016, the Company completed the first two draws under the Credit Facility of $2.1 million and $2.5 million, respectively. The Company will make monthly payments of $67,000 under the first draw and $79,000 under the second draw. The borrowings under the Credit Facility are treated as capital leases. The amortization of the assets conveyed under the Credit Facility is included as a component of depreciation expense.

Stockholders' Equity	12 Months Ended
Stockholders' Equity	Dec. 31, 2017
Equity [Abstract]
Stockholders' Equity	7. Stockholders’ Equity Common Stock Each share of common stock is entitled to one vote. The holders of common stock are also entitled to receive dividends whenever funds are legally available and when declared by the board of directors, subject to the prior rights of holders of all classes of stock outstanding. As of December 31, 2017, a total of 3,785,083 shares and 1,207,825 shares of common stock were reserved for issuance upon (i) the exercise of outstanding stock options and (ii) the issuance of stock awards under the Company’s 2014 Incentive Award Plan and 2014 Employee Stock Purchase Plan, respectively. Private Investment in Public Equity Financing On September 21, 2016, Canon U.S.A., Inc. (“Canon”) became a related party when the Company sold 6,055,341 shares of its common stock (the “Canon Shares”) to Canon at $6.56 per share, the closing price on this date, for an aggregate cash purchase price of $39.7 million. As of September 21, 2016, the Canon Shares represented 19.9% of the outstanding shares of common stock of the Company. In connection with the director to the Company’s board of directors. On March 20, 2017, the Company filed with the SEC a registration statement on Form S-3 for purposes of registering the resale of the Canon Shares. Confidentially Marketed Public Offering On September 15, 2017, the Company sold 5,031,250 shares of its common stock in a CMPO at $4.00 per share, for an aggregate gross cash purchase price of $20.1 million, or proceeds of $18.8 million after underwriters discount and expenses

Stock-Based Compensation

12 Months Ended

Dec. 31, 2017

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Stock-Based Compensation

8. Stock-Based Compensation

Stock Incentive Plans

2006 Stock Incentive Plan

The Company’s 2006 Stock Option Plan (the “2006 Plan”) was established for granting stock incentive awards to directors, officers, employees and consultants to the Company. Upon closing of the Company’s Initial Public Offering (“IPO”) in August 2014, the Company ceased granting stock incentive awards under the 2006 Plan. The 2006 Plan provided for the grant of incentive and non-qualified stock options and restricted stock grants as determined by the Board of Directors. Under the 2006 Plan, stock options were generally granted with exercise prices equal to or greater than the fair value of the common stock as determined by the board of directors, expired no later than 10 years from the date of grant, and vest over various periods not exceeding 4 years.

2014 Stock Incentive Plan

The Company’s 2014 Plan (the “2014 Plan” and, together with the 2006 Plan, the “Stock Incentive Plans”) provides for the issuance of shares of common stock in the form of stock options, awards of restricted stock, awards of restricted stock unit awards, performance awards, dividend equivalent awards, stock payment awards and stock appreciation rights to directors, officers, employees and consultants of the Company. Since the establishment of the 2014 Plan, the Company has only granted stock options and restricted stock units. Generally, stock options are granted with exercise prices equal to or greater than the fair value of the common stock on the date of grant, expire no later than 10 years from the date of grant, and vest over various periods not exceeding 4 years.

The number of shares reserved for future issuance under the 2014 Plan is the sum of (1) 823,529, (2) any shares that were granted under the 2006 Plan which are forfeited, lapse unexercised or are settled in cash subsequent to the effective date of the 2014 Plan and (3) an annual increase on the first day of each calendar year beginning January 1, 2015 and ending on January 1, 2024, equal to the lesser of (A) 4% of the shares outstanding on the final day of the immediately preceding calendar year and (B) such smaller number of shares determined by the Board of Directors. As of December 31, 2017 there were 1,026,422 shares available for future grant under the Plan.

Stock Options

During the years ended December 31, 2017, 2016, and 2015, the Company granted options with an aggregate fair value of $2.7 million and $7.0 million, and $10.1 million, respectively, which are being amortized into compensation expense over the vesting period of the options as the services are being provided.

The following is a summary of option activity under the Plan (in thousands, except share and per share amounts):

						Weighted-Average
				Weighted-Average		Remaining
	Number of			Exercise Price Per		Contractual Term		Aggregate Intrinsic
	Shares			Share		(In years)		Value
Outstanding at December 31, 2016		4,042,627		$	8.20		7.05	$	4,091
Granted		903,200			5.07
Exercised		(223,352	)		2.36				553
Forfeited		(587,040	)		9.12
Canceled		(350,352	)		11.96
Outstanding at December 31, 2017		3,785,083			7.31		6.88		1,989
Exercisable at December 31, 2017		2,327,392			7.19		5.75		1,923
Vested or expected to vest at December 31, 2017		3,598,126			7.35		6.77		1,977

Included in the stock options outstanding at December 31, 2016 are 146,066 options to purchase common stock granted to certain executive officers of the Company that vest upon the achievement of certain performance conditions, which include the attainment of specified operating result and regulatory targets, by December 31, 2017. Included in the stock options forfeited during the year ended December 31, 2017 are 40,000 options to purchase common stock upon the achievement of certain performance conditions. There are 106,066 performance based options included in the outstanding balance at December 31, 2017. The operating results and regulatory target were not achieved by December 31, 2017, so no expense was recorded.

The weighted‑average fair values of options granted in the years ended December 31, 2017, 2016, and 2015 were $2.95, $4.68, and $8.42 per share, respectively, and were calculated using the following estimated assumptions:

	Year ended
	December 31,
	2017			2016			2015
Weighted-average risk-free interest rate		1.99	%		1.42	%		1.69	%
Expected dividend yield		0.00	%		0.00	%		0.00	%
Expected volatility		60	%		61	%		56	%
Expected terms	6.0 years			6.0 years			6.0 years

The total fair values of stock options that vested during the years ended December 31, 2017, 2016, and 2015 were $3.5 million, $4.9 million, and $4.0 million, respectively.

As of December 31, 2017, there was $5.3 million of total unrecognized compensation cost related to non‑vested stock options granted under the Stock Incentive Plans. Total unrecognized compensation cost will be adjusted for future changes in the estimated forfeiture rate. The Company expects to recognize that cost over a remaining weighted‑average period of 2.3 years as of December 31, 2017.

Restricted Stock Units

During the year ended December 31, 2017 the Company awarded shares of restricted stock units to certain employees at no cost to them, which cannot be sold, assigned, transferred or pledged during the restriction period. The restricted stock and restricted stock units vest through the passage of time, assuming continued employment. Restricted stock units are not included in issued and outstanding common stock until the shares are vested and released. The fair value of the award at the time of the grant is expensed on a straight line basis. The granted restricted stock units had an aggregate fair value of $2.9 million, which are being amortized into compensation expense over the vesting period of the options as the services are being provided.

The following is a summary of restricted stock unit activity under the Plan (in thousands, except share and per share amounts):

				Weighted-Average
	Number of			Grant Date Fair
	Shares			Value
Nonvested at December 31, 2016		272,195		$	5.83
Granted		552,925			5.17
Exercised		(116,173	)		5.83
Forfeited		(102,450	)		5.79
Canceled		—			—
Nonvested at December 31, 2017		606,497			5.23

During the year ended December 31, 2017, 116,173 restricted stock units vested.

As of December 31, 2017, there was $2.5 million of total unrecognized compensation cost related to non‑vested stock options granted under the Stock Incentive Plans. Total unrecognized compensation cost will be adjusted for future changes in the estimated forfeiture rate. The Company expects to recognize that cost over a remaining weighted‑average period of 1.4 years as of December 31, 2017.

Employee Stock Purchase Plan

The 2014 Employee Stock Purchase Plan (the “2014 ESPP”) period is semi-annual and allows participants to purchase the Company’s common stock at 85% of the lower of (i) the market value per share of common stock on the first day of the offering period or (ii) the market value per share of the common stock on the purchase date. Each participant can purchase up to a maximum of $25,000 per calendar year in fair market value. The first plan period began on August 7, 2014. Stock-based compensation expense from the 2014 ESPP for the years ended December 31, 2017, 2016 and 2015 was approximately $0.2 million, $0.3 million and $0.2 million, respectively.

The fair value of the purchase rights granted under this plan was estimated on the date of grant that uses the following weighted-average assumptions, which were derived in a manner similar to those discussed in Note 2 relative to stock options:

	Year ended
	December 31,
	2017			2016			2015
Weighted-average risk-free interest rate		1.03	%		0.50	%		0.19	%
Expected dividend yield		0.00	%		0.00	%		0.00	%
Expected volatility		68	%		67	%		57	%
Expected terms	0.5 years			0.5 years			0.5 years

The 2014 ESPP provides initially for the granting of up to 220,588 shares of the Company’s common stock to eligible employees. In addition, on the first day of each calendar year beginning January 1, 2015 and ending on January 1, 2024, the number of common shares available under the Plan shall be increased by the number of shares equal to the lesser of (1) 1% of the common shares outstanding on the final day of the immediately preceding calendar year and (2) such smaller number of common shares as determined by the Board of Directors. At December 31, 2017, there were 181,403 shares available under the 2014 ESPP.

