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Document and Entity Information - shares	3 Months Ended
Document and Entity Information - shares	Mar. 31, 2015	May 13, 2015
Document And Entity Information [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Mar. 31, 2015
Document Fiscal Year Focus	2015
Document Fiscal Period Focus	Q1
Trading Symbol	HSGX
Entity Registrant Name	Histogenics Corporation
Entity Central Index Key	0001372299
Current Fiscal Year End Date	--12-31
Entity Filer Category	Smaller Reporting Company
Entity Common Stock, Shares Outstanding		13,220,012

Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Mar. 31, 2015	Dec. 31, 2014
Current assets:
Cash and cash equivalents	$ 53,181	$ 58,060
Prepaid expenses and other current assets	829	796
Total current assets	54,010	58,856
Property and equipment, net	5,422	4,878
Intangible asset, net	510	510
Noncurrent deferred tax assets, net	1,034	651
Restricted cash	604	604
Total assets	61,580	65,499
Current liabilities:
Accounts payable	3,293	4,886
Accrued expenses	1,896	1,683
Current portion of deferred rent	224	219
Current portion of deferred lease incentive	514	407
Current portion of equipment loan	538	405
Deferred tax liabilities, net	1,034	651
Total current liabilities	7,499	8,251
Deferred rent, long-term	445	379
Deferred lease incentive, long-term	1,213	1,318
Equipment loan, long-term	1,199	1,345
Total liabilities	10,356	11,293
Commitments and contingencies (Note 5)
Stockholders' equity:
Preferred stock, $0.01 par value; authorized shares - 10,000,000 at December 31, 2014 and March 31, 2015; none issued and outstanding at December 31, 2014 and March 31, 2015
Common stock, $0.01 par value; authorized shares - 100,000,000 at December 31, 2014 and March 31, 2015; 12,755,012 shares issued and outstanding at December 31, 2014 and 13,220,012 shares issued and outstanding at March 31, 2015	132	127
Additional paid-in capital	192,597	187,620
Accumulated deficit	(141,505)	(133,541)
Total stockholders' equity	51,224	54,206
Total liabilities and stockholders' equity	$ 61,580	$ 65,499

Condensed Consolidated Balance Sheets (Parenthetical) - $ / shares	Mar. 31, 2015	Dec. 31, 2014
Statement of Financial Position [Abstract]
Preferred stock par value	$ 0.01	$ 0.01
Preferred stock authorized	10,000,000	10,000,000
Preferred stock issued	0	0
Preferred stock outstanding	0	0
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	100,000,000	100,000,000
Common stock, shares issued	13,220,012	12,755,012
Common stock, shares outstanding	13,220,012	12,755,012

Condensed Consolidated Statements of Operations - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Operating expenses:
Research and development	$ 5,764	$ 3,374
General and administrative	2,109	1,799
Total operating expenses	7,873	5,173
Loss from operations	(7,873)	(5,173)
Other income (expense):
Interest expense, net	(62)
Other income (expense), net	(29)	(2)
Change in fair value of warrant liability, other liability and net sales distribution payment liability		1,738
Total other income (expense), net	(91)	1,736
Net loss	$ (7,964)	$ (3,437)
Loss attributable to common stockholders - basic and diluted	$ (7,964)	$ (3,437)
Loss per common share - basic and diluted:	$ (0.60)	$ (5.90)
Weighted-average shares used to compute earnings per common share - basic and diluted:	13,201,186	582,246

Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
CASH FLOWS FROM OPERATING ACTIVITIES:
Net loss	$ (7,964)	$ (3,437)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation	371	153
Deferred rent and lease incentive	73	(74)
Stock-based compensation	235	76
Non-cash consulting expense	9
Change in fair value of liabilities		(1,738)
Amortization of deferred financing costs		(38)
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	(33)	243
Accounts payable	(1,593)	34
Accrued expenses	213	(238)
Net cash used in operating activities	(8,689)	(5,019)
CASH FLOWS FROM INVESTING ACTIVITIES:
Purchases of property and equipment	(915)	(120)
Net cash used in investing activities	(915)	(120)
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from overallotment, net of issuance costs of $377	4,738
Payment on equipment term loan	(13)
Costs associated with Initial Public Offering		(235)
Net cash provided by (used in) financing activities	4,725	(235)
Net change in cash and cash equivalents	(4,879)	(5,374)
Cash and cash equivalents - Beginning of period	58,060	8,734
Cash and cash equivalents - End of period	$ 53,181	$ 3,360

Condensed Consolidated Statements of Cash Flows (Parenthetical) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Statement of Cash Flows [Abstract]
Issuance costs	$ 377	$ 377

Nature of Business

3 Months Ended

Mar. 31, 2015

Accounting Policies [Abstract]

Nature of Business

1. NATURE OF BUSINESS

Organization

Histogenics Corporation (the “Company”) was incorporated under the laws of the Commonwealth of Massachusetts on June 28, 2000 and has its principal operations in Waltham, Massachusetts. In 2006, the Company’s board of directors approved a corporate reorganization pursuant to which the Company incorporated as a Delaware corporation. The Company is a regenerative medicine company engaged in developing and commercializing products in the musculoskeletal segment of the marketplace. The Company combines cell therapy and tissue engineering technologies to develop products for tissue repair and regeneration focusing on patients suffering from particular cartilage-derived pain and immobility. The Company is developing technology and products to reverse or prevent cartilage damage, including NeoCart for the repair of cartilage lesions. NeoCart is currently in a Phase 3 clinical trial in the United States under a special protocol assessment with the U.S. Food and Drug Administration (“FDA”) for the treatment of knee cartilage damage.

Since its inception, the Company has devoted substantially all of its efforts to product development, recruiting management and technical staff, raising capital, starting up production and building infrastructure and has not generated revenues from its planned principal operations. In addition, expenses have primarily been for research and development and administrative costs.

The Company is subject to a number of risks. Principal among these risks are the successful development of therapeutics, successfully enrolling patients in our clinical trials in a timely manner, protection of proprietary therapeutics, obtaining FDA approval and ongoing compliance with government regulations, ability to obtain adequate financing, fluctuations in operating results, dependence on key personnel and collaborative partners, adoption of the Company’s products by the physician community, rapid technological changes inherent in the markets targeted, and substitute products and competition from larger companies.

