Flexion Therapeutics (FLXN) 10-Q 7 Nov 16 2016 Q3 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	9 Months Ended
	Sep. 30, 2016	Oct. 31, 2016
Document And Entity Information [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Sep. 30, 2016
Document Fiscal Year Focus	2,016
Document Fiscal Period Focus	Q3
Trading Symbol	FLXN
Entity Registrant Name	Flexion Therapeutics Inc
Entity Central Index Key	1,419,600
Current Fiscal Year End Date	--12-31
Entity Filer Category	Accelerated Filer
Entity Common Stock, Shares Outstanding		27,527,419

Condensed Consolidated Balance

Condensed Consolidated Balance Sheets (Unaudited) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
Current assets:
Cash and cash equivalents	$ 66,809	$ 62,944
Marketable securities	92,693	48,303
Accounts receivable		95
Prepaid expenses and other current assets	1,584	761
Total current assets	161,086	112,103
Property and equipment, net	11,223	7,442
Long-term investments	2,003	7,357
Other assets	30	157
Restricted cash	80	80
Total assets	174,422	127,139
Current liabilities:
Accounts payable	2,029	3,692
Accrued expenses and other current liabilities	3,724	4,367
Current portion of long-term debt	6,634
Total current liabilities	12,387	8,059
Long-term debt	23,664	15,002
Other long-term liabilities	339	91
Total liabilities	36,390	23,152
Commitments and contingencies
Preferred Stock, $0.001 par value; 10,000,000 shares authorized at September 30, 2016 and December 31, 2015 and 0 shares issued and outstanding at September 30, 2016 and December 31, 2015
Stockholders’ equity:
Common stock, $0.001 par value; 100,000,000 shares authorized; 27,527,419 and 21,570,395 shares issued and outstanding, at September 30, 2016 and December 31, 2015, respectively	28	22
Additional paid-in capital	326,605	243,854
Accumulated other comprehensive income	(27)	(97)
Accumulated deficit	(188,574)	(139,792)
Total stockholders’ equity	138,032	103,987
Total liabilities and stockholders’ equity	$ 174,422	$ 127,139

Condensed Consolidated Balance3

Condensed Consolidated Balance Sheets (Unaudited) (Parenthetical) - $ / shares	Sep. 30, 2016	Dec. 31, 2015
Statement Of Financial Position [Abstract]
Preferred stock, par value	$ 0.001	$ 0.001
Preferred stock, shares authorized	10,000,000	10,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value	$ 0.001	$ 0.001
Common stock, shares authorized	100,000,000	100,000,000
Common stock, shares issued	27,527,419	21,570,395
Common stock, shares outstanding	27,527,419	21,570,395

Condensed Consolidated Statemen

Condensed Consolidated Statements of Operations and Comprehensive Loss (Unaudited) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Income Statement [Abstract]
Revenue	$ 0
Operating expenses:
Research and development	9,047	$ 7,829	$ 29,933	$ 23,724
General and administrative	8,388	3,197	18,295	8,860
Total operating expenses	17,435	11,026	48,228	32,584
Loss from operations	(17,435)	(11,026)	(48,228)	(32,584)
Other income (expense):
Interest income	421	274	1,052	882
Interest expense	(561)	(202)	(1,039)	(406)
Other income (expense), net	(207)	(182)	(567)	(639)
Total other income (expense)	(347)	(110)	(554)	(163)
Net loss	$ (17,782)	$ (11,136)	$ (48,782)	$ (32,747)
Net loss per share basic and diluted	$ (0.65)	$ (0.52)	$ (2.04)	$ (1.52)
Weighted average common shares outstanding, basic and diluted	27,524	21,507	23,938	21,478
Other comprehensive (loss) income:
Unrealized gains from available-for-sale securities, net of tax of $0	$ 38	$ 9	$ (70)	$ 8
Total other comprehensive (loss) income	38	9	(70)	8
Comprehensive loss	$ (17,744)	$ (11,127)	$ (48,852)	$ (32,739)

Condensed Consolidated Stateme5

Condensed Consolidated Statements of Operations and Comprehensive Loss (Unaudited) (Parenthetical) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Income Statement [Abstract]
Unrealized gains from available-for-sale securities, tax	$ 0	$ 0	$ 0	$ 0

