Dimension Therapeutics (DMTX) 10-Q 12 May 16 2016 Q1 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	3 Months Ended
	Mar. 31, 2016	May. 05, 2016
Document And Entity Information [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Mar. 31, 2016
Document Fiscal Year Focus	2,016
Document Fiscal Period Focus	Q1
Trading Symbol	DMTX
Entity Registrant Name	Dimension Therapeutics, Inc.
Entity Central Index Key	1,592,288
Current Fiscal Year End Date	--12-31
Entity Filer Category	Non-accelerated Filer
Entity Common Stock, Shares Outstanding		25,022,918

Condensed Consolidated Balance

Condensed Consolidated Balance Sheets (Unaudited) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Current assets:
Cash and cash equivalents	$ 117,027	$ 127,047
Accounts receivable	1,264	143
Prepaid expenses and other current assets	2,644	2,740
Total current assets	120,935	129,930
Property and equipment, net	6,245	3,339
Total assets	127,180	133,269
Current liabilities:
Accounts payable	2,238	1,555
Accrued expenses and other current liabilities	5,024	3,715
Amounts due to related parties		522
Deferred revenue	7,114	6,835
Notes payable	574	574
Total current liabilities	14,950	13,201
Deferred revenue, net of current portion	14,465	13,670
Notes payable, net of discount and current portion	616	759
Other liabilities	538	56
Total liabilities	$ 30,569	$ 27,686
Commitments and contingencies (Note 10)
Stockholders’ equity:
Preferred stock, $0.0001 par value; 5,000,000 shares authorized at March 31, 2016 and December 31, 2015; zero shares issued or outstanding at March 31, 2016 and December 31, 2015.	$ 0	$ 0
Common stock, $0.0001 par value; 150,000,000 shares authorized as of March 31, 2016 and December 31, 2015; 25,020,727 and 25,008,227 shares issued and outstanding as of March 31, 2016 and December 31, 2015, respectively.	2	2
Additional paid-in capital	157,315	156,775
Accumulated deficit	(60,706)	(51,194)
Total stockholders’ equity	96,611	105,583
Total liabilities and stockholders’ equity	$ 127,180	$ 133,269

Condensed Consolidated Balance3

Condensed Consolidated Balance Sheets (Unaudited) (Parenthetical) - $ / shares	Mar. 31, 2016	Dec. 31, 2015
Statement Of Financial Position [Abstract]
Preferred stock, par value	$ 0.0001	$ 0.0001
Preferred stock, shares authorized	5,000,000	5,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value	$ 0.0001	$ 0.0001
Common stock, shares authorized	150,000,000	150,000,000
Common stock, shares issued	25,020,727	25,008,227
Common stock, shares outstanding	25,020,727	25,008,227

Condensed Consolidated Statemen

Condensed Consolidated Statements of Operations and Comprehensive Loss (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Income Statement [Abstract]
Revenue	$ 2,206	$ 1,594
Operating expenses:
Research and development	8,805	5,506
General and administrative	2,941	1,453
Total operating expenses	11,746	6,959
Loss from operations	(9,540)	(5,365)
Interest income (expense), net	28	(24)
Net loss and comprehensive loss	(9,512)	(5,389)
Accretion of convertible preferred stock to redemption value		(19)
Net loss attributable to common stockholders	$ (9,512)	$ (5,408)
Net loss per share attributable to common stockholders — basic and diluted	$ (0.38)	$ (1.40)
Weighted average common shares outstanding — basic and diluted	24,851,933	3,853,262

Condensed Consolidated Stateme5

Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Cash flows from operating activities:
Net loss	$ (9,512)	$ (5,389)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization expense	216	128
Stock-based compensation expense	533	77
Non-cash interest expense	2	2
Changes in operating assets and liabilities:
Accounts receivable	(1,121)	(1,798)
Prepaid expenses and other current assets	96	(977)
Accounts payable	424	(791)
Accrued expenses and other current liabilities and amounts due to related parties	(1,040)	150
Deferred revenue	1,074	203
Other liabilities	(10)	81
Net cash (used in) provided by operating activities	(9,338)	(8,314)
Cash flows from investing activities:
Purchases of property and equipment	(544)	(817)
Net cash used in investing activities	(544)	(817)
Cash flows from financing activities:
Proceeds from issuance of convertible preferred stock, net of issuance costs		14,480
Proceeds from exercise of common stock options	7
Proceeds from issuance of notes payable and common stock warrant, net of issuance costs		194
Repayment of notes payable	(145)
Net cash provided by financing activities	(138)	14,674
Net increase in cash and cash equivalents	(10,020)	5,543
Cash and cash equivalents at beginning of period	127,047	17,913
Cash and cash equivalents at end of period	117,027	23,456
Supplemental disclosure of cash flow information:
Interest paid	26	22
Supplemental disclosure of non-cash investing and financing activities:
Accretion of convertible preferred stock to redemption value		19
Purchases of property and equipment included in accounts payable, accrued expenses and other liabilities	$ 2,578	$ 379

Nature of the Business and Basi

Nature of the Business and Basis of Presentation	3 Months Ended
	Mar. 31, 2016
Accounting Policies [Abstract]
Nature of the Business and Basis of Presentation	1. Nature of the Business and Basis of Presentation Dimension Therapeutics, Inc. (the “Company”) was incorporated in Delaware on June 20, 2013. The Company is a leader in discovering and developing new therapeutic products for people living with devastating rare diseases associated with the liver, based on the most advanced, mammalian adeno-associated virus (AAV) gene delivery technology. The liver is a vital organ that plays an important role in human metabolism and key physiologic functions, and is the target organ for our initial programs: OTC deficiency, GSDIa, hemophilia B, and hemophilia A. The Company is subject to risks and uncertainties common to early-stage companies in the biotechnology industry, including, but not limited to, development by competitors of new technological innovations, dependence on key personnel, protection of proprietary technology, compliance with government regulations and ability to secure additional capital to fund operations. Product candidates currently under development will require significant additional research and development efforts, including extensive preclinical and clinical testing and regulatory approval prior to commercialization. These efforts require significant amounts of additional capital, adequate personnel and infrastructure and extensive compliance-reporting capabilities. Even if the Company’s product development efforts are successful, it is uncertain when, if ever, the Company will realize significant revenue from product sales. The Company may not be able to obtain financing on acceptable terms, or at all, and the Company may not be able to enter into additional collaboration arrangements or obtain government grants. If the Company is unable to obtain funding, the Company could be forced to delay, reduce or eliminate its research and development programs, product portfolio expansion or commercialization efforts, which could adversely affect its business prospects. Although management continues to pursue these plans, there is no assurance that the Company will be successful in obtaining sufficient funding on terms acceptable to the Company to fund continuing operations, if at all. As of March 31, 2016, the Company had an accumulated deficit of $60,706. The Company expects to continue to generate operating losses in the foreseeable future. From our inception through March 31, 2016, we had received net proceeds of $88,895 from our sales of preferred stock, $64,620 from our IPO, $33,021 under the collaboration agreement with Bayer, and $1,750 from borrowings under a loan and security agreement.