Initial public offering

On December 8, 2014, the Company closed its initial public offering (“IPO”) whereby the Company sold 5,909,091 shares of common stock at a price of $11.00 per share for gross proceeds of $65,000. On January 6, 2015, an additional 465,000 shares of common stock were sold at the IPO price of $11.00 per share following the underwriters’ exercise in part of their overallotment option for gross proceeds of $5,115. The shares began trading on The Nasdaq Global Market on December 3, 2014. Gross proceeds from the offering, inclusive of the overallotment, were $70,115. After giving effect to underwriting discounts and commissions and offering expenses payable by the Company, net proceeds were $61,277. In addition, each of the following occurred in connection with the completion of the IPO on December 8, 2014:

•

the conversion of all outstanding shares of the Company’s convertible redeemable preferred stock and accrued dividends into 5,158,407 shares of common stock;

•

the conversion of $11,100 in convertible notes payable and accrued interest into 1,009,115 shares of common stock;

•

the net exercise of certain warrants into 44,531 shares of common stock and the surrender of 5,839 warrant shares to satisfy the contingent payment payable to Purpose Co., Ltd. (“Other Liability”), resulting in the settlement of the related warrant liability and Other Liability upon the closing of the IPO of $490 and $612, respectively, to additional paid-in capital;

•

the termination of the redemption provision of the net sales distribution payment; and

•

the Company is now authorized to issue 100,000,000 shares of common stock and 10,000,000 shares of preferred stock.

Basis of Presentation and Principles of Consolidation

The condensed consolidated financial statements are unaudited and have been prepared in conformity with accounting principles generally accepted in the United States of America (“U.S. GAAP”) for interim financial reporting. Accordingly, they do not include all of the information and footnotes required by GAAP for complete financial statements. These interim condensed consolidated financial statements, in the opinion of the Company’s management, reflect all normal recurring adjustments necessary for a fair presentation of the Company’s financial position and results of operations for the interim periods ended March 31, 2015 and 2014. The results of operations for the interim periods are not necessarily indicative of the results of operations to be expected for the full year. These interim financial statements should be read in conjunction with the audited financial statements as of and for the year ended December 31, 2014, and the notes thereto, which are included in the Company’s Annual Report on Form 10-K filed with the Securities and Exchange Commission (the “SEC”) on March 27, 2015.

The condensed consolidated financial statements include the accounts of Histogenics Corporation and its wholly-owned subsidiaries, ProChon Biotech Ltd. (“ProChon”) and Histogenics Securities Corporation. All significant intercompany accounts and transactions are eliminated in consolidation.

Summary of Significant Accounting Policies

3 Months Ended

Mar. 31, 2015

Accounting Policies [Abstract]

Summary of Significant Accounting Policies

2. SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES

The significant accounting policies described in the Company’s audited financial statements as of and for the year ended December 31, 2014, and the notes thereto, which are included in the Annual Report on Form 10-K, have had no material changes during the three months ended March 31, 2015, except as noted below.

Reclassifications

The Company has reclassified certain prior period amounts to conform to the current period presentation. The amounts reclassified impact research and development expenses and general and administrative expenses for the three months ended March 31, 2014.

Segment and Geographic Information

Information about the Company’s operations in different geographic regions is presented in the tables below:


	March 31,		December 31,
	2015		2014
Long-lived assets:
United States	$	5,411	$	4,866
Israel		11		12

Total long-lived assets	$	5,422	$	4,878

Fair Value Measurements

The carrying amounts reported in the Company’s condensed consolidated financial statements for cash and cash equivalents, accounts payable and accrued liabilities approximate their respective fair values because of the short-term nature of these accounts.

As a basis for determining the fair value of certain of the Company’s financial instruments, the Company utilizes a three-tier value hierarchy, which prioritizes the inputs used in measuring fair value as follows:

Level 1: Unadjusted quoted prices in active markets that are accessible at the measurement date of identical, unrestricted assets.

Level 2: Quoted prices for similar assets, or inputs that are observable, either directly or indirectly, for substantially the full term through corroboration with observable market data. Level 2 includes investments valued at quoted prices adjusted for legal or contractual restrictions specific to the security.

Level 3: Pricing inputs are unobservable for the assets, that is, inputs that reflect the reporting entity’s own assumptions about the assumptions market participants would use in pricing the assets. Level 3 includes private investments that are supported by little or no market activity.

Level 3 valuations are for instruments that are not traded in active markets or are subject to transfer restrictions and may be adjusted to reflect illiquidity and/or non-transferability, with such adjustment generally based on available market evidence. In the absence of such evidence, management’s best estimate is used.

The Company had no assets or liabilities classified as Level 1 or Level 2 as of March 31, 2015 and December 31, 2014, other than the money market fund described in the “Cash and Cash Equivalents” section below, and there were no material re-measurements of fair value with respect to financial assets and liabilities during the periods presented, other than those assets and liabilities that are measured at fair value on a recurring basis. The Company had no assets or liabilities classified as Level 3 as of March 31, 2015 and December 31, 2014. Historically, the Company did have liabilities classified as Level 3 including a warrant liability, the “Other Liability” and the net sales distribution payment liability. These were all settled or terminated upon the closing of the IPO in December 2014.

Transfers are calculated on values as of the transfer date. There were no transfers between Levels 1, 2 and 3 during the three months ended March 31, 2015 and 2014.

The Company has no liabilities classified as Level 3 that are measured by management at fair value on a quarterly basis as of March 31, 2015.

Cash and Cash Equivalents

The Company’s cash equivalents, which consist of money market funds, are measured at fair value on a recurring basis based on quoted market prices.


			Quoted prices in active markets (Level 1)		Significant other observable inputs (Level 2)		Significant unobservable inputs (Level 3)


Description	Total
March 31, 2015
Money market	$	49,750	$	49,750	$	—	$	—

	$	49,750	$	49,750	$	—	$	—

December 31, 2014
Money market	$	49,750	$	49,750	$	—

	$	49,750	$	49,750	$	—	$	—

Intangible Asset

As of March 31, 2015 and December 31, 2014, the Company’s intangible asset consists of acquired in-process research and development (“IPR&D”).

For the three months ended March 31, 2015 and 2014, the Company determined that there were no triggering events indicating impairment of its IPR&D.

Intangible assets, net of accumulated impairment charges, are summarized as follows:


	As of March 31, 2015							As of December 31, 2014
			Accumulated			Net Book				Accumulated			Net Book
	Cost		Impairment			Value		Cost		Impairment			Value
IPR&D	$	630	$	(120	)	$	510	$	630	$	(120	)	$	510

	$	630	$	(120	)	$	510	$	630	$	(120	)	$	510

Stock-Based Compensation

The Company accounts for grants of stock options and restricted stock based on their grant date fair value and recognizes compensation expense on a straight-line basis over their vesting period. The Company estimates the fair value of stock options as of the date of grant using the Black-Scholes option pricing model, with the exception of stock options that include a market condition, and restricted stock based on the fair value of the underlying common stock as determined by management or the value of the services provided, whichever is more readily determinable. The expense is adjusted for actual forfeitures at year end. Stock-based compensation expense recognized in the condensed consolidated financial statements is based on awards that are ultimately expected to vest. Stock-based compensation expense is classified as research and development or general and administrative based on the grantee’s respective compensation classification.