Stock‑Based Compensation Expense

The following table summarizes the stock-based compensation expense for stock options granted to employees and non-employees, as well as stock-compensation expense for the 2014 ESPP that was recorded in the Company’s results of operations for the years presented (in thousands):

	Year ended
	December 31,
	2017		2016		2015
Cost of product revenue	$	125	$	123	$	—
Research and development		1,384		1,127		1,213
Selling, general and administrative		3,196		3,480		2,840
Total stock-based compensation expense	$	4,705	$	4,730	$	4,053

For the years ended December 31, 2017 and December 31, 2016, $0.1 million and $0.1 million of stock-based compensation expense was capitalized, respectively, as part of inventory or T2-owned instruments and components.

Net Loss Per Share

12 Months Ended

Dec. 31, 2017

Earnings Per Share [Abstract]

Net Loss Per Share

10. Net Loss Per Share

The following table presents the calculation of basic and diluted net loss per share applicable to common stockholders (in thousands, except share and per share data):

	Year ended
	December 31,
	2017			2016			2015
Numerator:
Net loss	$	(62,428	)	$	(54,804	)	$	(45,290	)
Denominator:
Weighted-average number of common shares outstanding — basic and diluted		32,131,512			26,015,751			20,501,748
Net loss per share applicable to common stockholders — basic and diluted	$	(1.94	)	$	(2.11	)	$	(2.21	)

The following shares were excluded from the calculation of diluted net loss per share applicable to common stockholders, prior to the application of the treasury stock method, because their effect would have been anti‑dilutive for the periods presented:

	Year ended
	December 31,
	2017		2016		2015
Options to purchase common shares		3,785,083		4,042,627		3,484,298
Restricted stock units		606,497		272,195		—
Warrants to purchase common stock		528,958		528,958		—
Total		4,920,538		4,843,780		3,484,298

Income Taxes

12 Months Ended

Dec. 31, 2017

Income Tax Disclosure [Abstract]

Income Taxes

11. Income Taxes

The reconciliation of the U.S. federal statutory rate to the Company’s effective tax rate is as follows:

	Year Ended December 31,
	2017			2016			2015
Tax at statutory rates		35.0	%		35.0	%		35.0	%
State income taxes		6.5			5.2			6.6
Permanent differences		(2.5	)		(1.2	)		(1.3	)
Research and development credits		1.5			1.3			1.5
US tax rate change		(52.7	)		—			—
Change in valuation allowance		12.2			(40.3	)		(41.8	)
Effective tax rate		0.0	%		0.0	%		0.0	%

The significant components of the Company’s deferred tax asset consist of the following at December 31, 2017 and 2016 (in thousands):

	December 31,
	2017			2016
Deferred tax assets:
Net operating loss carryforwards	$	62,670		$	69,411
Tax credits		6,924			5,269
Other temporary differences		2,723			1,636
Start-up expenditures		3,214			5,088
Stock option expenses		2,127			2,779
Total deferred tax assets		77,658			84,183
Deferred tax asset valuation allowance		(77,546	)		(83,924	)
Net deferred tax assets		112			259
Deferred tax liabilities:
Prepaid expenses		(112	)		(259	)
Net deferred taxes	$	—		$	—

The Tax Cuts and Jobs Act was enacted in the United States on December 22, 2017. The Act reduces the US federal corporate tax rate from 35% to 21%, requires companies to pay a one-time transition tax on earnings of certain foreign subsidiaries that were previously tax deferred, and creates new taxes on certain foreign sourced earnings. In December 2017, the SEC issued SAB 118, which directs taxpayers to consider the impact of the U.S. legislation as “provisional” when it does not have the necessary information available, prepared or analyzed (including computations) in reasonable detail to complete its accounting for the change in tax law. As of December 31, 2017, we recognized a provisional amount of $0 for the transition tax.

We re-measured certain deferred tax assets and liabilities based on the rates at which they are anticipated to reverse in the future, which is generally 21%. However, we are still examining certain aspects of the Act and refining our calculations, which could potentially affect the measurement of these balances or potentially give rise to new deferred tax amounts. The provisional amount recorded related to the re-measurement of our deferred tax balance was a tax expense of $32.9 million which was offset by an adjustment to the valuation allowance against our deferred taxes of $32.9 million.

In 2017 and 2016, the Company did not record a benefit for income taxes related to its operating losses incurred. ASC 740 requires a valuation allowance to reduce the deferred tax assets reported if, based on the weight of available evidence, it is more likely than not that some portion or all of the deferred tax assets will not be realized. Based upon the level of historical U.S. losses and future projections over the period in which the net deferred tax assets are deductible, at this time, management believes it is more likely than not that the Company will not realize the benefits of these deductible differences, and as a result the Company continues to maintain a valuation allowance for the full amount of the 2017 deferred tax assets. The valuation allowance decreased $6.4 million, and increased $22.1 million and $18.9 million for the years ended December 31, 2017, 2016 and 2015, respectively. The decrease in the 2017 valuation allowance is primarily attributable to the reduction in the US corporate tax rate enacted in Q4 2017. The increase in 2016 and 2015 is primarily related to each year’s taxable loss.

As of December 31, 2017, the Company had federal and state net operating losses of $229.1 million and $237.9 million, respectively, which are available to offset future taxable income, if any, through 2037. The Company also had federal and state research and development tax credits of $4.4 million and $3.2 million, respectively, which expire at various dates through 2037. Under the provisions of the Internal Revenue Code, the net operating loss and tax credit carryforwards are subject to review and possible adjustment by the Internal Revenue Service and state tax authorities. Net operating loss and tax credit carryforwards may become subject to an annual limitation in the event of certain cumulative changes in the ownership interest of significant stockholders over a three-year period in excess of 50%, as defined under Sections 382 and 383 of the Internal Revenue Code, respectively, as well as similar state provisions. This could limit the amount of tax attributes that can be utilized annually to offset future taxable income or tax liabilities. The amount of the annual limitation is determined based on the value of the Company immediately prior to the ownership change. Subsequent ownership changes may further affect the limitation in future years. The Company has completed several financings since its inception which may have resulted in a change in control as defined by Sections 382 and 383 of the Internal Revenue Code, or could result in a change in control in the future. The Company has not conducted an assessment to determine whether there may have been a Section 382 or 383 ownership change.

The Company has no unrecognized tax benefits. Interest and penalty charges, if any, related to uncertain tax positions would be classified as income tax expenses in the accompanying consolidated statements of operations. At December 31, 2017 and 2016, the Company had no accrued interest or penalties related to uncertain tax positions.

The Company files income tax returns in the U.S. federal tax jurisdiction and various state jurisdictions. Since the Company is in a loss carryforward position, the Company is generally subject to examination by the U.S. federal, state and local income tax authorities for all tax years in which a loss carryforward is available. The Company does not have any international operations as of December 31, 2017. The statute of limitations for assessment by federal and state tax jurisdictions in which the Company has business operations is open for tax years ending December 31, 2014, 2015, and 2016. The tax years under examination vary by jurisdiction.

Commitments and Contingencies

12 Months Ended

Dec. 31, 2017

Commitments And Contingencies Disclosure [Abstract]

Commitments and Contingencies

12. Commitments and Contingencies

Operating Leases

In August 2010, the Company entered into a five-year, non-cancelable operating lease for office and laboratory space at its headquarters in Lexington, MA. The lease commenced on January 1, 2011, with the Company providing a security deposit of $400,000. In accordance with the operating lease agreement, the Company reduced its security deposit to $240,000 in May 2015, which is recorded as restricted cash in the consolidated balance sheets. In July 2014, the Company entered into an amendment to expand the office and laboratory space leased. In May 2015, the Company entered into an amendment to extend the term from December 31, 2015 to December 31, 2017. In March 2017, the Company entered into an amendment to extend the term from December 31, 2017 to December 31, 2021. The rent expense, inclusive of the escalating rent payments, is recognized on a straight-line basis over the lease term.