Summary of Significant Accounti

Summary of Significant Accounting Policies	3 Months Ended
	Mar. 31, 2016
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	2. Summary of Significant Accounting Policies Basis of Presentation and Principles of Consolidation The accompanying condensed consolidated financial statements reflect the operations of Dimension Therapeutics, Inc. and Dimension Securities Corporation, our wholly-owned subsidiary. All intercompany accounts and transactions have been eliminated. The condensed consolidated financial statements are unaudited and have been prepared in accordance with accounting principles generally accepted in the United States of America (“GAAP”). The accounting policies followed in the preparation of the interim condensed consolidated financial statements are consistent in all material respects with those presented in Note 2 to the financial statements included on the Annual Report on Form 10-K for the fiscal year ended on December 31, 2015. Unaudited Interim Financial Information The condensed consolidated balance sheet at December 31, 2015 was derived from audited financial statements, but does not include all disclosures required by GAAP. The accompanying condensed consolidated balance sheet as of March 31, 2016, the condensed consolidated statements of operations and comprehensive loss for the three months ended March 31, 2016 and 2015 and of condensed consolidated cash flows for the three months ended March 31, 2016 and 2015 are unaudited. The unaudited interim condensed consolidated financial statements have been prepared on the same basis as the audited annual financial statements and, in the opinion of management, reflect all adjustments, which include only normal recurring adjustments, necessary for the fair statement of the Company’s financial position as of March 31, 2016 and the results of its operations and its cash flows for the three months ended March 31, 2016 and 2015. The financial data and other information disclosed in the notes related to the three months ended March 31, 2016 and 2015 are unaudited. The results for the three months ended March 31, 2016 are not necessarily indicative of results to be expected for the year ending December 31, 2016, any other interim periods, or any future year or period. The unaudited interim financial statements of the Company included herein have been prepared pursuant to the rules and regulations of the SEC. Certain information and footnote disclosures normally included in financial statements prepared in accordance with GAAP have been condensed or omitted from this report, as is permitted by such rules and regulations. These unaudited condensed consolidated financial statements should be read in conjunction with the audited financial statements and the notes thereto for the year ended December 31, 2015 included in the Company’s Annual Report on Form 10-K for the fiscal year ended December 31, 2015. Use of Estimates The preparation of financial statements in conformity with GAAP requires management to make estimates, assumptions and judgments that affect the reported amounts of assets and liabilities, the disclosure of contingent assets and liabilities at the date of the condensed consolidated financial statements, and the reported amounts of revenue and expenses during the reporting periods. Significant estimates, assumptions and judgments reflected in these condensed consolidated financial statements include, but are not limited to, the accrual of research and development expenses, the recognition of revenue from the Company’s collaboration with Bayer, the valuation of common stock prior to the IPO and the valuation of stock-based awards. Estimates are periodically reviewed in light of changes in circumstances, facts and experience. Actual results could differ from the Company’s estimates. Recently Issued Accounting Pronouncements In May 2014, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) 2014-09, Revenue from Contracts with Customers (Topic 606) Revenue from Contracts with Customers (Topic 606): Deferral of the Effective Date Revenue from Contracts with Customers (Topic 606): Principal versus Agent Considerations Revenue from Contracts with Customers (Topic 606): Identifying Performance Obligations and Licensing In August 2014, the FASB issued ASU 2014-15, Disclosure of Uncertainties about an Entity’s Ability to Continue as a Going Concern In February 2016, the FASB issued ASU 2016-02, Leases (Topic 842) In March 2016, the FASB issued ASU 2016-09, Compensation—Stock Compensation (Topic 718): Improvements to Employee Share-Based Payment Accounting

Fair Value of Financial Assets

Fair Value of Financial Assets	3 Months Ended
	Mar. 31, 2016
Fair Value Disclosures [Abstract]
Fair Value of Financial Assets	3. Fair Value of Financial Assets The following tables present information about the Company’s financial assets measured at fair value on a recurring basis and indicate the level of the fair value hierarchy utilized to determine such fair values: Fair Value Measurements as of March 31, 2016 using: Level 1 Level 2 Level 3 Total Assets: Cash equivalents $ 117,027 $ — $ — $ 117,027 $ 117,027 $ — $ — $ 117,027 Fair Value Measurements as of December 31, 2015 using: Level 1 Level 2 Level 3 Total Assets: Cash equivalents $ 127,047 $ — $ — $ 127,047 $ 127,047 $ — $ — $ 127,047 As of March 31, 2016 and December 31, 2015, the Company’s cash equivalents, which were invested in a money market fund, were valued based on Level 1 inputs. During the three months ended March 31, 2016 and the year ended December 31, 2015, there were no transfers between Level 1, Level 2 and Level 3.