For stock option grants with vesting triggered by the achievement of performance-based milestones, the expense is recorded over the remaining service period after the point when the achievement of the milestone is probable or the performance condition has been achieved. For stock option grants with both performance-based milestones and market conditions, expense is recorded over the derived service period after the point when the achievement of the performance-based milestone is probable or the performance condition has been achieved. For stock option grants with market conditions, expense is the grant date fair value of the option and is recorded on a straight line basis over the requisite service period, which represents the derived service period and accelerated when the market condition is satisfied. Stock options with market conditions are valued using the Monte Carlo model. The Company issued awards with market conditions during the three months ended March 31, 2015.

The Company accounts for stock options and restricted stock awards to non-employees using the fair value approach. Stock options and restricted stock awards to non-employees are subject to periodic revaluation over their vesting terms.

Recent Accounting Pronouncements

There are no recent accounting standards that would impact the results reported in the unaudited condensed consolidated interim financial statements.

Loss Per Common Share

3 Months Ended

Mar. 31, 2015

Earnings Per Share [Abstract]

Loss Per Common Share

3. LOSS PER COMMON SHARE

The Company computes basic and diluted loss per share using a methodology that gives effect to the impact of outstanding participating securities (the “two-class method”). As the three month periods ended March 31, 2015 and 2014 resulted in net losses, there is no income allocation required under the two-class method or dilution attributed to the weighted-average shares outstanding in the calculated of diluted loss per share.

The following potentially dilutive securities have been excluded from the computation of diluted weighted-average shares outstanding, as they would be anti-dilutive (in common stock equivalent shares):


	Three Months Ended March 31,
	2015		2014
Convertible redeemable preferred stock and dividends		—		3,603,308
Restricted stock and options to purchase common stock		842,492		287,711
Warrants exercisable into common stock		170,102		161,977

The Company also had certain warrants and other liabilities outstanding as of March 31, 2014 which could have obligated the Company, its stockholders, or both to issue shares of common stock upon the occurrence of various future events at prices and in amounts that were not determinable until the occurrence of those future events. For the three months ended March 31, 2014, these included the net sales distribution payment liability. Because the necessary conditions for the conversion or exercise of these instruments had not been satisfied as of March 31, 2014, the Company has excluded these instruments from the table above and the calculation of diluted net income per share for that period.

Property and Equipment

3 Months Ended

Mar. 31, 2015

Property, Plant and Equipment [Abstract]

Property and Equipment

4. PROPERTY AND EQUIPMENT

Property and equipment consisted of the following:


	March 31,			December 31,
	2015			2014
Office equipment	$	504		$	467
Laboratory equipment		3,925			2,978
Leasehold improvements		7,644			7,503
Construction in progress		—			270
Software		96			35

Total property and equipment		12,169			11,253
less: accumulated depreciation		(6,747	)		(6,375	)

Property and equipment, net	$	5,422		$	4,878

Depreciation expense related to property and equipment amounted to $371 and $153 for the three months ended March 31, 2015 and 2014, respectively.

Commitments and Contingencies

3 Months Ended

Mar. 31, 2015

Commitments and Contingencies Disclosure [Abstract]

Commitments and Contingencies

5. COMMITMENTS AND CONTINGENCIES

Operating Leases

The Company leases its office and research facilities in Waltham, Massachusetts under a non-cancellable operating lease that expires in 2017. Terms of the agreement provide for an initial rent-free period and future rent escalation, and provide that in addition to minimum lease rental payments, the Company is responsible for a pro-rata share of common area operating expenses. In January 2014, the Company entered into an agreement with a third party to sublease an additional facility in Waltham, Massachusetts. The term of the sublease extends from February 1, 2014 through July 30, 2015. In June 2014, the Company entered into a lease agreement to rent a facility in Lexington, Massachusetts. The commencement date of the lease was July 9, 2014 with a term that extends through June 1, 2023. Terms of the lease agreement provide for an initial rent-free period and future rent escalation, and provide that in addition to minimum lease rental payments, the Company is responsible for a pro-rata share of operating expenses. The Company’s wholly-owned subsidiary, ProChon, leases facilities in Woburn, Massachusetts and Israel.

Rent expense under operating lease agreements amounted to approximately $291 and $151 for the three months ended March 31, 2015 and 2014, respectively. In addition, the Company maintained a stand-by letter of credit in connection with the Waltham facility lease of $467 at March 31, 2015 and December 31, 2014. The Company also maintained a stand-by letter of credit in connection with the Lexington facility lease of $137 at March 31, 2015 and December 31, 2014. These amounts are classified as restricted cash in the condensed consolidated balance sheets.

As an inducement to enter into its Waltham facility lease, the lessor agreed to provide the Company with a construction allowance of up to $3,184 towards the total cost of tenant improvements. The Company has recorded these costs in the condensed consolidated balance sheet as leasehold improvements, with the corresponding liability as deferred lease incentive. This liability is amortized on a straight-line basis over the term of the lease as a reduction of rent expense.

As an inducement to enter into its Lexington facility lease, the lessor agreed to provide the Company with a construction allowance of up to $996 towards the total cost of tenant improvements. The tenant improvement is recorded within leasehold improvements and included as a deferred lease incentive liability in the condensed consolidated balance sheet. Rent expense is recognized on a straight-line basis over the term of the lease and is reduced by the construction allowance.

License Agreements

From time to time, the Company enters into various licensing agreements whereby the Company may use certain technologies in conjunction with its product research and development.

Licensing agreements and the Company’s commitments under the agreements are as follows:

Hydrogel License

In May 2005, the Company entered into an exclusive license agreement with Angiotech Pharmaceuticals (US), Inc. for the use of certain patents, patent application, and knowledge related to the manufacture and use of a hydrogel material in conjunction with NeoCart and certain other products (“Hydrogel License Agreement”). As of March 31, 2015, the Company has paid an aggregate $3,200 in commercialization milestones under the terms of the Hydrogel License Agreement, which have been expensed to research and development.

Under the terms of the Hydrogel License Agreement, the Company’s future commitments include:

•

A one-time $3,000 payment upon approval of an eligible product by the FDA; and

•

Royalties in the single digits of the net sales of NeoCart and of certain other future products.

Tissue Regeneration License

In April 2001, the Company entered into an exclusive license agreement with The Board of Trustees of the Leland Stanford Junior University (“Stanford University”) for the use of certain technology to develop, manufacture and sell licensed products in the field of growth and regeneration of cartilage (“Tissue Regeneration License Agreement”). The length of the license agreement extends to the expiration date of Stanford University’s last to expire domestic or foreign patents as set forth in the Tissue Regeneration License Agreement. As of March 31, 2015, the Company has paid an aggregate $640 in patent reimbursement costs, royalty fees, and commercialization milestone payments under the terms of the Tissue Regeneration License Agreement, which have been recorded to research and development expense.

Under the terms of the Tissue Regeneration License Agreement, the Company’s future commitments include:

•

A one-time $300 payment upon approval of an eligible product by the FDA;

•

An annual minimum non-refundable royalty fee of $10 for the life of the license that may be used to offset up to 50% of each earned royalty described below; and

•

Royalties in the low single digits of net sales.