In May, 2013, the Company entered into a two-year operating lease for additional office, laboratory and manufacturing space in Wilmington, MA. The Company entered into an amendment in September 2015 to extend this lease term through December 31, 2017. In August 2017, the Company entered into an amendment to extend the term from December 31, 2017 to December 31, 2018

In November, 2014 the Company entered into an agreement to rent additional office space in Lexington, MA. The term of the agreement is two years, commencing December 2014. In April 2015, the Company entered into an amendment to extend the term of this agreement. The amendment extends the agreement term from December 31, 2016 to December 31, 2017. In connection with this agreement, the Company paid a security deposit totaling $50,000, which is recorded as a component of prepaid assets in the consolidated balance sheets. In May 2015, the Company entered into an amendment to expand existing manufacturing facilities in Lexington, MA. The lease amendment term is June 1, 2015 to December 31, 2017. In September 2017, the Company entered into an amendment to extend the term from December 31, 2017 to December 31, 2021

In November, 2014, the Company entered into a lease for additional laboratory space in Lexington, MA. The lease term commenced April 1, 2015 and extends for six years. The rent expense, inclusive of the escalating rent payments, is recognized on a straight-line basis over the lease term. As an incentive to enter into the lease, the landlord paid approximately $1.4 million of the $2.2 million space build-out costs. The incentive is recorded as a component of lease incentives on the consolidated balance sheets and is amortized as a reduction in rent expense on a straight-line basis over the term of the lease. In connection with this lease agreement, the Company paid a security deposit of $281,000, which is recorded as a component of other assets in the consolidated balance sheets.

Future minimum non-cancelable lease payments under the Company’s operating leases as of December 31, 2017 are as follows (in thousands):

Year ending December 31,
2018	$	2,173
2019		2,149
2020		2,201
2021		1,926
	$	8,449

Rent expense for the years ended December 31, 2017, 2016, and 2015 was $1.9 million, $1.8 million, and $1.6 million, respectively.

License Agreement

In 2006, the Company entered into a license agreement with a third party, pursuant to which the third party granted the Company an exclusive, worldwide, sublicenseable license under certain patent rights to make, use, import and commercialize products and processes for diagnostic, industrial and research and development purposes. The Company agreed to pay an annual license fee ranging from $5,000 to $25,000 for the royalty‑bearing license to certain patents. For the years ended December 31, 2017, 2016 and 2015, the Company incurred $30,000, $31,000 and $34,000, respectively, for regulatory milestones, license fees and reimbursed patent costs under the agreement. The Company also issued a total of 84,678 shares of common stock pursuant to the agreement in 2006 and 2007, which were recorded at fair value at the date of issuance.The Company is required to pay royalties on net sales of products and processes that are covered by patent rights licensed under the agreement at a percentage ranging in the low single digits, subject to reductions and offsets in certain circumstances, as well as a royalty on net sales of products that the Company sublicenses at a low double‑digit percentage of specified gross revenue. Royalties that became due under this agreement for the years ended December 31, 2017 and 2016 were immaterial.

Co-Development Agreements	12 Months Ended
Co-Development Agreements	Dec. 31, 2017
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Co-Development Agreements	14. Co-Development Agreements Canon US Life Sciences On September 21, 2016, Canon became a related party when the Company sold the Canon Shares for an aggregate cash purchase price of $39.7 million, which represented 19.9% of the outstanding shares of common stock of the Company. On February 3, 2015, the Company entered into a Co-Development Partnership Agreement (the “Co-Development Agreement”) with Canon U.S. Life Sciences, Inc. (“Canon US Life Sciences”) to develop a diagnostic test panel to rapidly detect Lyme disease. Under the terms of the Co-Development Agreement, the Company received an upfront payment of $2.0 million from Canon US Life Sciences and the agreement includes an additional $6.5 million of consideration upon achieving certain development and regulatory milestones for total aggregate payments of up to $8.5 million. In October 2015, the Company achieved a specified technical requirement and received $1.5 million related to the achievement of the milestone. The Company is eligible to receive an additional $5.0 million under the arrangement, in two milestone payments of $2.0 million and $3.0 million, related to the achievement of additional development and regulatory milestones. All payments under the Co-Development Agreement are non-refundable once received. The Company will retain exclusive worldwide commercialization rights of any products developed under the Co-Development Agreement, including sales, marketing and distribution and Canon US Life Sciences will not receive any commercial right and will be entitled to only receive royalty payments on the sales of all products developed under the Co-Development Agreement. Either party may terminate the Co-Development Agreement upon the occurrence of a material breach by the other party (subject to a cure period). The Company evaluated the deliverables under the Co-Development Agreement and determined that the Co-Development Agreement included one unit of accounting, the research and development services, as the joint research and development committee deliverable was deemed to be de minimus . The Company is recognizing revenue for research and development services as a component of research revenue in the consolidated financial statements as the services are delivered using the proportional performance method of accounting, limited to payments earned. Costs incurred to deliver the services under the Co-Development Agreement are recorded as research and development expense in the consolidated financial statements. The Company recorded revenue of $0.3 million, $1.8 million and $1.4 million for the years ended December 31, 2017, 2016, and 2015, respectively, under the Co-Development Agreement, and expects to record revenue over the next two years, provided development and regulatory milestones are achieved. Allergan Sales, LLC On November 1, 2016, the Company entered into a Co-Development, Collaboration and Co-Marketing Agreement (the “Allergan Agreement”) with Allergan Sales, LLC (“Allergan Sales”) to develop (1) a direct detection diagnostic test panel that adds one additional bacteria species to the existing T2Bacteria product candidate (the “T2Bacteria II Panel”), and (2) a direct detection diagnostic test panel for testing drug resistance directly in whole blood (the “T2GNR Panel” and, together with the T2Bacteria II Panel, the “Developed Products”). In addition, both the Company and Allergan Sales will participate in a joint research and development committee and Allergan Sales will receive the right to cooperatively market the T2Candida, T2Bacteria, and the Developed Products under the Allergan Agreement to certain agreed-upon customers. Under the terms of the Allergan Agreement, the Company received an upfront payment of $2.0 million from Allergan Sales and will receive additional milestone payments upon achieving certain developmental milestones for total aggregate payments of up to $4.0 million. All payments under the Allergan Agreement are non-refundable once received. The Company will retain exclusive worldwide commercialization rights of any products developed under the Allergan Agreement, including distribution, subject to Allergan Sales’ right to co-market the Developed Products. Allergan Sales, at its election, may co-market T2Candida, T2Bacteria and the Developed Products worldwide to certain agreed-upon customers and will receive royalty based on its sales for a period of time. The Company evaluated the deliverables under the Allergan Agreement and determined that the Allergan Agreement included two units of accounting, the research and development services for the T2Bacteria II Panel and the research and development services for the T2GNR Panel, as the joint research and development committee and right to cooperatively market deliverables were deemed to be de minimus . The Company is recognizing revenue for research and development services as a component of research revenue in the consolidated financial statements as the services are delivered using the proportional performance method of accounting, limited to payments earned. Costs incurred to deliver the services under the Allergan Agreement are recorded as research and development expense in the consolidated financial statements. The Company recorded revenue of $0.9 million during the year ended December 31, 2017 under the Allergan Agreement and expects to record revenue over the next two years, provided development and regulatory milestones are achieved. The Company did not record revenue during the year ended December 31, 2016 under the Allergan Agreement.

Quarterly Financial Data (unaudited)

12 Months Ended

Dec. 31, 2017

Quarterly Financial Information Disclosure [Abstract]

Quarterly Financial Data (unaudited)

15. Quarterly Financial Data (unaudited)

	Year ended December 31, 2017
	(In thousands, except per share data)
	First Quarter			Second Quarter			Third Quarter			Fourth Quarter
Revenue:
Product revenue	$	631		$	735		$	739		$	1,335
Research revenue		310			221			369			326
Total revenue	$	941		$	956		$	1,108		$	1,661
Costs and expenses:
Cost of product revenue		1,627			1,989			2,106			6,306
Research and development		6,585			7,112			5,880			4,156
Selling, general and administrative		5,874			5,759			5,559			5,565
Total costs and expenses		14,086			14,860			13,545			16,027
Loss from operations	$	(13,145	)	$	(13,904	)	$	(12,437	)	$	(14,366	)
Net loss	$	(14,703	)	$	(15,456	)	$	(14,076	)	$	(18,193	)
Per share data:
Net loss per common share—basic and diluted	$	(0.48	)	$	(0.50	)	$	(0.45	)	$	(0.51	)

	Year ended December 31, 2016
	(In thousands, except per share data)
	First Quarter			Second Quarter			Third Quarter			Fourth Quarter
Revenue:
Product revenue	$	437		$	151		$	580		$	579
Research revenue		659			839			504			331
Total revenue	$	1,096		$	990		$	1,084		$	910
Costs and expenses:
Cost of product revenue		1,026			1,781			1,894			2,171
Research and development		6,589			6,369			5,200			5,851
Selling, general and administrative		6,204			6,143			5,935			5,795
Total costs and expenses		13,819			14,293			13,029			13,817
Loss from operations	$	(12,723	)	$	(13,303	)	$	(11,945	)	$	(12,907	)
Net loss	$	(13,426	)	$	(14,046	)	$	(12,783	)	$	(14,549	)
Per share data:
Net loss per common share—basic and diluted	$	(0.55	)	$	(0.58	)	$	(0.51	)	$	(0.48	)

Summary of Significant Accounting Policies (Policies)

12 Months Ended

Dec. 31, 2017

Accounting Policies [Abstract]

Basis of Presentation and Consolidation

Use of Estimates

Segment Information

Off Balance Sheet Risk and Concentrations of Credit Risk

Off‑Balance Sheet Risk and Concentrations of Credit Risk

Cash Equivalents

Accounts Receivable

Inventories

The components of inventory consist of the following (in thousands):

	December 31,		December 31,
	2017		2016
Raw materials	$	539	$	389
Work-in-process		562		351
Finished goods		243		63
Total inventories, net	$	1,344	$	803

Fair Value Measurements

Level 1 — Quoted unadjusted prices for identical instruments in active markets.