Condensed Consolidated Stateme6

Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015
Cash flows from operating activities
Net loss	$ (48,782)	$ (32,747)
Adjustments to reconcile net loss to cash used in operating activities:
Depreciation	700	130
Stock-based compensation expense	4,963	3,099
Amortization of premium (discount) on marketable securities	544	637
Other non-cash charges	26	31
Loss on disposal of fixed assets	2,278
Premium paid on securities purchased	(273)
Changes in operating assets and liabilities:
Accounts receivable	95	(46)
Prepaid expenses, other current and long-term assets	(697)	(243)
Accounts payable	(1,029)	389
Accrued expenses and other current and long-term liabilities	690	786
Net cash used in operating activities	(41,485)	(27,964)
Cash flows from investing activities
Purchases of property and equipment	(8,165)	(2,415)
Change in restricted cash		24
Purchases of marketable securities	(80,151)	(106,465)
Sale and redemption of marketable securities	40,897	95,704
Discount received on securities purchased	17
Net cash used in investing activities	(47,402)	(13,152)
Cash flows from financing activities
Payment of debt issuance costs	(42)	(108)
Payments on debt		(3,500)
Proceeds from the offering of common stock, net of underwriter's commission and fees	77,644
Proceeds from the issuance of notes payable	15,000	15,004
Payments of public offering costs	(256)	(225)
Proceeds from the exercise of stock options	166	216
Proceeds from Employee Stock Purchase Plan	240	138
Net cash provided by financing activities	92,752	11,525
Net increase (decrease) in cash and cash equivalents	3,865	(29,591)
Cash and cash equivalents at beginning of period	62,944	103,098
Cash and cash equivalents at end of period	66,809	73,507
Supplemental disclosures of cash flow information:
Cash paid for interest	$ 823	370
Supplemental disclosures of non-cash financing activities:
Purchases of property and equipment in accounts payable and accrued expenses		$ 811

Overview and Nature of the Busi

Overview and Nature of the Business	9 Months Ended
	Sep. 30, 2016
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Overview and Nature of the Business	1. Overview and Nature of the Business Flexion Therapeutics, Inc. (“Flexion,” the “Company,” “we,” “our,” or “us”) was incorporated under the laws of the state of Delaware on November 5, 2007. Flexion is a specialty pharmaceutical company focused on the development and commercialization of novel, local therapies for the treatment of patients with musculoskeletal conditions, beginning with osteoarthritis (“OA”), a type of degenerative arthritis. The Company’s lead product candidate, Zilretta™ (also known as FX006), is a late-stage, injectable, extended-release, intra-articular, or IA, meaning “in the joint,” investigational steroid that is being developed as a treatment for patients with moderate to severe knee OA pain. The Company is subject to risks and uncertainties common to companies in the biopharmaceutical industry, including, but not limited to, new technological innovations, dependence on key personnel, protection of proprietary technology, compliance with government regulations, and the 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 infrastructure and extensive compliance reporting capabilities. The Company’s product candidates are all in the development stage. There can be no assurance that development efforts, including clinical trials, will be successful. 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.

Financing Activities

Financing Activities	9 Months Ended
	Sep. 30, 2016
Stockholders Equity Note [Abstract]
Financing Activities	2. Financing Activities On June 13, 2016, the Company completed a follow-on public offering of its common stock (the “2016 Offering”), which resulted in the sale of 5,500,000 shares of the Company’s common stock at a price to the public of $14.00 per share. On June 21, 2016, the Company completed the sale of an additional 400,000 shares of its common stock at the public offering price pursuant to the underwriters’ exercise of their option to purchase additional shares. The Company received aggregate gross proceeds from the 2016 Offering of $77.6 million after deducting underwriting commissions and fees paid by the Company. The Company’s total issued common stock as of September 30, 2016 was 27,527,419.