Honeycomb License

In March 2013, the Company entered into a license agreement with Koken Co., Ltd. (“Koken”) and paid a fee for a non-exclusive, non-transferable and non-sublicensable right to use its know-how related to the process for manufacturing atelocollagen honeycomb sponge materials, which is used in scaffolds (the “Honeycomb License Agreement”). Under the terms of the Honeycomb License Agreement, future commitments will be based on the amount of materials supplied to the Company and may vary from period to period over the term of the agreement.

Plasmid License

In January 2008, the Company entered into an exclusive license agreement with Yeda Research and Development Co., Ltd. (“Yeda”) for rights relating to high level expression of heterologous proteins and plasmid p80 BS (the “Plasmid License Agreement”), which rights are jointly owned by Yeda and the Company. Under the terms of the Plasmid License Agreement, the Company was granted an exclusive worldwide license to manufacture, use and sell heterologous proteins and plasmid p80 BS.

The Company is required to pay Yeda a yearly, non-refundable license fee of $2, which is creditable against royalties payable by the Company to Yeda during the one-year period in which such fee was paid. Yeda is entitled a royalty fee of a low single digit percentage of net sales of the licensed products and of net sales for combination products (meaning the combination of the licensed product with at least one other active ingredient, material or medical device that would have a clinical effect if administered independently) and a low double digit percentage of all of the Company’s sublicensing receipts.

Tissue Processor Sub-License

In December 2005, the Company entered into an exclusive agreement to sub-license certain technology from Purpose, Co. (“Purpose”), which is owned by a stockholder of the Company (“Sub-License Agreement”). The original license agreement (“Original Agreement”) was entered into in August 2001 with Brigham and Women’s Hospital, Inc. (“Brigham and Women’s”). The Original Agreement shall remain in effect for the licensed patents owned by Brigham and Women’s unless extended or terminated as provided for in the agreement. The technology is to be used to develop, manufacture, use and sell licensed products that cultivate cell or tissue development. The Sub-License Agreement extends to the expiration date of the last to expire domestic or foreign patents covered by the agreement. As of March 31, 2015, the Company has paid an aggregate $941 over the term of the Sub-License Agreement in royalty and sub-license payments under the terms of the Sub-License Agreement, which was recorded to research and development expense in the condensed consolidated statements of operations.

The Sub-License Agreement was amended and restated in June 2012. Under the amended and restated agreement, the Company made Purpose, the sole supplier of equipment, which the Company uses in its manufacturing processes, and granted Purpose distribution rights of the Company’s products for certain territories. In exchange, Purpose allowed for the use of its technology (owned or licensed) and manufactured and serviced exogenous tissue processors by the Company. Under the terms of the agreement, as amended, Purpose granted the Company (a) exclusive rights to all of Purpose’s technology (owned or licensed) related to the exogenous tissue processors, (b) continued supply of exogenous tissue processors during the Company’s clinical trials, and (c) rights to manufacture the exogenous tissue processors at any location the Company chooses. In exchange for such consideration, the Company granted Purpose an exclusive license in Japan for the use of all of the Company’s technology and a payment of $250 to reimburse Purpose for development costs on a next generation tissue processer.

In addition to the above, the Company’s future commitments under the terms of the Original Agreement and Sub-License Agreement include:

•

A minimum non-refundable annual royalty fee of $20, for the life of the license;

•

$200 in milestone payments; and

•

Royalties in the low single digits of net sales of a licensed product.

The OCS Agreement

In connection with its research and development, the Company received grants from the Office of Chief Scientist of the Ministry of Industry and Trade in Israel (“OCS”) in the aggregate of $1,100 for funding the fibroblast growth factor (“FGF”) program. In consideration for this grant, the Company is committed to pay royalties at a rate of 3% to 5% of the sales of sponsored products developed using the grant money, up to the amount of the participation payments received. The Company committed to pay up to 100% of grants received plus interest according to the LIBOR interest rate if the sponsored product is produced in Israel. If the manufacturing of the sponsored product takes place outside of Israel, the royalties can increase up to but no more than 300% of grants received plus interest based on the LIBOR interest rate, depending on the percentage of the manufacturing of sponsored product that takes place outside of Israel.

Engineering Agreement

The Company entered into an agreement with a development corporation to purchase a multi-unit bioreactor system. Pursuant to the agreement, the Company will be required to make payments totaling $567, which are comprised of a deposit of $150 paid in May 2013 with the remaining $417 to be paid upon the Company’s acceptance of the delivery of the system, which is expected in 2015.

Warrants	3 Months Ended
Warrants	Mar. 31, 2015
Text Block [Abstract]
Warrants	6. WARRANTS Consulting Agreement Warrant In March 2015, in connection with a consulting agreement entered into for an interim chief financial officer, the Company issued a common stock warrant as compensation to the consulting firm. The warrant provides the holder with the right to purchase an aggregate of 7,398 shares of the Company’s common stock at a per share exercise price of $9.75, the closing price of the Company’s common stock on the date of issuance. The warrant vests and becomes exercisable in monthly installments over 24 months beginning March 31, 2015. The warrant expires on the tenth anniversary of issuance. The warrant is equity classified and accounted for using the fair value approach and is subject to periodic revaluation over the vesting term. The equity-classified warrant issued in March 2015 was valued using the Black-Scholes option pricing model (“OM”) and is subject to re-measurement at each reporting period until the measurement date is reached. Expense is recognized to general and administrative expenses on a straight-line basis over the expected service period, which is the vesting period. Affiliates of an Advisor Warrant In connection with the issuance of the Series A Preferred on July 20, 2012, the Company issued a warrant to purchase its common stock to affiliates of an advisor. The warrant provides the holders with the right to purchase an aggregate of 161,977 shares of the Company’s common stock at a per share exercise price of $0.01. The warrants are exercisable, in whole or in part, immediately upon issuance and may be exercised on a cashless basis. The warrants expire on the tenth anniversary of issuance. The fair value of the warrants as of July 20, 2012 was estimated using the OM. with the following inputs: (a) risk-free interest rate of 0.22%; (b) implied volatility of the Company’s common stock of 99%; and (c) the expected term to a liquidity event of 1.7 years. The fair value of the warrants as of July 20, 2012 was $117, which was recorded as a reduction to Series A Preferred and a credit to additional paid-in capital. On December 8, 2014, the Company completed its IPO and warrants for 5,839 shares of common stock were surrendered to partially settle the Other Liability and common stock was issued by the Company to Purpose for the warrant shares surrendered. As of March 31, 2015 and December 31, 2014, warrants to purchase an aggregate of 156,138 shares of the Company’s common stock at an exercise price of $0.01 are outstanding. Equipment Loan Warrant On July 9, 2014, the Company entered into a loan and security agreement with Silicon Valley Bank for a loan to purchase equipment. The amount of the loan is $1,750 and bears interest at prime plus 2.75%, or 6.00% at each funding date, and is payable in equal monthly installments over 36 months beginning six months after the funding date, which ranged from August 2014 to November 2014. The Company granted Silicon Valley Bank a warrant to purchase 6,566 shares of common stock at a per share exercise price of $7.99 in connection with entering into the loan and security agreement. The warrant is exercisable, in whole or in part, immediately upon issuance and may be exercised on a cashless basis and expires on the tenth anniversary of issuance. The fair value of the warrant as of July 9, 2014 was estimated at $51 with the following inputs: (a) risk-free interest rate of 2.58%; (b) implied volatility of the Company’s common stock of 87%; (c) the expected term of 10 years. The fair value of the warrant was recorded as a debt issuance cost with a corresponding credit to additional paid-in capital.