Level 3 — Model derived valuations in which one or more significant inputs or significant value drivers are unobservable, including assumptions developed by the Company.

Property and Equipment

Revenue Recognition

i. Persuasive evidence of an arrangement exists

ii. Delivery has occurred or services have been rendered

iii. The seller’s price to the buyer is fixed or determinable

iv. Collectability is reasonably assured

If any of the above criteria have not been met, the Company defers revenue until such time each of the criteria have been satisfied.

The Company does not offer rights of return for instruments or consumable diagnostic tests.

Product Recall

Cost of Product Revenue

Research and Development Costs

Impairment of Long Lived Assets

Comprehensive Loss

Stock Based Compensation

Stock-Based Compensation

The Company expenses restricted stock awards based on the fair value of the award on the date of issuance, on a straight‑line basis over the associated service period of the award.

Income Taxes

Guarantees

Net Loss Per Share

Recent Accounting Standards

Accounting Standards Adopted

Accounting Standards Issued, Not Adopted

•

Summary of Significant Accounting Policies (Tables)

12 Months Ended

Dec. 31, 2017

Accounting Policies [Abstract]

Schedule of inventory

The components of inventory consist of the following (in thousands):

	December 31,		December 31,
	2017		2016
Raw materials	$	539	$	389
Work-in-process		562		351
Finished goods		243		63
Total inventories, net	$	1,344	$	803

Fair Value Measurements (Tables)

12 Months Ended

Dec. 31, 2017

Fair Value Disclosures [Abstract]

Schedule of Financial Assets and Liabilities at Fair value on a Recurring Basis

			Quoted Prices
			in Active		Significant
			Markets for		Other		Significant
	Balance at		Identical		Observable		Unobservable
	December 31,		Assets		Inputs		Inputs
	2017		(Level 1)		(Level 2)		(Level 3)
Assets:
Cash	$	3,463	$	3,463	$	—	$	—
Money market funds		38,336		38,336		—		—
Restricted cash		260		260		—		—
	$	42,059	$	42,059	$	—	$	—

Liabilities:
Derivative liability	$	2,238	$	—	$	—	$	2,238
	$	2,238	$	—	$	—	$	2,238

			Quoted Prices
			in Active		Significant
			Markets for		Other		Significant
	Balance at		Identical		Observable		Unobservable
	December 31,		Assets		Inputs		Inputs
	2016		(Level 1)		(Level 2)		(Level 3)
Assets:
Cash	$	16,887	$	16,887	$	—	$	—
Money market funds		56,601		56,601		—		—
Restricted cash		260		260		—		—
	$	73,748	$	73,748	$	—	$	—

Roll-Forward of Fair Value of Derivative Liability

The following table provides a roll-forward of the fair value of the derivative liability (in thousands):

Balance at December 31, 2016

—

Change in fair value of derivative liability, recorded as interest

expense

2,238

Balance at December 31, 2017

2,238

Supplemental Balance Sheet Information (Tables)

12 Months Ended

Dec. 31, 2017

Organization Consolidation And Presentation Of Financial Statements [Abstract]

Schedule of Property and Equipment

Property and equipment consists of the following (in thousands)

	Estimated Useful	December 31,			December 31,
	Life (Years)	2017			2016
Office and computer equipment	3	$	409		$	409
Software	3		743			708
Laboratory equipment	5		4,224			4,516
Furniture	5-7		200			200
Manufacturing equipment	5		910			897
Manufacturing tooling and molds	0.5		255			154
T2-owned instruments and components	5		7,370			9,119
Leasehold improvements	Lesser of useful life or lease term		3,437			3,353
Construction in progress	n/a		1,591			1,299
			19,139			20,655
Less accumulated depreciation and amortization			(9,124	)		(7,066	)
Property and equipment, net		$	10,015		$	13,589

Components of Accrued Expenses

Accrued expenses consist of the following (in thousands):

	December 31,		December 31,
	2017		2016
Accrued payroll and compensation	$	2,793	$	2,479
Accrued research and development expenses		818		846
Accrued professional services		1,018		884
Other accrued expenses		1,589		699
Total accrued expenses	$	6,218	$	4,908

Notes Payable (Tables)

12 Months Ended

Dec. 31, 2017

Debt Disclosure [Abstract]

Schedule of Debt

Future principal payments on the notes payable as of December 31, 2017 are as follows (in thousands):

Year ended December 31,
2018	$	47,483
2019		1,015
2020		-
2021		-
2022		-
Total before unamortized discount and issuance costs		48,498
Less: paid-in-kind interest		(4,347	)
Less: unamortized discount and issuance costs		(2,448	)
Total notes payable	$	41,703

Stock-Based Compensation (Tables)

12 Months Ended

Dec. 31, 2017

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Summary of Stock Option Activity

The following is a summary of option activity under the Plan (in thousands, except share and per share amounts):

						Weighted-Average
				Weighted-Average		Remaining
	Number of			Exercise Price Per		Contractual Term		Aggregate Intrinsic
	Shares			Share		(In years)		Value
Outstanding at December 31, 2016		4,042,627		$	8.20		7.05	$	4,091
Granted		903,200			5.07
Exercised		(223,352	)		2.36				553
Forfeited		(587,040	)		9.12
Canceled		(350,352	)		11.96
Outstanding at December 31, 2017		3,785,083			7.31		6.88		1,989
Exercisable at December 31, 2017		2,327,392			7.19		5.75		1,923
Vested or expected to vest at December 31, 2017		3,598,126			7.35		6.77		1,977

Schedule of Estimated Assumptions Used to Calculate Weighted-Average Grant Date Fair Value of Options Granted

	Year ended
	December 31,
	2017			2016			2015
Weighted-average risk-free interest rate		1.99	%		1.42	%		1.69	%
Expected dividend yield		0.00	%		0.00	%		0.00	%
Expected volatility		60	%		61	%		56	%
Expected terms	6.0 years			6.0 years			6.0 years

Schedule of Nonvested Restricted Stock Units Activity

The following is a summary of restricted stock unit activity under the Plan (in thousands, except share and per share amounts):

				Weighted-Average
	Number of			Grant Date Fair
	Shares			Value
Nonvested at December 31, 2016		272,195		$	5.83
Granted		552,925			5.17
Exercised		(116,173	)		5.83
Forfeited		(102,450	)		5.79
Canceled		—			—
Nonvested at December 31, 2017		606,497			5.23

Schedule of Estimated Assumptions Used to Calculate Weighted-Average Fair Value of the Purchase Rights Granted

	Year ended
	December 31,
	2017			2016			2015
Weighted-average risk-free interest rate		1.03	%		0.50	%		0.19	%
Expected dividend yield		0.00	%		0.00	%		0.00	%
Expected volatility		68	%		67	%		57	%
Expected terms	0.5 years			0.5 years			0.5 years

Summary of Stock-Based Compensation Expense for Stock Options Granted that was Recorded in the Company's Results of Operations

	Year ended
	December 31,
	2017		2016		2015
Cost of product revenue	$	125	$	123	$	—
Research and development		1,384		1,127		1,213
Selling, general and administrative		3,196		3,480		2,840
Total stock-based compensation expense	$	4,705	$	4,730	$	4,053

Net Loss Per Share (Tables)

12 Months Ended

Dec. 31, 2017

Earnings Per Share [Abstract]

Schedule of basic and diluted net loss per share applicable to common stockholders

The following table presents the calculation of basic and diluted net loss per share applicable to common stockholders (in thousands, except share and per share data):

	Year ended
	December 31,
	2017			2016			2015
Numerator:
Net loss	$	(62,428	)	$	(54,804	)	$	(45,290	)
Denominator:
Weighted-average number of common shares outstanding — basic and diluted		32,131,512			26,015,751			20,501,748
Net loss per share applicable to common stockholders — basic and diluted	$	(1.94	)	$	(2.11	)	$	(2.21	)

Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share

	Year ended
	December 31,
	2017		2016		2015
Options to purchase common shares		3,785,083		4,042,627		3,484,298
Restricted stock units		606,497		272,195		—
Warrants to purchase common stock		528,958		528,958		—
Total		4,920,538		4,843,780		3,484,298