Summary of Significant Accounti

Summary of Significant Accounting Policies	9 Months Ended
	Sep. 30, 2016
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	3. Summary of Significant Accounting Policies Basis of Presentation The accompanying condensed consolidated financial statements as of September 30, 2016, and for the three and nine months ended September 30, 2016 and September 30, 2015, have been prepared in accordance with the rules and regulations of the Securities and Exchange Commission (the “SEC”) and Generally Accepted Accounting Principles (“GAAP”) for consolidated financial information including the accounts of the Company and its wholly-owned subsidiary after elimination of all significant intercompany accounts and transactions. Accordingly, they do not include all of the information and footnotes required by GAAP for complete financial statements. In the opinion of management, these condensed consolidated financial statements reflect all adjustments which are necessary for a fair statement of the Company’s financial position and results of its operations, as of and for the periods presented. These condensed consolidated financial statements should be read in conjunction with the consolidated financial statements and notes thereto contained in the Company’s Annual Report on Form 10-K filed with the SEC on March 11, 2016. The information presented in the condensed consolidated financial statements and related notes as of September 30, 2016, and for the three and nine months ended September 30, 2016 and September 30, 2015, is unaudited. The December 31, 2015 consolidated balance sheet included herein was derived from the audited financial statements as of that date, but does not include all disclosures, including notes, required by GAAP for complete financial statements. Interim results for the three and nine months ended September 30, 2016 are not necessarily indicative of the results that may be expected for the fiscal year ending December 31, 2016, or any future period. The accompanying condensed consolidated financial statements have been prepared on a basis which assumes that the Company will continue as a going concern and which contemplates the realization of assets and satisfaction of liabilities and commitments in the normal course of business. The Company has incurred recurring losses and negative cash flows from operations. As of September 30, 2016 and December 31, 2015, the Company had cash, cash equivalents, marketable securities, and long-term investments of $161,505,000 and $118,604,000, respectively. Management believes that current cash, cash equivalents and marketable securities on hand at September 30, 2016 should be sufficient to fund operations for at least the next twelve months. The future viability of the Company is dependent on its ability to raise additional capital to finance its operations, to fund increased research and development costs in order to seek approval for commercialization of its product candidates, and to successfully commercialize Zilretta, if approved. The Company’s failure to raise capital as and when needed would have a negative impact on its financial condition and its ability to pursue its business strategies as this capital is necessary for the Company to perform the research and development activities required to develop and seek approval for commercialization of the Company’s product candidates, to establish a commercial infrastructure in order to generate future revenue streams, and to successfully commercialize Zilretta, if approved. In August 2014, the FASB issued ASU No. 2014-15, Presentation of Financial Statements — Going Concern: Disclosure of Uncertainties about an Entity’s Ability to Continue as a Going Concern In April 2015, the FASB released Accounting Standards Update (“ASU”) 2015-05, Customers Accounting for Fees Paid in a Cloud Computing Arrangement . In November 2015, the FASB issued ASU 2015-17, Income Taxes In February 2016, the FASB issued ASU 2016-02, Leases In March 2016, the FASB released ASU 2016-09, which amends ASC Topic 718, Compensation-Stock Compensation, to require changes to several areas of employee share-based payment accounting in an effort to simplify share-based reporting. The update revises requirements in the following areas: minimum statutory withholding, accounting for income taxes, forfeitures, and intrinsic value accounting for private entities. For public companies, the new rules will become effective for annual reporting periods beginning after December 15, 2016, and interim reporting periods within such annual period. In August 2016, the FASB issued ASU 2016-15, Statement of cash flows Consolidation The accompanying condensed consolidated financial statements include the Company and its wholly-owned subsidiary, Flexion Securities Corporation, Inc. The Company has eliminated all intercompany transactions for the three and nine months ended September 30, 2016 and the year ended December 31, 2015, the year Flexion Securities Corporation, Inc. was established. U.S. Government Grant The Company previously performed research and development for the U.S. Department of Defense under a cost reimbursable grant for a Phase 2 clinical trial investigating Zilretta in active military and medically retired veterans with post-traumatic knee OA. Due to the challenges of enrolling military personnel with post-traumatic knee OA, the Company discontinued the trial and terminated the grant. The related costs incurred under the grant prior to the termination have been included in research and development expense in the statement of operations. The Company was reimbursed and has offset research and development expenses in the statement of operations when invoices for allowable costs were prepared and submitted to the U.S. Department of Defense. Payments under cost reimbursable grants with agencies of the U.S. government are provisional payments subject to adjustment upon audit by the U.S. government. Accounts Receivable Accounts receivable represents allowable costs under the Company’s now terminated U.S. Government agency grant for which the Company has not yet received reimbursement. The Company invoiced the government on a quarterly basis for reimbursable costs under the grant. Reimbursable costs that have not been invoiced on the last day of the quarter are recorded as unbilled accounts receivable. As of September 30, 2016 there were no unbilled accounts receivable, and as of December 31, 2015, there were unbilled accounts receivable of $95,000. Use of Estimates The preparation of financial statements in conformity with GAAP requires management to make estimates and judgments that may affect the reported amounts of assets and liabilities, expenses and related disclosures. The Company bases estimates and judgments on historical experience and on various other factors that it believes to be reasonable under the circumstances. The most significant estimates in these condensed consolidated financial statements include useful lives with respect to long-lived assets, such as property and equipment and leasehold improvements, accounting for stock-based compensation, and accrued expenses, including clinical research costs. The Company’s actual results may differ from these estimates under different assumptions or conditions. The Company evaluates its estimates on an ongoing basis. Changes in estimates are reflected in reported results in the period in which they become known by the Company’s management. Property and Equipment Property and equipment are stated at cost less accumulated depreciation. Depreciation and amortization expense is recognized using the straight-line method over the following estimated useful lives: Estimated Useful Life (Years) Computers, office equipment, and minor computer software 3 Computer software 7 Manufacturing equipment 7-10 Furniture and fixtures 5 Leasehold improvements are amortized over the shorter of the lease term or the estimated useful life of the related asset. Costs of major additions and improvements are capitalized and depreciated on a straight-line basis over their useful lives. Repairs and maintenance costs are expensed as incurred. Upon retirement or sale, the cost of assets disposed of and the related accumulated depreciation are removed from the accounts and any resulting gain or loss is credited or charged to income. Property and equipment includes construction-in-progress that is not yet in service. Foreign Currencies The Company maintains a bank account denominated in British Pounds. All foreign currency payables and cash balances are measured at the applicable exchange rate at the end of the reporting period. All associated gains and losses from foreign currency transactions are reflected in the consolidated statements of operations.