Accrued Expenses and Other Curr

Accrued Expenses and Other Current Liabilities	3 Months Ended
	Mar. 31, 2016
Payables And Accruals [Abstract]
Accrued Expenses and Other Current Liabilities	4. Accrued Expenses and Other Current Liabilities Accrued expenses and other current liabilities consisted of the following: March 31, December 31, 2016 2015 Payroll and payroll-related costs $ 681 $ 2,000 External research and development services 1,987 1,389 Professional fees 452 254 Capital equipment 489 — Leasehold improvements 1,215 — Other 200 72 $ 5,024 $ 3,715

Notes Payable

Notes Payable	3 Months Ended
	Mar. 31, 2016
Debt Disclosure [Abstract]
Notes Payable	5. Notes Payable In February 2016, the Company entered into a Second Amendment to the loan and security agreement (the “Second Amendment”) with Silicon Valley Bank (SVB). Under the Second Amendment, the Company may borrow an aggregate principal amount of up to $7,000 for certain equipment purchases. In accordance with terms of the Second Amendment, the Company is obligated to make six monthly interest-only payments. Thereafter, the Company is obligated to pay thirty-six (36) monthly installments of interest and principal. Advances under the second amendment to loan and security agreement accrue interest at an annual rate of 0.5% below the Prime Rate, which interest shall be determined by SVB on the Funding Date of the applicable Equipment Advance and shall be payable monthly in arrears. In addition, upon the final monthly payment of each advance, the Company is required to make an additional payment equal to 6% of each advance original principal amount. Except as specifically amended by the Second Amendment, the Loan Agreement remains in full force and effect. Accretion of debt discount is recorded as additional interest expense and was $2 and $2 for the three months ended March 31, 2016 and 2015, respectively. As of March 31, 2016, the unamortized debt discount was $21. Estimated future principal payments due under the loan and security agreement with SVB as of March 31, 2016 are as follows: 2016 (remainder of year) $ 438 2017 583 2018 190 Total $ 1,211

Collaboration Agreement

Collaboration Agreement	3 Months Ended
	Mar. 31, 2016
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Collaboration Agreement	6. Collaboration Agreement Bayer HealthCare LLC In June 2014, the Company entered into a research and development collaboration and license agreement with Bayer for the development and commercialization of a gene therapy for the treatment of hemophilia A (the “collaboration agreement”). Under the agreement, the Company granted to Bayer an exclusive license to develop and commercialize one or more novel gene therapies for hemophilia A and a right of first notice for gene therapy treatments for hemophilia B. The Company is responsible for all research and development activities for those biologic therapeutics under the agreement prior to completion of clinical proof-of-concept (“POC”) trials, with Bayer funding the Company’s efforts and providing consulting and technological support. Upon the successful demonstration of clinical POC, the agreement requires that Bayer use commercially reasonable efforts to conduct later-stage development and commercialization of gene therapy products for treatment of hemophilia A for such therapy. Bayer will have worldwide rights to commercialize the potential future product. Financial Terms Under the terms of the agreement with Bayer, the Company received a nonrefundable, noncreditable upfront license payment of $20,000 in June 2014 and is eligible to receive development and commercialization milestone payments of up to $232,000, as well as tiered royalty payments ranging in the high single-digit to low double-digit percentages, not exceeding the mid-teens, of net sales of commercialized products resulting from the collaboration, as defined in the agreement with Bayer. Bayer will fund certain research and development services performed by the Company during the research term and will reimburse the Company for all project costs, including any third-party costs, in the performance of its obligations under the annual research plan and in accordance with the mutually agreed upon research budget. The Company determined that the deliverables under its agreement with Bayer include (i) research services to be provided over the research term, (ii) a development and commercialization license and (iii) the Company’s participation in a Joint Steering Committee (“JSC”) and a Joint Research and Development Committee (“JRDC”) to be provided over the research term. The Company determined that the development and commercialization license and involvement in the JSC and the JRDC do not have standalone value to Bayer and, therefore, are not separable from the delivery of the research services. Therefore, all deliverables under the agreement have been combined and accounted for as a single unit of accounting. Accordingly, the upfront license payment and research payments are being recognized by the Company as revenue on a straight-line basis over the estimated performance period, which approximates the 54-month research term of the agreement with Bayer that commenced in June 2014. As future research payments are earned, the Company will recognize as revenue the portion of payments equal to the percentage of the elapsed research term to the total estimated research term, with the remaining portion of consideration received being recognized over the remaining estimated performance period on a straight-line basis. The Company concluded at the outset of the arrangement that none of the future milestone payments included in the arrangement qualified as substantive milestones. Any future milestone payments will be recognized, along with the other arrangement consideration, over the remaining estimated period of performance, if any, beginning at the time a milestone payment is earned, with a cumulative catch-up being recognized for the elapsed portion of the estimated research term. As of March 31, 2016, the Company had not earned any milestone or royalty payments. Revenue recognized under the collaboration agreement with Bayer consisted of the following: Three Months Ended March 31, 2016 2015 Revenue: Bayer Collaboration $ 2,206 $ 1,594 $ 2,206 $ 1,594 During the three months ended March 31, 2016 and 2015, research payments earned by the Company under the collaboration agreement totaled $1,264 and $1,797, respectively. The costs incurred by the Company related to the research activities of the collaboration agreement are recorded as research and development expense in the condensed consolidated statement of operations and comprehensive loss. As of March 31, 2016 and December 31, 2015, deferred revenue related to the collaboration agreement with Bayer totaled $21,579 and $20,505, respectively, which related to the upfront license payment, research services payments and to advance payments for future research services. Term and Termination The agreement with Bayer expires on a licensed treatment-by-licensed treatment and country-by-country basis until the later of ten years from the date of first commercial sale or when patent claims have expired, lapsed, been abandoned or been invalidated in such country. The Company and Bayer, through the JSC, may mutually agree to terminate the collaboration early in the event clinical development is ended as required by a regulatory authority or in light of data from any studies conducted prior the POC trial. Bayer has the unilateral right to terminate the agreement in its entirety or with respect to one or more country by providing written notice to the Company. Bayer may also terminate the agreement with notice after two unsuccessful attempts to demonstrate clinical POC in a Phase I human POC trial. Bayer may further terminate the agreement with notice in the event that, following the POC trial, there is a material safety issue with respect to a licensed product. Reciprocal termination rights under the agreement include termination for breach and termination for bankruptcy.