Stock-Based Compensation

3 Months Ended

Mar. 31, 2015

Disclosure of Compensation Related Costs, Share-based Payments [Abstract]

Stock-Based Compensation

7. STOCK-BASED COMPENSATION

Stock option activity under the Company’s 2012 Equity Incentive Plan (the “2012 Plan”) and 2013 Equity Incentive Plan (the “2013 Plan”) for the three months ended March 31, 2015 is summarized as follows:


	Number of Options			Weighted- Average Exercise Price		Weighted- Average Remaining Contractual Term (in years)		Aggregate Intrinsic Value (in thousands)
Outstanding at December 31, 2014		537,683		$	6.19
Granted		389,050
Cancelled		(92,734	)

Outstanding at March 31, 2015		833,999		$	7.71		9.2	$	1,814


Vested and expected to vest at March 31, 2015		769,853		$	7.55		9.1	$	1,879


Exercisable at March 31, 2015		180,198		$	2.43		7.9	$	1,362

As of March 31, 2015, the unrecognized compensation cost related to outstanding options was $3,615 and is expected to be recognized as expense over approximately 2.98 years. As of March 31, 2015, the weighted average grant date fair value of vested options was $2.05 and the weighted average grant date fair value of shares outstanding was $5.16.

For the three months ended March 31, 2015, the weighted average grant date fair value per share of employee option grants within the period was $4.51. There were no option grants for the three months ended March 31, 2014. No options were exercised for the three months ended March 31, 2015 or March 31, 2014.

Restricted stock awards under the 2012 Plan and 2013 Plan for the three months ended March 31, 2015 are summarized as follows:


	Number of Shares		Weighted-Average Grant Date Fair Value
Unvested at December 31, 2014		8,493	$	1.04

Unvested at March 31, 2015		8,493	$	1.04

As of March 31, 2015, the unrecognized compensation cost related to restricted stock awards was $6 and is expected to be recognized as expense over approximately 1.91 years.

Stock-Based Compensation Expense

The Company granted stock options to employees for the three months ended March 31, 2015 and 2014. The Company estimates the fair value of stock options as of the date of grant using the Black-Scholes option pricing model and restricted stock based on the stock price, with the exception of those stock options that included a market condition. The Company estimates the fair value of stock options that include a market condition using the Monte-Carlo model. Stock options and restricted stock issued to non-board member, non-employees are accounted for using the fair value approach and are subject to periodic revaluation over their vesting terms.

Stock compensation expense amounted to $235 and $76 for the three months ended March 31, 2015 and 2014, respectively.

The allocation of stock-based compensation for all options granted and restricted stock awards are as follows:


	Three Months Ended March 31,
	2015		2014
Research and development	$	100	$	27
General and administrative		135		49

Total stock-based compensation expense	$	235	$	76

Stock-based compensation by award type is as follows:


	Three Months Ended March 31,
	2015		2014
Stock options	$	234	$	75
Restricted stock		1		1

Total stock-based compensation expense	$	235	$	76

The weighted-average assumptions used in the Black-Scholes option pricing model to determine the fair value of the employee stock option grants were as follows:


	Three Months Ended March 31,
	2015			2014
Risk-free interest rate		1.60	%		1.01	%
Expected volatility		65.8	%		87.9	%
Expected term (in years)		6.09			5.36
Expected dividend yield		0.0	%		0.0	%

The weighted-average assumptions used in the Black-Scholes option pricing model to determine the fair value of the non-employee stock option grants were as follows:


	Three Months Ended March 31,
	2015			2014
Risk-free interest rate		0.56	%		0.57	%
Expected volatility		59.7	%		109.9	%
Expected term (in years)		2.22			2.13
Expected dividend yield		0.0	%		0.0	%

Income Taxes	3 Months Ended
Income Taxes	Mar. 31, 2015
Income Tax Disclosure [Abstract]
Income Taxes	8. INCOME TAXES Deferred tax assets and deferred tax liabilities are recognized based on temporary differences between the financial reporting and tax basis of assets and liabilities using statutory rates. A valuation allowance is recorded against deferred tax assets if it is more likely than not that some or all of the deferred tax assets will not be realized. Due to the uncertainty surrounding the realization of the favorable tax attributes in future tax returns, the Company has recorded a full valuation allowance against the Company’s otherwise recognizable net deferred tax assets. The Company has allocated its valuation allowance in accordance with the provisions of ASC 740, Income Taxes, which resulted in a non-current deferred tax asset of $1,034 and a current deferred tax liability of $1,034 as of March 31, 2015.

Summary of Significant Accounting Policies (Policies)

3 Months Ended

Mar. 31, 2015

Accounting Policies [Abstract]

Reclassifications

Reclassifications

Segment and Geographic Information

Segment and Geographic Information

Information about the Company’s operations in different geographic regions is presented in the tables below:


	March 31,		December 31,
	2015		2014
Long-lived assets:
United States	$	5,411	$	4,866
Israel		11		12

Total long-lived assets	$	5,422	$	4,878

Fair Value Measurements

Fair Value Measurements

Level 1: Unadjusted quoted prices in active markets that are accessible at the measurement date of identical, unrestricted assets.

Transfers are calculated on values as of the transfer date. There were no transfers between Levels 1, 2 and 3 during the three months ended March 31, 2015 and 2014.

The Company has no liabilities classified as Level 3 that are measured by management at fair value on a quarterly basis as of March 31, 2015.

Cash and Cash Equivalents

Cash and Cash Equivalents

The Company’s cash equivalents, which consist of money market funds, are measured at fair value on a recurring basis based on quoted market prices.


			Quoted prices in active markets (Level 1)		Significant other observable inputs (Level 2)		Significant unobservable inputs (Level 3)


Description	Total
March 31, 2015
Money market	$	49,750	$	49,750	$	—	$	—

	$	49,750	$	49,750	$	—	$	—

December 31, 2014
Money market	$	49,750	$	49,750	$	—

	$	49,750	$	49,750	$	—	$	—

Intangible Assets

Intangible Asset

As of March 31, 2015 and December 31, 2014, the Company’s intangible asset consists of acquired in-process research and development (“IPR&D”).