Income Taxes (Tables)

12 Months Ended

Dec. 31, 2017

Income Tax Disclosure [Abstract]

Schedule of Reconciliation of the U.S. Federal Statutory Rate to the Company’s Effective Tax Rate

The reconciliation of the U.S. federal statutory rate to the Company’s effective tax rate is as follows:

	Year Ended December 31,
	2017			2016			2015
Tax at statutory rates		35.0	%		35.0	%		35.0	%
State income taxes		6.5			5.2			6.6
Permanent differences		(2.5	)		(1.2	)		(1.3	)
Research and development credits		1.5			1.3			1.5
US tax rate change		(52.7	)		—			—
Change in valuation allowance		12.2			(40.3	)		(41.8	)
Effective tax rate		0.0	%		0.0	%		0.0	%

Schedule Of Deferred Tax Assets

The significant components of the Company’s deferred tax asset consist of the following at December 31, 2017 and 2016 (in thousands):

	December 31,
	2017			2016
Deferred tax assets:
Net operating loss carryforwards	$	62,670		$	69,411
Tax credits		6,924			5,269
Other temporary differences		2,723			1,636
Start-up expenditures		3,214			5,088
Stock option expenses		2,127			2,779
Total deferred tax assets		77,658			84,183
Deferred tax asset valuation allowance		(77,546	)		(83,924	)
Net deferred tax assets		112			259
Deferred tax liabilities:
Prepaid expenses		(112	)		(259	)
Net deferred taxes	$	—		$	—

Commitments and Contingencies (Tables)

12 Months Ended

Dec. 31, 2017

Commitments And Contingencies Disclosure [Abstract]

Schedule of future minimum lease payments under the Company’s operating leases

Future minimum non-cancelable lease payments under the Company’s operating leases as of December 31, 2017 are as follows (in thousands):

Year ending December 31,
2018	$	2,173
2019		2,149
2020		2,201
2021		1,926
	$	8,449

Quarterly Financial Data (unaudited) (Tables)

12 Months Ended

Dec. 31, 2017

Quarterly Financial Information Disclosure [Abstract]

Schedule of quarterly financial information

	Year ended December 31, 2017
	(In thousands, except per share data)
	First Quarter			Second Quarter			Third Quarter			Fourth Quarter
Revenue:
Product revenue	$	631		$	735		$	739		$	1,335
Research revenue		310			221			369			326
Total revenue	$	941		$	956		$	1,108		$	1,661
Costs and expenses:
Cost of product revenue		1,627			1,989			2,106			6,306
Research and development		6,585			7,112			5,880			4,156
Selling, general and administrative		5,874			5,759			5,559			5,565
Total costs and expenses		14,086			14,860			13,545			16,027
Loss from operations	$	(13,145	)	$	(13,904	)	$	(12,437	)	$	(14,366	)
Net loss	$	(14,703	)	$	(15,456	)	$	(14,076	)	$	(18,193	)
Per share data:
Net loss per common share—basic and diluted	$	(0.48	)	$	(0.50	)	$	(0.45	)	$	(0.51	)

	Year ended December 31, 2016
	(In thousands, except per share data)
	First Quarter			Second Quarter			Third Quarter			Fourth Quarter
Revenue:
Product revenue	$	437		$	151		$	580		$	579
Research revenue		659			839			504			331
Total revenue	$	1,096		$	990		$	1,084		$	910
Costs and expenses:
Cost of product revenue		1,026			1,781			1,894			2,171
Research and development		6,589			6,369			5,200			5,851
Selling, general and administrative		6,204			6,143			5,935			5,795
Total costs and expenses		13,819			14,293			13,029			13,817
Loss from operations	$	(12,723	)	$	(13,303	)	$	(11,945	)	$	(12,907	)
Net loss	$	(13,426	)	$	(14,046	)	$	(12,783	)	$	(14,549	)
Per share data:
Net loss per common share—basic and diluted	$	(0.55	)	$	(0.58	)	$	(0.51	)	$	(0.48	)

Nature of Business - Additional Information (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Cash and cash equivalents	$ 41,799	$ 73,488	$ 73,662	$ 73,849
Accumulated deficit	$ (266,117)	$ (203,689)

Summary of Significant Accounting Policies - Additional Information (Detail)	3 Months Ended								6 Months Ended	12 Months Ended
	Dec. 31, 2017 USD ($) Item	Sep. 30, 2017 USD ($)	Jun. 30, 2017 USD ($)	Mar. 31, 2017 USD ($)	Dec. 31, 2016 USD ($) Item	Sep. 30, 2016 USD ($)	Jun. 30, 2016 USD ($)	Mar. 31, 2016 USD ($)	Jun. 30, 2016 USD ($)	Dec. 31, 2017 USD ($) Segment Item	Dec. 31, 2016 USD ($) Item	Dec. 31, 2015 USD ($)
Product Information [Line Items]
Number of operating segments \| Segment										1
Number of financial institutions in which cash was deposited \| Item	1				1					1	1
Deferred revenue	$ 1,736,000				$ 2,445,000					$ 1,736,000	$ 2,445,000
Cost of product revenue	6,306,000	$ 2,106,000	$ 1,989,000	$ 1,627,000	2,171,000	$ 1,894,000	$ 1,781,000	$ 1,026,000		$ 12,028,000	6,872,000	$ 1,740,000
Vesting period										4 years
Expected dividend yield										0.00%
Net operating loss deferred tax asset	62,670,000				69,411,000					$ 62,670,000	69,411,000
Deferred tax assets, valuation allowance	77,546,000				83,924,000					77,546,000	83,924,000
Accounting Standards Update 201609 Excess Tax Benefit Component [Member] \| Accumulated Deficit [Member]
Product Information [Line Items]
Net operating loss deferred tax asset	1,200,000									1,200,000
Deferred tax assets, valuation allowance	1,200,000									$ 1,200,000
T2 Dx [Member]
Product Information [Line Items]
Maintenance Services period (in years)										1 year
Additional period for Maintenance Service option (in years)										1 year
T2 Candida [Member]
Product Information [Line Items]
Deferred revenue	0				37,000		$ 149,000		$ 149,000	$ 0	37,000
Cost of product revenue									$ 41,000	0
Remaining warranty reserve	$ 0				$ 3,000					$ 0	$ 3,000
Customer One [Member]
Product Information [Line Items]
Total revenue (as a percent)										19.00%	45.00%	50.00%
Customer Two [Member]
Product Information [Line Items]
Total revenue (as a percent)										10.00%	10.00%	25.00%

Summary of Significant Accounting Policies - Components of Inventory (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Inventory Net [Abstract]
Raw materials	$ 539	$ 389
Work-in-process	562	351
Finished goods	243	63
Total inventories, net	$ 1,344	$ 803

Fair Value Measurements - Schedule of Financial Assets and Liabilities at Fair value on a Recurring Basis (Detail) - Estimate of Fair Value Measurement [Member] - Recurring [Member] - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Assets:
Restricted cash	$ 260	$ 260
Total assets	42,059	73,748
Liabilities:
Total Liabilities	2,238
Derivative liability	2,238
Cash [Member]
Assets:
Cash	3,463	16,887
Money Market Funds [Member]
Assets:
Cash	38,336	56,601
Level 1 [Member]
Assets:
Restricted cash	260	260
Total assets	42,059	73,748
Level 1 [Member] \| Cash [Member]
Assets:
Cash	3,463	16,887
Level 1 [Member] \| Money Market Funds [Member]
Assets:
Cash	38,336	$ 56,601
Level 3 [Member]
Liabilities:
Total Liabilities	2,238
Derivative liability	$ 2,238

Fair Value Measurements - Additional Information (Detail) - CRG [Member] - Term Loan Agreement [Member] - USD ($) $ in Millions	1 Months Ended	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Additional interest rate, event of default (as a percent)	4.00%	4.00%
Derivative liability		$ 2.2
FDA approval by April 30, 2017 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated fair value of discount rate		40.00%
FDA approval After April 30, 2017 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated fair value of discount rate		20.00%
No FDA approval [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Estimated fair value of discount rate		40.00%

Fair Value Measurements - Roll-Forward of Fair Value of Derivative Liability (Detail) - Probability-Weighted Discounted Cash Flow Model [Member] $ in Thousands	12 Months Ended
	Dec. 31, 2017 USD ($)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Change in fair value of derivative liability, recorded as interest expense	$ 2,238
Balance at December 31, 2017	$ 2,238