Related Party Transactions

Related Party Transactions	3 Months Ended
	Mar. 31, 2016
Related Party Transactions [Abstract]
Related Party Transactions	7. Related Party Transactions As of January 1, 2016, the Company no longer considers the University of Pennsylvania (Penn) or REGENX to be related parties, as Penn and REGENX were no longer principal shareholders and REGENX was no longer represented on the Company’s board of directors. Accordingly, expenses incurred in connection with Penn or REGENX subsequent to January 1, 2016 are no longer considered to be related party expenses. Research and development expenses for Penn were $1,420 for the three months ended March 31, 2015. Cash payments made to the Penn during the three months ended March 31, 2015 were $2,137. Amounts due to Penn by the Company were $522 as of December 31, 2015.

Stock-Based Compensation

Stock-Based Compensation	3 Months Ended
	Mar. 31, 2016
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Stock-Based Compensation	8. Stock-Based Compensation 2015 Stock Option and Incentive Plan In September 2015, the Company’s stockholders approved the 2015 Stock Option and Incentive Plan (the “2015 Plan”). The 2015 Plan provides for the grant of incentive stock options, nonqualified stock options, stock appreciation rights, restricted stock units, restricted stock awards, performance share awards, cash-based awards and other stock-based awards. The 2015 Stock Option Plan replaced the Company’s 2013 Stock Option and Grant Plan (the “2013 Plan”). The Company will grant no future stock options or other awards under the 2013 Stock Option Plan. Any options or awards outstanding under the 2013 Stock Option Plan remained outstanding and effective. As of March 31, 2016, the total number of shares reserved under the 2015 Plan and the 2013 Stock Option Plan was 5,889,101 and the Company had 1,589,136 shares available for future issuance under the 2015 Stock Option Plan. The 2015 Plan provides for an annual increase, to be added on the first day of each fiscal year, by up to 4% of the Company’s issued and outstanding shares of common stock on the immediately preceding December 31. On January 1, 2016, 1,000,329 shares of common stock, representing 4% of the Company’s issued and outstanding shares of common stock as of December 31, 2015, were added to the 2015 Plan. Such shares are included in the equity plan totals specified in the paragraph above. During the three months ended March 31, 2016, the Company did not grant to non-employees any stock-based awards. Stock Option Valuation The fair value of each option granted to employees and directors during the three months ended March 31, 2016 and 2015 under the Company’s stock option plans has been calculated on the date of grant using the following assumptions: Three Months Ended March 31, 2016 2015 Expected dividend yield — — Expected volatility 83 - 87% — Risk free interest rate 1.5 - 1.6% — Expected term 6.0 years — During the three months ended March 31, 2015, the Company did not grant to employees and directors any stock option grants. For options granted to nonemployees, the expected life of the option used is ten years, which is the contractual term of each such option. All other assumptions used to calculate the grant date fair value are generally consistent with the assumptions used for options granted to employees. Stock Options The following table summarizes the Company’s stock option activity since December 31, 2015: Number of Shares Weighted Average Exercise Price Weighted Average Remaining Contractual Term Aggregate Intrinsic Value (in years) Outstanding as of December 31, 2015 3,097,022 $ 3.11 9.2 $ 25,618 Granted 761,900 $ 7.14 Exercised (12,500 ) $ 0.56 Cancelled or forfeited (3,519 ) $ 2.49 Outstanding as of March 31, 2016 3,842,903 $ 3.92 9.1 $ 15,636 Options vested and expected to vest as of March 31, 2016 3,842,903 $ 3.92 9.1 Options exercisable as of March 31, 2016 758,402 $ 2.07 8.7 $ 4,369 The aggregate intrinsic value of stock options is calculated as the difference between the exercise price of the stock options and the fair value of the Company’s common stock for those stock options that had exercise prices lower than the fair value of the Company’s common stock at March 31, 2016. The weighted average grant-date fair value of stock options granted during the three months ended March 31, 2016 was $7.14. Restricted Common Stock The Company has granted restricted common stock with time-based vesting conditions. Unvested shares of restricted common stock may not be sold or transferred by the holder. These restrictions lapse according to the time-based vesting conditions of each award. The following table summarizes the Company’s restricted common stock activity: Number of Shares Weighted Average Grant Date Fair Value Unvested restricted common stock at December 31, 2015 153,217 $ 0.87 Issued - $ - Vested (20,789 ) $ 0.85 Forfeited - $ - Unvested restricted common stock at March 31, 2016 132,428 $ 0.87 The total fair value of restricted common stock vested during the three months ended March 31, 2016 was $163. Stock-Based Compensation Stock-based compensation expense related to stock options and restricted common stock was classified in the condensed consolidated statements of operations and comprehensive loss as follows: Three Months Ended March 31, 2016 2015 Research and development $ 217 $ 61 General and administrative 316 16 $ 533 $ 77 As of March 31, 2016, total unrecognized compensation cost related to the unvested awards was $8,779, which is expected to be recognized over a weighted average period of 3.3 years.

Net Loss per Share

Net Loss per Share	3 Months Ended
	Mar. 31, 2016
Earnings Per Share [Abstract]
Net Loss per Share	9. Net Loss per Share Basic and diluted net loss per share attributable to common stockholders was calculated as follows: Three Months Ended March 31, 2016 2015 Numerator: Net loss $ (9,512 ) $ (5,389 ) Accretion of convertible preferred stock to redemption value — (19 ) Net loss attributable to common stockholders $ (9,512 ) $ (5,408 ) Denominator: Weighted average common shares outstanding — basic and diluted 24,996,921 4,056,818 Less: Weighted average shares of unvested restricted common stock outstanding (144,988 ) (203,556 ) Weighted average common shares outstanding used in calculating net loss per share attributable to common stockholders — basic and diluted 24,851,933 3,853,262 Net loss per share attributable to common stockholders — basic and diluted $ (0.38 ) $ (1.40 ) The Company’s potential dilutive securities, which include convertible preferred stock, stock options, unvested restricted common stock and a warrant to purchase common stock, have been excluded from the computation of diluted net loss per share as the effect would be to reduce the net loss per share. Therefore, the weighted average number of common shares outstanding used to calculate both basic and diluted net loss per share attributable to common stockholders are the same. The Company excluded the following potential common shares, presented based on amounts outstanding at each period end, from the computation of diluted net loss per share attributable to common stockholders for the periods indicated because including them would have had an antidilutive effect: Three Months Ended March 31, 2016 2015 Convertible preferred stock (as converted to common stock) — 8,381,798 Options to purchase common stock 3,842,903 1,104,185 Unvested restricted common stock 132,428 191,733 Warrant for the purchase of common stock — 11,973 3,975,331 9,689,689