For the three months ended March 31, 2015 and 2014, the Company determined that there were no triggering events indicating impairment of its IPR&D.

Intangible assets, net of accumulated impairment charges, are summarized as follows:


	As of March 31, 2015							As of December 31, 2014
			Accumulated			Net Book				Accumulated			Net Book
	Cost		Impairment			Value		Cost		Impairment			Value
IPR&D	$	630	$	(120	)	$	510	$	630	$	(120	)	$	510

	$	630	$	(120	)	$	510	$	630	$	(120	)	$	510

Stock-Based Compensation

Stock-Based Compensation

Recent Accounting Pronouncements

Recent Accounting Pronouncements

There are no recent accounting standards that would impact the results reported in the unaudited condensed consolidated interim financial statements.

- Definition

Disclosure of accounting policy for cash and cash equivalents, including the policy for determining which items are treated as cash equivalents. Other information that may be disclosed includes (1) the nature of any restrictions on the entity's use of its cash and cash equivalents, (2) whether the entity's cash and cash equivalents are insured or expose the entity to credit risk, (3) the classification of any negative balance accounts (overdrafts), and (4) the carrying basis of cash equivalents (for example, at cost) and whether the carrying amount of cash equivalents approximates fair value.

+ References + Details

Summary of Significant Accounting Policies (Tables)

3 Months Ended

Mar. 31, 2015

Accounting Policies [Abstract]

Summary of Operations in Different Geographic Regions

Information about the Company’s operations in different geographic regions is presented in the tables below:


	March 31,		December 31,
	2015		2014
Long-lived assets:
United States	$	5,411	$	4,866
Israel		11		12

Total long-lived assets	$	5,422	$	4,878

Summary of Cash Equivalents Measured at Fair Value on Recurring Basis

The Company’s cash equivalents, which consist of money market funds, are measured at fair value on a recurring basis based on quoted market prices.


			Quoted prices in active markets (Level 1)		Significant other observable inputs (Level 2)		Significant unobservable inputs (Level 3)


Description	Total
March 31, 2015
Money market	$	49,750	$	49,750	$	—	$	—

	$	49,750	$	49,750	$	—	$	—

December 31, 2014
Money market	$	49,750	$	49,750	$	—

	$	49,750	$	49,750	$	—	$	—

Summary of Intangible Assets, Net of Accumulated Impairment Charges

Intangible assets, net of accumulated impairment charges, are summarized as follows:


	As of March 31, 2015							As of December 31, 2014
			Accumulated			Net Book				Accumulated			Net Book
	Cost		Impairment			Value		Cost		Impairment			Value
IPR&D	$	630	$	(120	)	$	510	$	630	$	(120	)	$	510

	$	630	$	(120	)	$	510	$	630	$	(120	)	$	510

Loss Per Common Share (Tables)

3 Months Ended

Mar. 31, 2015

Earnings Per Share [Abstract]

Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share


	Three Months Ended March 31,
	2015		2014
Convertible redeemable preferred stock and dividends		—		3,603,308
Restricted stock and options to purchase common stock		842,492		287,711
Warrants exercisable into common stock		170,102		161,977

Property and Equipment (Tables)

3 Months Ended

Mar. 31, 2015

Property, Plant and Equipment [Abstract]

Schedule of Property and Equipment

Property and equipment consisted of the following:


	March 31,			December 31,
	2015			2014
Office equipment	$	504		$	467
Laboratory equipment		3,925			2,978
Leasehold improvements		7,644			7,503
Construction in progress		—			270
Software		96			35

Total property and equipment		12,169			11,253
less: accumulated depreciation		(6,747	)		(6,375	)

Property and equipment, net	$	5,422		$	4,878

Stock-Based Compensation (Tables)

3 Months Ended

Mar. 31, 2015

Disclosure of Compensation Related Costs, Share-based Payments [Abstract]

Summary of Stock Option Activity Under the 2012 and 2013 Plans


	Number of Options			Weighted- Average Exercise Price		Weighted- Average Remaining Contractual Term (in years)		Aggregate Intrinsic Value (in thousands)
Outstanding at December 31, 2014		537,683		$	6.19
Granted		389,050
Cancelled		(92,734	)

Outstanding at March 31, 2015		833,999		$	7.71		9.2	$	1,814


Vested and expected to vest at March 31, 2015		769,853		$	7.55		9.1	$	1,879


Exercisable at March 31, 2015		180,198		$	2.43		7.9	$	1,362

Schedule of Restricted Stock Awards Under the 2012 and 2013 Plans

Restricted stock awards under the 2012 Plan and 2013 Plan for the three months ended March 31, 2015 are summarized as follows:


	Number of Shares		Weighted-Average Grant Date Fair Value
Unvested at December 31, 2014		8,493	$	1.04

Unvested at March 31, 2015		8,493	$	1.04

Summary of Stock-Based Compensation for All Options Granted and Restricted Stock Awards

The allocation of stock-based compensation for all options granted and restricted stock awards are as follows:


	Three Months Ended March 31,
	2015		2014
Research and development	$	100	$	27
General and administrative		135		49

Total stock-based compensation expense	$	235	$	76

Summary of Stock-Based Compensation by Award

Stock-based compensation by award type is as follows:


	Three Months Ended March 31,
	2015		2014
Stock options	$	234	$	75
Restricted stock		1		1

Total stock-based compensation expense	$	235	$	76

Summary of Weighted-Average Assumptions Used in the Black-Scholes Option Pricing Model to Determine the Fair Value of the Employee Stock Option Grants

The weighted-average assumptions used in the Black-Scholes option pricing model to determine the fair value of the employee stock option grants were as follows:


	Three Months Ended March 31,
	2015			2014
Risk-free interest rate		1.60	%		1.01	%
Expected volatility		65.8	%		87.9	%
Expected term (in years)		6.09			5.36
Expected dividend yield		0.0	%		0.0	%

Summary of Weighted-Average Assumptions Used in the Black-Scholes Option Pricing Model to Determine the Fair Value of the Non-Employee Stock Option Grants

The weighted-average assumptions used in the Black-Scholes option pricing model to determine the fair value of the non-employee stock option grants were as follows:


	Three Months Ended March 31,
	2015			2014
Risk-free interest rate		0.56	%		0.57	%
Expected volatility		59.7	%		109.9	%
Expected term (in years)		2.22			2.13
Expected dividend yield		0.0	%		0.0	%