Supplemental Balance Sheet Information - Schedule of Property and Equipment (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Property Plant And Equipment [Line Items]
Property and equipment, gross	$ 19,139	$ 20,655
Less accumulated depreciation and amortization	(9,124)	(7,066)
Property and equipment, net	$ 10,015	13,589
Office and Computer Equipment [Member]
Property Plant And Equipment [Line Items]
Estimated Useful Life (Years)	3 years
Property and equipment, gross	$ 409	409
Software [Member]
Property Plant And Equipment [Line Items]
Estimated Useful Life (Years)	3 years
Property and equipment, gross	$ 743	708
Laboratory Equipment [Member]
Property Plant And Equipment [Line Items]
Estimated Useful Life (Years)	5 years
Property and equipment, gross	$ 4,224	4,516
Furniture [Member]
Property Plant And Equipment [Line Items]
Property and equipment, gross	$ 200	200
Furniture [Member] \| Minimum [Member]
Property Plant And Equipment [Line Items]
Estimated Useful Life (Years)	5 years
Furniture [Member] \| Maximum [Member]
Property Plant And Equipment [Line Items]
Estimated Useful Life (Years)	7 years
Manufacturing Equipment [Member]
Property Plant And Equipment [Line Items]
Estimated Useful Life (Years)	5 years
Property and equipment, gross	$ 910	897
Manufacturing Tooling and Molds [Member]
Property Plant And Equipment [Line Items]
Estimated Useful Life (Years)	6 months
Property and equipment, gross	$ 255	154
T2-Owned Instruments and Components [Member]
Property Plant And Equipment [Line Items]
Estimated Useful Life (Years)	5 years
Property and equipment, gross	$ 7,370	9,119
Leasehold Improvements [Member]
Property Plant And Equipment [Line Items]
Property and equipment, gross	3,437	3,353
Construction in Progress [Member]
Property Plant And Equipment [Line Items]
Property and equipment, gross	$ 1,591	$ 1,299

Supplemental Balance Sheet Information - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Supplemental Balance Sheet Information [Line Items]
Depreciation and amortization		$ 2,940	$ 2,280	$ 1,465
Transfer from other liabilities to accrued expenses and other current liabilities related to fee from debt		$ 585
T2 Owned Instruments in Service [Member]
Supplemental Balance Sheet Information [Line Items]
Estimated useful lives (in years)		5 years
Depreciation expense recorded as a component of cost of product revenue		$ 1,000	$ 600
T2-Owned Instruments and Components [Member]
Supplemental Balance Sheet Information [Line Items]
Estimated useful lives (in years)		5 years
Impairment charges	$ 2,600

Supplemental Balance Sheet Information - Components of Accrued Expenses (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Accrued Liabilities Current [Abstract]
Accrued payroll and compensation	$ 2,793	$ 2,479
Accrued research and development expenses	818	846
Accrued professional services	1,018	884
Other accrued expenses	1,589	699
Total accrued expenses	$ 6,218	$ 4,908

Notes Payable - Future principal payments on notes payable (Details) $ in Thousands	Dec. 31, 2017 USD ($)
Long Term Debt By Maturity [Abstract]
2018	$ 47,483
2019	1,015
Total before unamortized discount and issuance costs	48,498
Less: paid-in-kind interest	(4,347)
Less: unamortized discount and issuance costs	(2,448)
Total notes payable	$ 41,703

Notes Payable - Term Loan Agreement - Additional Information (Detail)	1 Months Ended	12 Months Ended
	Dec. 31, 2016 USD ($) Warrant $ / shares shares	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($) $ / shares shares	Dec. 31, 2015 USD ($)	Mar. 16, 2018 USD ($)	Dec. 18, 2017 USD ($)	Dec. 17, 2017 USD ($)	Dec. 30, 2016 USD ($)
Debt Instrument
Proceeds from issuance of note payable, net			$ 43,803,000	$ 10,000,000
Repayments of note payable		$ 1,194,000	$ 32,404,000	$ 309,000
Common Stock [Member]
Debt Instrument
Number of warrants \| Warrant	4
Number of shares issuable for warrants outstanding (in shares) \| shares	528,958		528,958
Exercise price of warrants \| $ / shares	$ 8.06		$ 8.06
Fair market value of warrants	$ 1,800,000		$ 1,800,000					$ 1,800,000
Loan and Security Agreement [Member]
Debt Instrument
Repayments of note payable	27,500,000
Promissory Note [Member]
Debt Instrument
Repayments of note payable	500,000
CRG [Member] \| Term Loan Agreement [Member]
Debt Instrument
Debt instrument, required payment in December 31, 2020		5,800,000
Debt instrument, required payment in December 31, 2021		23,000,000
Debt instrument, required payment in December 31, 2022		$ 17,200,000
Proceeds from issuance of long-term debt	40,000,000
Line of credit, additional borrowing capacity	$ 10,000,000		$ 10,000,000
Debt term (in years)	6 years
Debt instrument, term of interest-only payments (in years)	3 years
Debt instrument, extended term interest only payments (in years)	4 years
Final fee as a percentage of the principal outstanding (as a percent)	8.00%		8.00%
Debt instrument, prepayment fee term (in years)	5 years
Additional interest rate, event of default (as a percent)	4.00%	4.00%
Debt instrument covenant compliance, minimum revenue target						$ 3,000,000	$ 5,000,000
Debt instrument covenant compliance revenue targeted for next fiscal year		$ 7,000,000
Derivative liability		$ 2,200,000
Proceeds from issuance of note payable, net	$ 39,200,000
Portion of proceeds used for debt repayment	$ 28,000,000
CRG [Member] \| Term Loan Agreement [Member] \| Subsequent Event [Member]
Debt Instrument
Line of credit, additional borrowing capacity					$ 10,000,000
CRG [Member] \| Term Loan Agreement [Member] \| Prior to Approval Milestone [Member]
Debt Instrument
Annual fixed rate (as a percent)	12.50%		12.50%
Deferred interest rate (as a percent)	4.00%
CRG [Member] \| Term Loan Agreement [Member] \| Following Approval Milestone [Member]
Debt Instrument
Annual fixed rate (as a percent)	11.50%		11.50%
Deferred interest rate (as a percent)	3.50%

Notes Payable - Equipment Lease Credit Facility - Additional Information (Detail) - Capital Lease Obligations [Member]	1 Months Ended
	Jun. 30, 2016 USD ($) Draw	Apr. 30, 2016 USD ($)	Oct. 31, 2015 USD ($)
Debt Instrument
Initial borrowing capacity			$ 10,000,000
Maximum borrowings available (up to)			$ 5,000,000
Debt term (in months)			36 months
Repurchase price as percentage of original equipment value that the equipment under lease may be repurchased by lessee			10.00%
Minimum lease period to extend lease (in years)			1 year
Amount of draw	$ 2,500,000	$ 2,100,000
Amount of monthly payment	$ 79,000	$ 67,000
Number of draws \| Draw	2

Stockholders' Equity - Additional Information (Detail) $ / shares in Units, $ in Thousands			12 Months Ended
	Sep. 15, 2017 USD ($) $ / shares shares	Sep. 21, 2016 USD ($) $ / shares shares	Dec. 31, 2017 Item shares	Dec. 31, 2016 USD ($)
Class Of Stock [Line Items]
Number of voting rights per share of common stock \| Item			1
Proceeds from private investment in public equity \| $				$ 39,723
Private Placement [Member]
Class Of Stock [Line Items]
Number of shares sold \| shares		6,055,341
Sale price of stock (in dollars per share) \| $ / shares		$ 6.56
Proceeds from private investment in public equity \| $		$ 39,700
Percentage of common shares outstanding (as a percentage)		19.90%
CMPO [Member]
Class Of Stock [Line Items]
Number of shares sold \| shares	5,031,250
Sale price of stock (in dollars per share) \| $ / shares	$ 4.00
Proceeds from private investment in public equity \| $	$ 20,100
Proceeds from private investment in public equity after underwriters discount and expenses \| $	$ 18,800
2014 Incentive Award Plan [Member]
Class Of Stock [Line Items]
Common stock were reserved for issuance \| shares			3,785,083
2014 Employee Stock Purchase Plan [Member]
Class Of Stock [Line Items]
Common stock were reserved for issuance \| shares			1,207,825