Commitments and Contingencies

Commitments and Contingencies	3 Months Ended
	Mar. 31, 2016
Commitments And Contingencies Disclosure [Abstract]
Commitments and Contingencies	10. Commitments and Contingencies Leases The Company leases office and laboratory space under various operating lease agreements for its Cambridge, MA location that, as amended, expire between March 2015 and January 2018. The company recorded rent expense of $171 and $221 during the three months ended March 31, 2016 and 2015, respectively. The MA location that expires March 2021 The following table summarizes the future minimum lease payments under the Cambridge and Woburn operating leases as of March 31, 2016: Year Ending December 31, 2016 (remainder of year) $ 880 2017 1,205 2018 549 2019 506 2020 523 2021 132 Total $ 3,795 The Company is further responsible for its pro rata share of operating expenses, real estate taxes and utilities of the facilities housing the leased office and laboratory space. Legal Proceedings The Company is not currently party to any material legal proceedings. At each reporting date, the Company evaluates whether or not a potential loss amount or a potential range of loss is probable and reasonably estimable under the provisions of the authoritative guidance that addresses accounting for contingencies. The Company expenses as incurred the costs related to its legal proceedings. Indemnification Agreements In the ordinary course of business, the Company may provide indemnification of varying scope and terms to vendors, lessors, business partners and other parties with respect to certain matters including, but not limited to, losses arising out of breach of such agreements or from intellectual property infringement claims made by third parties. In addition, the Company has entered into indemnification agreements with members of its board of directors and certain executive officers that will require the Company, among other things, to indemnify them against certain liabilities that may arise by reason of their status or service as directors or officers. The maximum potential amount of future payments the Company could be required to make under these indemnification agreements is, in many cases, unlimited. To date, the Company has not incurred any material costs as a result of such indemnifications. The Company is not aware of any claims under indemnification arrangements, and it has not accrued any liabilities related to such obligations in its condensed consolidated financial statements as of March 31, 2016.

Subsequent Events

Subsequent Events	3 Months Ended
	Mar. 31, 2016
Subsequent Events [Abstract]
Subsequent Events	11. Subsequent Events In May 2016, the Company entered into a Research, Collaboration & License Agreement (the “Collaboration Agreement”) with The Trustees of the University of Pennsylvania (Penn). The Collaboration Agreement provides the terms for the Company and Penn to collaborate with respect to the pre-clinical development of gene therapy products for the treatment of Phenylketonuria (DTX501), Citrullinemia Type I (DTX601) and Wilson Disease (DTX701) (each, a “Subfield”). Under the Collaboration Agreement, Penn granted the Company an exclusive, worldwide, royalty-bearing right and license to certain patent rights arising out of the research program, subject to certain retained rights, and a non-exclusive, worldwide, royalty-bearing right and license to certain background patent rights, certain know-how, and certain materials, in each case to research, develop, make, have made, use, sell, offer for sale, commercialize and import licensed products in each Subfield for the term of the Collaboration Agreement. The Company will fund the cost of the research in accordance with a mutually agreed-upon research budget and will be responsible for clinical development and commercialization of the licensed products. On the effective date of the Collaboration Agreement, the Company paid to Penn a one-time, non-refundable issue fee and research payment, both of which were immaterial. As additional consideration for the licenses granted under the Collaboration Agreement, the Company will pay Penn milestone payments upon achievement of certain developmental and commercial milestones, of which near term milestones are expected to be immaterial, as well as low to mid single-digit royalties percentages on net sales of licensed products.

Summary of Significant Accoun17

Summary of Significant Accounting Policies (Policies)	3 Months Ended
	Mar. 31, 2016
Accounting Policies [Abstract]
Basis of Presentation and Principles of Consolidation	Basis of Presentation and Principles of Consolidation The accompanying condensed consolidated financial statements reflect the operations of Dimension Therapeutics, Inc. and Dimension Securities Corporation, our wholly-owned subsidiary. All intercompany accounts and transactions have been eliminated. The condensed consolidated financial statements are unaudited and have been prepared in accordance with accounting principles generally accepted in the United States of America (“GAAP”). The accounting policies followed in the preparation of the interim condensed consolidated financial statements are consistent in all material respects with those presented in Note 2 to the financial statements included on the Annual Report on Form 10-K for the fiscal year ended on December 31, 2015.
Unaudited Interim Financial Information	Unaudited Interim Financial Information The condensed consolidated balance sheet at December 31, 2015 was derived from audited financial statements, but does not include all disclosures required by GAAP. The accompanying condensed consolidated balance sheet as of March 31, 2016, the condensed consolidated statements of operations and comprehensive loss for the three months ended March 31, 2016 and 2015 and of condensed consolidated cash flows for the three months ended March 31, 2016 and 2015 are unaudited. The unaudited interim condensed consolidated financial statements have been prepared on the same basis as the audited annual financial statements and, in the opinion of management, reflect all adjustments, which include only normal recurring adjustments, necessary for the fair statement of the Company’s financial position as of March 31, 2016 and the results of its operations and its cash flows for the three months ended March 31, 2016 and 2015. The financial data and other information disclosed in the notes related to the three months ended March 31, 2016 and 2015 are unaudited. The results for the three months ended March 31, 2016 are not necessarily indicative of results to be expected for the year ending December 31, 2016, any other interim periods, or any future year or period. The unaudited interim financial statements of the Company included herein have been prepared pursuant to the rules and regulations of the SEC. Certain information and footnote disclosures normally included in financial statements prepared in accordance with GAAP have been condensed or omitted from this report, as is permitted by such rules and regulations. These unaudited condensed consolidated financial statements should be read in conjunction with the audited financial statements and the notes thereto for the year ended December 31, 2015 included in the Company’s Annual Report on Form 10-K for the fiscal year ended December 31, 2015.
Use of Estimates	Use of Estimates The preparation of financial statements in conformity with GAAP requires management to make estimates, assumptions and judgments that affect the reported amounts of assets and liabilities, the disclosure of contingent assets and liabilities at the date of the condensed consolidated financial statements, and the reported amounts of revenue and expenses during the reporting periods. Significant estimates, assumptions and judgments reflected in these condensed consolidated financial statements include, but are not limited to, the accrual of research and development expenses, the recognition of revenue from the Company’s collaboration with Bayer, the valuation of common stock prior to the IPO and the valuation of stock-based awards. Estimates are periodically reviewed in light of changes in circumstances, facts and experience. Actual results could differ from the Company’s estimates.
Recently Issued Accounting Pronouncements	Recently Issued Accounting Pronouncements In May 2014, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) 2014-09, Revenue from Contracts with Customers (Topic 606) Revenue from Contracts with Customers (Topic 606): Deferral of the Effective Date Revenue from Contracts with Customers (Topic 606): Principal versus Agent Considerations Revenue from Contracts with Customers (Topic 606): Identifying Performance Obligations and Licensing In August 2014, the FASB issued ASU 2014-15, Disclosure of Uncertainties about an Entity’s Ability to Continue as a Going Concern In February 2016, the FASB issued ASU 2016-02, Leases (Topic 842) In March 2016, the FASB issued ASU 2016-09, Compensation—Stock Compensation (Topic 718): Improvements to Employee Share-Based Payment Accounting