Nature of Business - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands			3 Months Ended
	Jan. 06, 2015	Dec. 08, 2014	Mar. 31, 2015	Dec. 31, 2014
Nature Of Business And Basis Of Presentation [Line Items]
Date of incorporation			Jun. 28, 2000
Gross proceeds from initial public offering		$ 70,115
Net proceeds from initial public offering		$ 61,277
Conversion of redeemable preferred stock and accrued dividends		5,158,407
Net exercise of warrants, shares		44,531	156,138	156,138
Surrender of warrant to satisfy other liability		5,839
Additional paid-in capital			$ 192,597	$ 187,620
Common stock, shares authorized		100,000,000	100,000,000	100,000,000
Preferred stock shares authorized		10,000,000	10,000,000	10,000,000
IPO [Member]
Nature Of Business And Basis Of Presentation [Line Items]
Sale of common stock shares		5,909,091
Initial public offering price per share		$ 11.00
Gross proceeds from initial public offering		$ 65,000
Convertible notes payable to common stock		$ 11,100
Accrued interest to common stock		1,009,115
Over-Allotment Option [Member]
Nature Of Business And Basis Of Presentation [Line Items]
Sale of common stock shares	465,000
Initial public offering price per share	$ 11.00
Gross proceeds from initial public offering	$ 5,115
Warrant Liability [Member]
Nature Of Business And Basis Of Presentation [Line Items]
Additional paid-in capital		$ 490
Other Liability [Member]
Nature Of Business And Basis Of Presentation [Line Items]
Additional paid-in capital		$ 612

Summary of Significant Accounting Policies - Summary of Operations in Different Geographic Regions (Detail) - USD ($) $ in Thousands	Mar. 31, 2015	Dec. 31, 2014
Segment Reporting Information [Line Items]
Long-lived assets	$ 5,422	$ 4,878
United States [Member]
Segment Reporting Information [Line Items]
Long-lived assets	5,411	4,866
Israel [Member]
Segment Reporting Information [Line Items]
Long-lived assets	$ 11	$ 12

Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($)	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014
IPR&D [Member]
Summary Of Significant Accounting Policies [Line Items]
Impairment of intangible assets	$ 0	$ 0
Significant Unobservable Inputs (Level 3) [Member]
Summary Of Significant Accounting Policies [Line Items]
Assets, fair value disclosure, recurring	0		$ 0
Liabilities, fair value disclosure, recurring	0		0
Liabilities, fair value disclosure	0
Quoted Prices in Active Markets (Level 1) [Member]
Summary Of Significant Accounting Policies [Line Items]
Assets, fair value disclosure, recurring	0		0
Liabilities, fair value disclosure, recurring	0		0
Significant Other Observable Inputs (Level 2) [Member]
Summary Of Significant Accounting Policies [Line Items]
Assets, fair value disclosure, recurring	0		0
Liabilities, fair value disclosure, recurring	$ 0		$ 0

Summary of Significant Accounting Policies - Summary of Cash Equivalents Measured at Fair Value on Recurring Basis (Detail) - USD ($) $ in Thousands	Mar. 31, 2015	Dec. 31, 2014
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents, fair value	$ 49,750	$ 49,750
Money Market [Member]
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents, fair value	49,750	49,750
Quoted Prices in Active Markets (Level 1) [Member]
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents, fair value	49,750	49,750
Quoted Prices in Active Markets (Level 1) [Member] \| Money Market [Member]
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents, fair value	$ 49,750	$ 49,750

Summary of Significant Accounting Policies - Summary of Intangible Assets, Net of Accumulated Impairment Charges (Detail) - USD ($) $ in Thousands	Mar. 31, 2015	Dec. 31, 2014
Indefinite-lived Intangible Assets [Line Items]
Cost	$ 630	$ 630
Accumulated Impairment	(120)	(120)
Net Book Value	510
Net Book Value	510	510
IPR&D [Member]
Indefinite-lived Intangible Assets [Line Items]
Cost	630	630
Accumulated Impairment	(120)	(120)
Net Book Value	$ 510
Net Book Value		$ 510

Loss Per Common Share - Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share (Detail) - shares	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Convertible Redeemable Preferred Stock and Dividends [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of earnings per share		3,603,308
Restricted Stock and Options to Purchase Common Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of earnings per share	842,492	287,711
Warrants Exercisable into Common Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of earnings per share	170,102	161,977

Property and Equipment - Schedule of Property and Equipment (Detail) - USD ($) $ in Thousands	Mar. 31, 2015	Dec. 31, 2014
Property, Plant and Equipment [Line Items]
Total property and equipment	$ 12,169	$ 11,253
less: accumulated depreciation	(6,747)	(6,375)
Property and equipment, net	5,422	4,878
Office Equipment [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment	504	467
Laboratory Equipment [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment	3,925	2,978
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment	7,644	7,503
Construction in Progress [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment		270
Software [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment	$ 96	$ 35

Property and Equipment - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Property, Plant and Equipment [Abstract]
Depreciation expense	$ 371	$ 153

Commitments and Contingencies - Additional Information (Detail) - USD ($)	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014
Loss Contingencies [Line Items]
Rent expense under operating lease agreements	$ 291,000	$ 151,000
Research and development expense	$ (5,764,000)	$ (3,374,000)
Massachusetts [Member] \| Waltham [Member]
Loss Contingencies [Line Items]
Lease expiration period	2017
Description of lease arrangements	February 1, 2014 through July 30, 2015.
Lease expiration date	Jul. 30, 2015
Massachusetts [Member] \| Lexington [Member]
Loss Contingencies [Line Items]
Description of lease arrangements	July 9, 2014 with a term that extends through June 1, 2023.
Lease expiration date	Jun. 01, 2023
Lease commencement period	Jul. 09, 2014
Hydrogel License Agreement [Member]
Loss Contingencies [Line Items]
Research and development expense	$ 3,200,000
One-time payment amount	3,000,000
Tissue Regeneration License Agreement [Member]
Loss Contingencies [Line Items]
Research and development expense	640,000
One-time payment amount	$ 300,000
Percentage of royalty offsetting	50.00%
Plasmid License Agreement [Member]
Loss Contingencies [Line Items]
Non-refundable license fee	$ 2,000
Maximum [Member] \| Waltham [Member]
Loss Contingencies [Line Items]
Construction allowance to total cost of tenant improvements	3,184,000
Maximum [Member] \| Lexington [Member]
Loss Contingencies [Line Items]
Construction allowance to total cost of tenant improvements	996,000
Minimum [Member] \| Tissue Regeneration License Agreement [Member]
Loss Contingencies [Line Items]
Non-refundable royalty fee	10,000
Tissue Processor Sub License Agreement [Member]
Loss Contingencies [Line Items]
Research and development expense	941,000
Reimbursement for development cost	250,000
Milestone payment	200,000
Tissue Processor Sub License Agreement [Member] \| Minimum [Member]
Loss Contingencies [Line Items]
Non-refundable royalty fee	20,000
OCS Agreement [Member]
Loss Contingencies [Line Items]
Accrued and received grants, aggregate	$ 1,100,000
OCS Agreement [Member] \| Maximum [Member]
Loss Contingencies [Line Items]
Royalties payment, rate	5.00%
Royalty payment percentage as percentage of grant received	300.00%
OCS Agreement [Member] \| Minimum [Member]
Loss Contingencies [Line Items]
Royalties payment, rate	3.00%
Royalty payment percentage as percentage of grant received	100.00%
Stand-By Letter of Credit [Member] \| Waltham [Member]
Loss Contingencies [Line Items]
Stand-by letter of credit maintained by company	$ 467,000		$ 467,000
Stand-By Letter of Credit [Member] \| Lexington [Member]
Loss Contingencies [Line Items]
Stand-by letter of credit maintained by company	137,000		$ 137,000
Engineering Agreement [Member]
Loss Contingencies [Line Items]
Total purchase amount of multi-unit bracketed system	567,000
Purchase commitment deposit paid	150,000
Purchase amount, remaining to be paid	$ 417,000