Stock-Based Compensation - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Share-Based Compensation
Vesting period	4 years
Stock-based compensation expense	$ 4,705,000	$ 4,730,000	$ 4,053,000
Fair value of vested stock options	3,500,000	4,900,000	4,000,000
Unrecognized compensation cost related to unvested stock options	$ 5,300,000
Weighted-average period	2 years 3 months 18 days
T2-Owned Instruments and Components [Member]
Share-Based Compensation
Stock-based compensation expense	$ 100,000	$ 100,000
Performance-based awards [Member]
Share-Based Compensation
Outstanding, end of the period	106,066
Performance-based awards [Member] \| Executive Officer [Member]
Share-Based Compensation
Outstanding, end of the period		146,066
Forfeited performance stock based options	40,000
Stock-based compensation expense	$ 0
Restricted Stock Units [Member]
Share-Based Compensation
Unrecognized compensation cost related to unvested stock options	$ 2,500,000
Weighted-average period	1 year 4 months 24 days
Restricted stock units, vested	116,173
Employee Stock Purchase Plan [Member]
Share-Based Compensation
Shares available for grant	181,403
Stock-based compensation expense	$ 200,000	$ 300,000	200,000
Percentage of full share price paid in purchase of common stock	85.00%
Maximum amount of annual employee common stock purchases	$ 25,000
Shares available for authorization	220,588
Percentage of common shares outstanding	1.00%
2014 Stock Option Plan [Member] \| Stock Options [Member]
Share-Based Compensation
Shares available for future issuance under stock incentive plan	823,529
Percentage of common shares outstanding	4.00%
Shares available for grant	1,026,422
2006 and 2014 Stock Option Plans [Member] \| Stock Options [Member]
Share-Based Compensation
Aggregate fair value of options granted	$ 2,700,000	$ 7,000,000	$ 10,100,000
2006 and 2014 Stock Option Plans [Member] \| Stock Options [Member]
Share-Based Compensation
Outstanding, end of the period	3,785,083	4,042,627
Forfeited performance stock based options	587,040
Weighted average fair value of options granted	$ 2.95	$ 4.68	$ 8.42
2006 and 2014 Stock Option Plans [Member] \| Restricted Stock Units [Member]
Share-Based Compensation
Aggregate fair value of options granted	$ 2,900,000
Maximum [Member] \| 2006 Stock Option Plan [Member] \| Stock Options [Member]
Share-Based Compensation
Expiration period	10 years
Vesting period	4 years
Maximum [Member] \| 2014 Stock Option Plan [Member] \| Stock Options [Member]
Share-Based Compensation
Expiration period	10 years
Vesting period	4 years

Stock-Based Compensation - Summary of Stock Option Activity (Detail) - 2006 and 2014 Stock Option Plans [Member] - Stock Options [Member] - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Share-Based Compensation
Number of Shares Outstanding, beginning of the period	4,042,627
Number of Shares, Granted	903,200
Number of Shares, Exercised	(223,352)
Number of Shares, Forfeited	(587,040)
Number of Shares, Canceled	(350,352)
Number of Shares Outstanding, end of the period	3,785,083	4,042,627
Number of Shares, Exercisable	2,327,392
Number of Shares, Vested or expected to vest	3,598,126
Weighted-Average Exercise Price Per Share Outstanding, beginning of the period	$ 8.20
Weighted-Average Exercise Price Per Share, Granted	5.07
Weighted-Average Exercise Price Per Share, Exercised	2.36
Weighted-Average Exercise Price Per Share, Forfeited	9.12
Weighted-Average Exercise Price Per Share, Canceled	11.96
Weighted-Average Exercise Price Per Share Outstanding, end of the period	7.31	$ 8.20
Weighted-Average Exercise Price Per Share, Exercisable	7.19
Weighted-Average Exercise Price Per Share, Vested or expected to vest	$ 7.35
Weighted-Average Remaining Contractual Term, Outstanding	6 years 10 months 17 days	7 years 18 days
Weighted-Average Remaining Contractual Term, Exercisable	5 years 9 months
Weighted-Average Remaining Contractual Term, Vested or expected to vest	6 years 9 months 7 days
Aggregate Intrinsic Value, Outstanding, beginning of the period	$ 4,091
Aggregate Intrinsic Value, Exercised	553
Aggregate Intrinsic Value Outstanding, end of the period	1,989	$ 4,091
Aggregate Intrinsic Value, Exercisable	1,923
Aggregate Intrinsic Value, Vested or expected to vest	$ 1,977

Stock-Based Compensation - Schedule of Estimated Assumptions Used to Calculate Weighted-Average Grant Date Fair Value of Options Granted (Detail) - Stock Options [Member] - 2006 and 2014 Stock Option Plans [Member]	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Share-Based Compensation
Weighted-average risk-free interest rate	1.99%	1.42%	1.69%
Expected dividend yield	0.00%	0.00%	0.00%
Expected volatility	60.00%	61.00%	56.00%
Expected terms	6 years	6 years	6 years

Stock-Based Compensation - Schedule of Nonvested Restricted Stock Units Activity (Detail) - Restricted Stock Units [Member]	12 Months Ended
	Dec. 31, 2017 $ / shares shares
Share-Based Compensation
Number of Shares, Nonvested restricted shares at the beginning of the period \| shares	272,195
Number of Shares, Restricted shares granted \| shares	552,925
Number of Shares, Restricted shares exercised \| shares	(116,173)
Number of Shares, Restricted shares forfeited \| shares	(102,450)
Number of Shares, Canceled \| shares	0
Number of Shares, Nonvested restricted shares at the end of the period \| shares	606,497
Weighted-Average Grant Date Fair Value, Nonvested restricted shares at the beginning of the period \| $ / shares	$ 5.83
Weighted-Average Grant Date Fair Value, Granted \| $ / shares	5.17
Weighted-Average Grant Date Fair Value, Exercised \| $ / shares	5.83
Weighted-Average Grant Date Fair Value, Forfeited \| $ / shares	5.79
Weighted-Average Grant Date Fair Value, Canceled \| $ / shares	0
Weighted-Average Grant Date Fair Value, Nonvested restricted shares at the end of the period \| $ / shares	$ 5.23

Stock-Based Compensation - Schedule of Estimated Assumptions Used to Calculate Weighted-Average Fair Value of the Purchase Rights Granted (Detail) - Employee Stock Purchase Plan [Member]	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Share-Based Compensation
Weighted-average risk-free interest rate	1.03%	0.50%	0.19%
Expected dividend yield	0.00%	0.00%	0.00%
Expected volatility	68.00%	67.00%	57.00%
Expected terms	6 months	6 months	6 months

Stock-Based Compensation - Summary of Stock-Based Compensation Expense for Stock Options Granted that was Recorded in the Company's Results of Operations (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Stock-based compensation expense
Stock-based compensation expense	$ 4,705	$ 4,730	$ 4,053
Cost of Product Revenue [Member]
Stock-based compensation expense
Stock-based compensation expense	125	123
Research and Development [Member]
Stock-based compensation expense
Stock-based compensation expense	1,384	1,127	1,213
Selling, General and Administrative [Member]
Stock-based compensation expense
Stock-based compensation expense	$ 3,196	$ 3,480	$ 2,840

Warrants - Additional Information (Detail) - Common Stock [Member] $ / shares in Units, $ in Millions	1 Months Ended
	Dec. 31, 2016 USD ($) Warrant $ / shares shares	Dec. 30, 2016 USD ($)
Class Of Warrant Or Right [Line Items]
Number of warrants \| Warrant	4
Number of shares issuable for warrants outstanding \| shares	528,958
Exercise price of warrants \| $ / shares	$ 8.06
Fair market value of warrants \| $	$ 1.8	$ 1.8

Net Loss Per Share (Calc of Basic and Diluted) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Numerator:
Net loss	$ (18,193)	$ (14,076)	$ (15,456)	$ (14,703)	$ (14,549)	$ (12,783)	$ (14,046)	$ (13,426)	$ (62,428)	$ (54,804)	$ (45,290)
Denominator:
Weighted-average number of common shares outstanding — basic and diluted									32,131,512	26,015,751	20,501,748
Net loss per share — basic and diluted	$ (0.51)	$ (0.45)	$ (0.50)	$ (0.48)	$ (0.48)	$ (0.51)	$ (0.58)	$ (0.55)	$ (1.94)	$ (2.11)	$ (2.21)

Net Loss Per Share - Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share (Detail) - shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from the computation of diluted net loss per share	4,920,538	4,843,780	3,484,298
Options to Purchase Common Shares [Member]
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from the computation of diluted net loss per share	3,785,083	4,042,627	3,484,298
Restricted Stock Units [Member]
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from the computation of diluted net loss per share	606,497	272,195
Warrants to Purchase Common Stock [Member]
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from the computation of diluted net loss per share	528,958	528,958

Income Taxes - Schedule of Reconciliation of the U.S. Federal Statutory Rate to the Company's Effective Tax Rate (Details)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Effective Income Tax Rate Reconciliation, Percent.
Tax at statutory rates	35.00%	35.00%	35.00%
State income taxes	6.50%	5.20%	6.60%
Permanent differences	(2.50%)	(1.20%)	(1.30%)
Research and development credits	1.50%	1.30%	1.50%
US tax rate change	(52.70%)
Change in valuation allowance	12.20%	(40.30%)	(41.80%)
Effective tax rate	0.00%	0.00%	0.00%

Income Taxes - Schedule Of Deferred Tax Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Deferred tax assets:
Net operating loss deferred tax asset	$ 62,670	$ 69,411
Tax credits	6,924	5,269
Other temporary differences	2,723	1,636
Start-up expenditures	3,214	5,088
Stock option expenses	2,127	2,779
Total deferred tax assets	77,658	84,183
Deferred tax asset valuation allowance	(77,546)	(83,924)
Net deferred tax assets	112	259
Deferred tax liabilities:
Prepaid expenses	$ (112)	$ (259)