Fair Value of Financial Assets

Fair Value of Financial Assets (Tables)	3 Months Ended
	Mar. 31, 2016
Fair Value Disclosures [Abstract]
Schedule of Assets and Liabilities Measured at Fair Value on Recurring Basis	The following tables present information about the Company’s financial assets measured at fair value on a recurring basis and indicate the level of the fair value hierarchy utilized to determine such fair values: Fair Value Measurements as of March 31, 2016 using: Level 1 Level 2 Level 3 Total Assets: Cash equivalents $ 117,027 $ — $ — $ 117,027 $ 117,027 $ — $ — $ 117,027 Fair Value Measurements as of December 31, 2015 using: Level 1 Level 2 Level 3 Total Assets: Cash equivalents $ 127,047 $ — $ — $ 127,047 $ 127,047 $ — $ — $ 127,047

Accrued Expenses and Other Cu19

Accrued Expenses and Other Current Liabilities (Tables)	3 Months Ended
	Mar. 31, 2016
Payables And Accruals [Abstract]
Schedule of Accrued Expenses and Other Current Liabilities	Accrued expenses and other current liabilities consisted of the following: March 31, December 31, 2016 2015 Payroll and payroll-related costs $ 681 $ 2,000 External research and development services 1,987 1,389 Professional fees 452 254 Capital equipment 489 — Leasehold improvements 1,215 — Other 200 72 $ 5,024 $ 3,715

Notes Payable (Tables)

Notes Payable (Tables)	3 Months Ended
	Mar. 31, 2016
Debt Disclosure [Abstract]
Estimated Future Principal Payments Due	Estimated future principal payments due under the loan and security agreement with SVB as of March 31, 2016 are as follows: 2016 (remainder of year) $ 438 2017 583 2018 190 Total $ 1,211

Collaboration Agreement (Tables

Collaboration Agreement (Tables)	3 Months Ended
	Mar. 31, 2016
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Schedule of Revenue from Collaboration Agreement	Revenue recognized under the collaboration agreement with Bayer consisted of the following: Three Months Ended March 31, 2016 2015 Revenue: Bayer Collaboration $ 2,206 $ 1,594 $ 2,206 $ 1,594

Stock-Based Compensation (Table

Stock-Based Compensation (Tables)	3 Months Ended
	Mar. 31, 2016
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Schedule of Assumptions Used in Fair Value of Options Granted to Employees and Directors Under Stock Option Plans	The fair value of each option granted to employees and directors during the three months ended March 31, 2016 and 2015 under the Company’s stock option plans has been calculated on the date of grant using the following assumptions: Three Months Ended March 31, 2016 2015 Expected dividend yield — — Expected volatility 83 - 87% — Risk free interest rate 1.5 - 1.6% — Expected term 6.0 years —
Summary of Stock Option Activity	The following table summarizes the Company’s stock option activity since December 31, 2015: Number of Shares Weighted Average Exercise Price Weighted Average Remaining Contractual Term Aggregate Intrinsic Value (in years) Outstanding as of December 31, 2015 3,097,022 $ 3.11 9.2 $ 25,618 Granted 761,900 $ 7.14 Exercised (12,500 ) $ 0.56 Cancelled or forfeited (3,519 ) $ 2.49 Outstanding as of March 31, 2016 3,842,903 $ 3.92 9.1 $ 15,636 Options vested and expected to vest as of March 31, 2016 3,842,903 $ 3.92 9.1 Options exercisable as of March 31, 2016 758,402 $ 2.07 8.7 $ 4,369
Summary of Restricted Common Stock Activity	The following table summarizes the Company’s restricted common stock activity: Number of Shares Weighted Average Grant Date Fair Value Unvested restricted common stock at December 31, 2015 153,217 $ 0.87 Issued - $ - Vested (20,789 ) $ 0.85 Forfeited - $ - Unvested restricted common stock at March 31, 2016 132,428 $ 0.87
Summary of Stock-Based Compensation Expense Related to Stock Options and Restricted Common Stock	Stock-based compensation expense related to stock options and restricted common stock was classified in the condensed consolidated statements of operations and comprehensive loss as follows: Three Months Ended March 31, 2016 2015 Research and development $ 217 $ 61 General and administrative 316 16 $ 533 $ 77

Net Loss per Share (Tables)