Warrants - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands				3 Months Ended
	Dec. 08, 2014	Jul. 09, 2014	Jul. 20, 2012	Mar. 31, 2015	Dec. 31, 2014
Class of Warrant or Right [Line Items]
Class of Warrants or right to purchase common stock	44,531			156,138	156,138
Class of Warrants or right to purchase common stock, exercise price				$ 0.01	$ 0.01
Warrants expiry period			10 years
Fair value of the warrants, risk free interest rate			0.22%
Fair value of the warrants, implied volatility			99.00%
Fair value of the warrants, expected term to liquidity			1 year 8 months 12 days
Fair value of warrants			$ 117
Common stock surrendered	5,839
Silicon Valley Bank Loan and Security Agreement [Member]
Class of Warrant or Right [Line Items]
Bank loan and security agreement, amount		$ 1,750
Bank loan and security agreement, Interest at prime		6.00%
Bank loan and security agreement, repayment period		36 months
Silicon Valley Bank [Member]
Class of Warrant or Right [Line Items]
Class of Warrants or right to purchase common stock				6,566
Class of Warrants or right to purchase common stock, exercise price				$ 7.99
Warrants expiry period				10 years
Fair value of the warrants, risk free interest rate		2.58%
Fair value of the warrants, implied volatility		87.00%
Fair value of the warrants, expected term to liquidity		10 years
Fair value of warrants		$ 51
Prime Rate [Member] \| Silicon Valley Bank Loan and Security Agreement [Member]
Class of Warrant or Right [Line Items]
Bank loan and security agreement, Interest at prime		2.75%
Series A Preferred Stock [Member]
Class of Warrant or Right [Line Items]
Class of Warrants or right to purchase common stock			161,977
Class of Warrants or right to purchase common stock, exercise price			$ 0.01
Consulting Agreement Warrant [Member]
Class of Warrant or Right [Line Items]
Class of Warrants or right to purchase common stock				7,398
Class of Warrants or right to purchase common stock, exercise price				$ 9.75
Warrants exercisable period				24 months
Warrants expiry period				10 years

Stock-Based Compensation - Summary of Stock Option Activity Under the 2012 and 2013 Plans (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Number of Options, Outstanding Beginning Balance	537,683
Number of Options, Granted	389,050	0
Number of Options, Cancelled	(92,734)
Number of Options, Outstanding Ending Balance	833,999
Number of Options, Vested and expected to vest outstanding	769,853
Number of Options, Exercisable	180,198
Weighted Average Exercise Price, Outstanding Beginning Balance	$ 6.19
Weighted Average Exercise Price, Granted	0
Weighted Average Exercise Price, Cancelled	0
Weighted Average Exercise Price, Outstanding Ending Balance	7.71
Weighted Average Exercise Price, Vested and expected to vest outstanding	7.55
Weighted Average Exercise Price, Exercisable	$ 2.43
Weighted Average Remaining Contractual Term, Outstanding	9 years 2 months 12 days
Weighted Average Remaining Contractual Term, Vested and expected to vest outstanding	9 years 1 month 6 days
Weighted Average Remaining Contractual Term, Exercisable	7 years 10 months 24 days
Aggregate Intrinsic Value, Outstanding	$ 1,814
Aggregate Intrinsic Value, Vested and expected to vest outstanding	1,879
Aggregate Intrinsic Value, Exercisable	$ 1,362

Stock-Based Compensation - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation cost related to outstanding options	$ 3,615
Weighted average grant date fair value of vested options	$ 2.05
Weighted average grant date fair value of shares outstanding	5.16
Weighted average grant date fair value per share of employee option granted	$ 4.51
Share-based compensation award, number of options granted	389,050	0
Share-based compensation award, options exercised	0	0
Stock-based compensation expense	$ 235	$ 76
Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation cost, recognition period	2 years 11 months 23 days
Stock-based compensation expense	$ 234	75
Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation cost, recognition period	1 year 10 months 28 days
Unrecognized compensation cost related to restricted stock awards	$ 6
Stock-based compensation expense	$ 1	$ 1

Stock-Based Compensation - Schedule of Restricted Stock Awards Under the 2012 and 2013 Plans (Detail) - Restricted Stock [Member]	Mar. 31, 2015 $ / shares shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares, Unvested beginning balance \| shares	8,493
Number of shares, Unvested ending balance \| shares	8,493
Weighted-average grant date fair value, Unvested beginning balance \| $ / shares	$ 1.04
Weighted-average grant date fair value, Unvested ending balance \| $ / shares	$ 1.04

Stock-Based Compensation - Summary of Stock-Based Compensation for all Options Granted and Restricted Stock Awards (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	$ 235	$ 76
Research and Development [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	100	27
General and Administrative [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	$ 135	$ 49

Stock-Based Compensation - Summary of Stock-Based Compensation by Award (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Restricted stock	$ 235	$ 76
Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Restricted stock	234	75
Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Restricted stock	$ 1	$ 1

Stock-Based Compensation - Summary of Weighted-Average Assumptions Used in the Black-Scholes Option Pricing Model to Determine the Fair Value of the Employee Stock Option Grants (Detail)	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions and Methodology [Abstract]
Risk-free interest rate	1.60%	1.01%
Expected volatility	65.80%	87.90%
Expected term (in years)	6 years 1 month 2 days	5 years 4 months 10 days
Expected dividend yield	0.00%	0.00%

Stock-Based Compensation - Summary of Weighted-Average Assumptions Used in the Black-Scholes Option Pricing Model to Determine the Fair Value of the Non-Employee Stock Option Grants (Detail)	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Share-based Goods and Nonemployee Services Transaction [Abstract]
Risk-free interest rate	0.56%	0.57%
Expected volatility	59.70%	109.90%
Expected term (in years)	2 years 2 months 19 days	2 years 1 month 17 days
Expected dividend yield	0.00%	0.00%

Income Taxes - Additional Information (Detail) - USD ($) $ in Thousands	Mar. 31, 2015	Dec. 31, 2014
Income Tax Disclosure [Abstract]
Noncurrent deferred tax assets, net	$ 1,034	$ 651
Current deferred tax liability, net	$ 1,034	$ 651