Income Taxes - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Taxes [Line Items]
Tax Cuts and Jobs Act of 2017, provisional income tax expense for transition tax	$ 0
Tax Cuts and Jobs Act of 2017, provisional tax expense related to re-measurement of deferred tax	32,900,000
Tax Cuts and Jobs Act of 2017, adjustment to deferred taxes valuation allowance	32,900,000
Increase (decrease) in valuation allowance	(6,400,000)	$ 22,100,000	$ 18,900,000
Unrecognized tax benefits	0
Accrued interest or penalties related to uncertain tax positions	0	$ 0
Federal [Member]
Income Taxes [Line Items]
Net operating losses	229,100,000
Federal [Member] \| Research and Development [Member]
Income Taxes [Line Items]
Credit carryforward	4,400,000
State [Member]
Income Taxes [Line Items]
Net operating losses	237,900,000
State [Member] \| Research and Development [Member]
Income Taxes [Line Items]
Credit carryforward	$ 3,200,000

Commitments and Contingencies - Additional Information (Details) - USD ($)	1 Months Ended					12 Months Ended			24 Months Ended
	Sep. 30, 2017	Aug. 31, 2017	Nov. 30, 2014	May 31, 2013	Aug. 31, 2010	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2007	May 31, 2015	Jan. 01, 2011	Dec. 31, 2006
Leases
Rent expenses						$ 1,900,000	$ 1,800,000	$ 1,600,000
Payment of license fees and reimbursed patent costs						$ 30,000	$ 31,000	$ 34,000
Shares issued									84,678
Minimum [Member]
Leases
Annual license fee payable												$ 5,000
Maximum [Member]
Leases
Annual license fee payable												$ 25,000
Operating Lease Entered into August 2010 [Member] \| Office and Laboratory Space [Member]
Leases
Lease expiration date						Dec. 31, 2021
Term of lease					5 years
Security deposit										$ 240,000	$ 400,000
Operating Lease Entered into May 2013 [Member] \| Office, Laboratory and Manufacturing Space [Member]
Leases
Lease expiration date		Dec. 31, 2018
Term of lease				2 years
Operating Lease Entered into November 2014 [Member] \| Office Space [Member] \| License Agreement [Member]
Leases
Lease expiration date	Dec. 31, 2021
Term of lease			2 years
Security deposit			$ 50,000
Operating Lease Entered into November 2014 [Member] \| Laboratory Space [Member]
Leases
Term of lease			6 years
Security deposit			$ 281,000
Space build-out costs paid			1,400,000
Space build-out costs to be paid by landlord			$ 2,200,000

Commitments and Contingencies - Future Minimum Lease Payments (Detail) $ in Thousands	Dec. 31, 2017 USD ($)
Future minimum lease payments
2018	$ 2,173
2019	2,149
2020	2,201
2021	1,926
Total	$ 8,449

Co-Development Agreements - Additional Information (Detail)				1 Months Ended	3 Months Ended								12 Months Ended
	Nov. 01, 2016 USD ($) specie	Sep. 21, 2016 USD ($)	Feb. 03, 2015 USD ($) Item	Oct. 31, 2015 USD ($)	Dec. 31, 2017 USD ($) Item	Sep. 30, 2017 USD ($)	Jun. 30, 2017 USD ($)	Mar. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Sep. 30, 2016 USD ($)	Jun. 30, 2016 USD ($)	Mar. 31, 2016 USD ($)	Dec. 31, 2017 USD ($) Item	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Proceeds from sale of shares in related party														$ 39,723,000
Revenues					$ 1,661,000	$ 1,108,000	$ 956,000	$ 941,000	$ 910,000	$ 1,084,000	$ 990,000	$ 1,096,000	$ 4,666,000	4,080,000	$ 2,813,000
Co Development Partnership Agreement [Member] \| Canon U.S. Life Sciences Inc [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Upfront payment			$ 2,000,000
Additional consideration receivable upon achievement of certain development and regulatory milestones			6,500,000
Aggregate consideration receivable			$ 8,500,000
Proceeds received for achievement of milestone				$ 1,500,000
Additional consideration receivable upon achievement of additional development and regulatory milestones					$ 5,000,000								$ 5,000,000
Number of milestone payments \| Item					2								2
Additional consideration receivable upon achievement of development and regulatory milestones, payment one					$ 2,000,000								$ 2,000,000
Additional consideration receivable upon achievement of development and regulatory milestones, payment two					$ 3,000,000								3,000,000
Number of units \| Item			1
Revenues													300,000	1,800,000	$ 1,400,000
Co Development Partnership Agreement [Member] \| Allergan Sales [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Upfront payment	$ 2,000,000
Aggregate consideration receivable	$ 4,000,000
Revenues													$ 900,000	$ 0
Number of additional bacteria species added to existing product candidate \| specie	1
Private Placement [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Proceeds from sale of shares in related party		$ 39,700,000
Percentage of outstanding shares at date of sale		19.90%

Quarterly Financial Data (unaudited) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Revenue:
Product revenue	$ 1,335	$ 739	$ 735	$ 631	$ 579	$ 580	$ 151	$ 437	$ 3,440	$ 1,747	$ 599
Research revenue	326	369	221	310	331	504	839	659	1,226	2,333	2,214
Total revenue	1,661	1,108	956	941	910	1,084	990	1,096	4,666	4,080	2,813
Costs and expenses:
Cost of product revenue	6,306	2,106	1,989	1,627	2,171	1,894	1,781	1,026	12,028	6,872	1,740
Research and development	4,156	5,880	7,112	6,585	5,851	5,200	6,369	6,589	23,733	24,009	25,362
Selling, general and administrative	5,565	5,559	5,759	5,874	5,795	5,935	6,143	6,204	22,757	24,077	19,094
Total costs and expenses	16,027	13,545	14,860	14,086	13,817	13,029	14,293	13,819	58,518	54,958	46,196
Loss from operations	(14,366)	(12,437)	(13,904)	(13,145)	(12,907)	(11,945)	(13,303)	(12,723)	(53,852)	(50,878)	(43,383)
Net loss	$ (18,193)	$ (14,076)	$ (15,456)	$ (14,703)	$ (14,549)	$ (12,783)	$ (14,046)	$ (13,426)	$ (62,428)	$ (54,804)	$ (45,290)
Per share data:
Net loss per common share - basic and diluted (in dollars per share)	$ (0.51)	$ (0.45)	$ (0.50)	$ (0.48)	$ (0.48)	$ (0.51)	$ (0.58)	$ (0.55)	$ (1.94)	$ (2.11)	$ (2.21)

Restricted Cash	12 Months Ended
Restricted Cash	Dec. 31, 2017
Restricted Cash [Abstract]
Restricted Cash	4. Restricted Cash The Company is required to maintain a security deposit for its operating lease agreement for the duration of the lease agreement and for its credit cards as long as they are in place. At both December 31, 2017 and 2016, the Company had certificates of deposit for $260,000, which represented collateral as security deposits for its operating lease agreement for its facility and its credit card.

Warrants	12 Months Ended
Warrants	Dec. 31, 2017
Warrants And Rights Note Disclosure [Abstract]
Warrants Note Disclosure Text Block	9. Warrants In connection with the Term Loan Agreement entered into in December 2016, the Company issued to CRG four separate warrants to purchase a total of 528,958 shares of the Company’s common stock. The warrants are exercisable any time prior to December 30, 2026 at a price of $8.06 per share, with typical provisions for termination upon a change of control or a sale of all or substantially all of the assets of the Company. The warrants are classified within stockholders’ equity, and the proceeds were allocated between the debt and warrants based on their relative fair value. The fair value of the warrants was determined by the Black‑Scholes‑Merton option pricing model. The fair value of the warrants at date of issuance was $1.8 million.

401(k) Savings Plan	12 Months Ended
401(k) Savings Plan	Dec. 31, 2017
Compensation And Retirement Disclosure [Abstract]
401(k) Savings Plan	13. 401(k) Savings Plan In March, 2008, the Company established a retirement savings plan under Section 401(k) of the Internal Revenue Code (the “401(k) Plan”). The 401(k) Plan covers substantially all employees of the Company who meet minimum age and service requirements, and allows participants to defer a portion of their annual compensation on a pretax basis. Company contributions to the 401(k) Plan may be made at the discretion of the board of directors. Company contributions to the 401(k) Plan were $190,000 and $237,000 for the years ended December 31, 2017 and 2016, respectively. No contributions were made during the year ended December 31, 2015.

Restricted Cash - Additional Information (Detail) - USD ($)	Dec. 31, 2017	Dec. 31, 2016
Certificates of deposit [Member]
Restricted cash
Security deposit	$ 260,000	$ 260,000