Net Loss per Share (Tables)	3 Months Ended
	Mar. 31, 2016
Earnings Per Share [Abstract]
Schedule of Basic and Diluted Net Loss per Share Attributable to Common Stockholders	Basic and diluted net loss per share attributable to common stockholders was calculated as follows: Three Months Ended March 31, 2016 2015 Numerator: Net loss $ (9,512 ) $ (5,389 ) Accretion of convertible preferred stock to redemption value — (19 ) Net loss attributable to common stockholders $ (9,512 ) $ (5,408 ) Denominator: Weighted average common shares outstanding — basic and diluted 24,996,921 4,056,818 Less: Weighted average shares of unvested restricted common stock outstanding (144,988 ) (203,556 ) Weighted average common shares outstanding used in calculating net loss per share attributable to common stockholders — basic and diluted 24,851,933 3,853,262 Net loss per share attributable to common stockholders — basic and diluted $ (0.38 ) $ (1.40 )
Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share	The Company excluded the following potential common shares, presented based on amounts outstanding at each period end, from the computation of diluted net loss per share attributable to common stockholders for the periods indicated because including them would have had an antidilutive effect: Three Months Ended March 31, 2016 2015 Convertible preferred stock (as converted to common stock) — 8,381,798 Options to purchase common stock 3,842,903 1,104,185 Unvested restricted common stock 132,428 191,733 Warrant for the purchase of common stock — 11,973 3,975,331 9,689,689

Commitments and Contingencies (

Commitments and Contingencies (Tables)	3 Months Ended
	Mar. 31, 2016
Commitments And Contingencies Disclosure [Abstract]
Schedule of Future Minimum Lease Payments under Operating Leases	The following table summarizes the future minimum lease payments under the Cambridge and Woburn operating leases as of March 31, 2016: Year Ending December 31, 2016 (remainder of year) $ 880 2017 1,205 2018 549 2019 506 2020 523 2021 132 Total $ 3,795

Nature of the Business and Ba25

Nature of the Business and Basis of Presentation - Additional Information (Detail) - USD ($) $ in Thousands	33 Months Ended
	Mar. 31, 2016	Dec. 31, 2015
Nature Of Business And Basis Of Presentation [Line Items]
Accumulated deficit	$ 60,706	$ 51,194
Net proceeds from sale of preferred stock	88,895
Net proceeds from initial public offering	64,620
Loan and Security Agreement [Member]
Nature Of Business And Basis Of Presentation [Line Items]
Net proceeds from borrowings	1,750
Collaboration Agreement [Member] | Bayer Healthcare LLC [Member]
Nature Of Business And Basis Of Presentation [Line Items]
Net proceeds from collaboration agreement	$ 33,021

Fair Value of Financial Asset26

Fair Value of Financial Assets - Schedule of Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Assets:
Cash equivalents	$ 117,027	$ 127,047
Assets total	117,027	127,047
Level 1 [Member] | Fair Value, Measurements, Recurring [Member]
Assets:
Cash equivalents	117,027	127,047
Assets total	$ 117,027	$ 127,047

Fair Value of Financial Asset27

Fair Value of Financial Assets - Additional Information (Detail) - USD ($)	3 Months Ended	12 Months Ended
	Mar. 31, 2016	Dec. 31, 2015
Debt Instrument Fair Value Carrying Value [Abstract]
Assets, Level 1 to Level 2 transfers, amount	$ 0	$ 0
Liabilities, Level 1 to Level 2 transfers, amount	0	0
Assets, Level 2 to Level 1 transfers, amount	0	0
Liabilities, Level 2 to Level 1 transfers, amount	0	0
Assets, transfers into Level 3, amount	0	0
Liabilities, transfers into Level 3, amount	0	0
Assets, transfers out of Level 3, amount	0	0
Liabilities, transfers out of Level 3, amount	$ 0	$ 0

Accrued Expenses and Other Cu28

Accrued Expenses and Other Current Liabilities - Accrued Expenses and Other Current Liabilities (Detail) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Payables And Accruals [Abstract]
Payroll and payroll-related costs	$ 681	$ 2,000
External research and development services	1,987	1,389
Professional fees	452	254
Capital equipment	489
Leasehold improvements	1,215
Other	200	72
Total	$ 5,024	$ 3,715

Notes Payable - Additional Info

Notes Payable - Additional Information (Detail) - USD ($)	Feb. 29, 2016	Mar. 31, 2016	Mar. 31, 2015
Second Amendment to Loan and Security Agreement [Member]
Line of Credit Facility [Line Items]
Maximum borrowings under line of credit	$ 7,000,000
Periodic payment term of interest		6 months
Periodic payment term of interest and principal		36 months
Accrue interest at annual rate below prime rate, to be determined on date of drawdown	0.50%
Percentage of interest accrue on additional final payment upon maturity or early termination	6.00%
Loan and Security Agreement [Member]
Line of Credit Facility [Line Items]
Accretion of debt discount		$ 2,000	$ 2,000
Unamortized debt discount		$ 21,000

Notes Payable - Estimated Futur

Notes Payable - Estimated Future Principal Payments Due (Detail) - Loan and Security Agreement [Member] $ in Thousands	Mar. 31, 2016USD ($)
Line of Credit Facility [Line Items]
2016 (remainder of year)	$ 438
2,017	583
2,018	190
Total	$ 1,211

Collaboration Agreement - Addit

Collaboration Agreement - Additional Information (Detail) - Bayer Healthcare LLC [Member] - Collaboration Agreement [Member] - USD ($)	1 Months Ended	3 Months Ended
	Jun. 30, 2014	Mar. 31, 2016	Mar. 31, 2015	Dec. 31, 2015
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Upfront license payment received	$ 20,000,000
Research agreement period	54 months
Research agreement commencement date	2014-06
Research payments earned		$ 1,264,000	$ 1,797,000
Deferred revenue		$ 21,579,000		$ 20,505,000
Maximum [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Potential future milestone payments receivable under development and commercialization activities	$ 232,000,000

Collaboration Agreement - Sched

Collaboration Agreement - Schedule of Revenue from Collaboration Agreement (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Revenue:
Revenue	$ 2,206	$ 1,594
Collaboration Agreement [Member] | Bayer Healthcare LLC [Member]
Revenue:
Revenue	$ 2,206	$ 1,594

Related Party Transactions - Ad

Related Party Transactions - Additional Information (Detail) - University of Pennsylvania [Member] - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2015	Dec. 31, 2015
Related Party Transaction [Line Items]
Related party expenses	$ 1,420
Cash payment to related party	$ 2,137
Amounts due to related party		$ 522

Stock-Based Compensation - Addi

Stock-Based Compensation - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2016	Mar. 31, 2015	Dec. 31, 2015	Sep. 30, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock options granted in connection with stock option plan	761,900
Weighted average grant-date fair value of stock options granted	$ 7.14
Total unrecognized compensation cost related to the unvested awards	$ 8,779
Unrecognized compensation cost related to the unvested awards, weighted-average period	3 years 3 months 18 days
Restricted Common Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total fair value of restricted common stock vested	$ 163
Non Employees [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term	10 years
Employees and Directors [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock options granted in connection with stock option plan		0
2015 and 2013 Stock Option Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock reserved for issuance	5,889,101
2013 Stock Option Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock reserved for future grant				0
2015 Stock Option Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock reserved for issuance	1,589,136
2015 Stock Option and Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock reserved for issuance, percentage of number of shares of common stock issued and outstanding			4.00%
Additional common stock reserved for issuance			1,000,329
2015 Stock Option and Incentive Plan [Member] | Non Employees [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock options granted in connection with employee stock purchase plan	0

Stock-Based Compensation - Sche

Stock-Based Compensation - Schedule of Assumptions Used in Fair Value of Options Granted to Employees and Directors Under Stock Option Plans (Detail)	3 Months Ended
	Mar. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected volatility, Minimum	83.00%
Expected volatility, Maximum	87.00%
Risk free interest rate, Minimum	1.50%
Risk free interest rate, Maximum	1.60%
Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term	6 years

Stock-Based Compensation - Summ

Stock-Based Compensation - Summary of Stock Option Activity (Detail) - USD ($)	3 Months Ended	12 Months Ended
	Mar. 31, 2016	Dec. 31, 2015
Sharebased Compensation Arrangement By Sharebased Payment Award Options Outstanding Weighted Average Exercise Price And Additional Disclosures [Abstract]
Outstanding, Number of Shares, Beginning Balance	3,097,022
Granted, Number of Shares	761,900
Exercised, Number of Shares	(12,500)
Cancelled or forfeited, Number of Shares	(3,519)
Outstanding, Number of Shares, Ending Balance	3,842,903	3,097,022
Options vested and expected to vest, Number of Shares	3,842,903
Options exercisable, Number of Shares	758,402
Outstanding, Weighted Average Exercise Price, Beginning Balance	$ 3.11
Granted, Weighted Average Exercise Price	7.14
Exercised, Weighted Average Exercise Price	0.56
Cancelled or forfeited, Weighted Average Exercise Price	2.49
Outstanding, Weighted Average Exercise Price, Ending Balance	3.92	$ 3.11
Options vested and expected to vest, Weighted Average Exercise Price	3.92
Options exercisable, Weighted Average Exercise Price	$ 2.07
Outstanding, Weighted Average Remaining Contractual Term	9 years 1 month 6 days	9 years 2 months 12 days
Options vested and expected to vest, Weighted Average Remaining Contractual Term	9 years 1 month 6 days
Options exercisable, Weighted Average Remaining Contractual Term	8 years 8 months 12 days
Outstanding, Aggregate Intrinsic Value	$ 15,636	$ 25,618
Options exercisable, Aggregate Intrinsic Value	$ 4,369

Stock-Based Compensation - Su37

Stock-Based Compensation - Summary of Restricted Common Stock Activity (Detail) - Restricted Common Stock [Member]	3 Months Ended
	Mar. 31, 2016$ / sharesshares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unvested restricted common stock, Number of Shares, Beginning Balance | shares	153,217
Vested, Number of Shares | shares	(20,789)
Unvested restricted common stock, Number of Shares, Ending Balance | shares	132,428
Unvested restricted common stock, Weighted Average Grant Date Fair Value, Beginning Balance | $ / shares	$ 0.87
Vested, Weighted Average Grant Date Fair Value | $ / shares	0.85
Unvested restricted common stock, Weighted Average Grant Date Fair Value, Ending Balance | $ / shares	$ 0.87

Stock-Based Compensation - Su38

Stock-Based Compensation - Summary of Stock-Based Compensation Expense Related to Stock Options and Restricted Common Stock (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	$ 533	$ 77
Research and Development [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	217	61
General and Administrative [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	$ 316	$ 16

Net Loss per Share - Schedule o

Net Loss per Share - Schedule of Basic and Diluted Net Loss per Share Attributable to Common Stockholders (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Numerator:
Net loss	$ (9,512)	$ (5,389)
Accretion of convertible preferred stock to redemption value		(19)
Net loss attributable to common stockholders	$ (9,512)	$ (5,408)
Denominator:
Weighted average common shares outstanding — basic and diluted	24,996,921	4,056,818
Less: Weighted average shares of unvested restricted common stock outstanding	(144,988)	(203,556)
Weighted average common shares outstanding used in calculating net loss per share attributable to common stockholders — basic and diluted	24,851,933	3,853,262
Net loss per share attributable to common stockholders — basic and diluted	$ (0.38)	$ (1.40)

Net Loss per Share - Schedule40

Net Loss per Share - Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share (Detail) - shares	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of diluted net loss per share	3,975,331	9,689,689
Convertible Preferred Stock (as Converted to Common Stock) [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of diluted net loss per share		8,381,798
Options to Purchase Common Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of diluted net loss per share	3,842,903	1,104,185
Restricted Common Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of diluted net loss per share	132,428	191,733
Warrant for the Purchase of Common Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of diluted net loss per share		11,973

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Detail) - Laboratory and Office Facility [Member] - USD ($)	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Cambridge, MA Location [Member]
Commitments and Contingencies [Line Items]
Operating lease expiration period start	2015-03
Operating lease expiration period end	2018-01
Operating leases, rent expense	$ 171,000	$ 221,000
Woburn, MA Location [Member]
Commitments and Contingencies [Line Items]
Operating leases, rent expense	$ 0
Lease expiration date	2021-03
Lease start date	Apr. 1, 2016

Commitments and Contingencies42

Commitments and Contingencies - Schedule of Future Minimum Lease Payments under Operating Leases (Detail) - Cambridge and Woburn Operating Leases [Member] $ in Thousands	Mar. 31, 2016USD ($)
Operating Leased Assets [Line Items]
2016 (remainder of year)	$ 880
2,017	1,205
2,018	549
2,019	506
2,020	523
2,021	132
Total	$ 3,795