Fair Value of Financial Assets

Fair Value of Financial Assets and Liabilities	9 Months Ended
	Sep. 30, 2016
Fair Value Disclosures [Abstract]
Fair Value of Financial Assets and Liabilities	4. Fair Value of Financial Assets and Liabilities The following tables present information about the Company’s assets that are measured at fair value on a recurring basis as of September 30, 2016 and December 31, 2015 and indicate the level of the fair value hierarchy utilized to determine such fair value: Fair Value Measurements as of September 30, 2016 Using: (In thousands) Level 1 Level 2 Level 3 Total Assets: Cash equivalents $ — $ 44,540 $ — $ 44,540 Marketable securities — 94,696 — 94,696 $ — $ 139,236 $ — $ 139,236 Fair Value Measurements as of December 31, 2015 Using: (In thousands) Level 1 Level 2 Level 3 Total Assets: Cash equivalents $ — $ 61,534 $ — $ 61,534 Marketable securities — 55,660 — 55,660 $ — $ 117,194 $ — $ 117,194 As of September 30, 2016 and December 31, 2015, the Company’s cash equivalents that are invested in money market funds are valued based on Level 2 inputs. The Company measures the fair value of marketable securities, which consist of U.S. government obligations, commercial paper, and corporate bonds, using Level 2 inputs and primarily relies on quoted prices in active markets for similar marketable securities. During the nine months ended September 30, 2016 and year ended December 31, 2015, there were no transfers between Level 1, Level 2, and Level 3. The carrying values of accounts receivable, prepaid expenses, other current assets, accounts payable and accrued expenses approximate their fair value due to the short-term nature of these balances. The Company has a term loan outstanding under its 2015 credit facility with MidCap Financial Funding XIII Trust and Silicon Valley Bank (the “2015 term loan”). The amount outstanding on its 2015 term loan is reported at its carrying value in the accompanying balance sheet. The Company determined the fair value of the 2015 term loan using an income approach that utilizes a discounted cash flow analysis based on current market interest rates for debt issuances with similar remaining years to maturity, adjusted for credit risk. The 2015 term loan was valued using Level 2 inputs as of September 30, 2016 and December 31, 2015. The result of the calculation yielded a fair value that approximates its carrying value.

Marketable Securities

Marketable Securities	9 Months Ended
	Sep. 30, 2016
Investments Debt And Equity Securities [Abstract]
Marketable Securities	5. Marketable Securities As of September 30, 2016 and December 31, 2015 the fair value of available-for-sale marketable securities by type of security was as follows: September 30, 2016 (In thousands) Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value U.S. Government obligations $ 17,017 $ 7 $ (1 ) $ 17,023 Commercial Paper 2,996 — — 2,996 Corporate bonds 74,710 2 (35 ) 74,677 $ 94,723 $ 9 $ (36 ) $ 94,696 December 31, 2015 (In thousands) Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value Corporate Bonds $ 55,757 $ 4 $ (101 ) $ 55,660 $ 55,757 $ 4 $ (101 ) $ 55,660 As of September 30, 2016 and December 31, 2015, marketable securities consisted of $92,693,000 and $48,303,000, respectively, of investments that mature within twelve months and $2,003,000 and $7,357,000, respectively, of investments that mature within fifteen months.

Property and Equipment, Net

Property and Equipment, Net	9 Months Ended
	Sep. 30, 2016
Property Plant And Equipment [Abstract]
Property and Equipment, Net	6. Property and Equipment, Net Property and equipment as of September 30, 2016 and December 31, 2015 consisted of the following: (In thousands) September 30, 2016 December 31, 2015 Manufacturing equipment $ 10,099 $ 2,534 Computers, office equipment, and minor computer software 539 393 Software 436 342 Construction—in progress 429 4,134 Furniture and fixtures 402 290 Leasehold improvements 278 239 12,183 7,932 Less: Accumulated depreciation (960 ) (490 ) Total property and equipment, net $ 11,223 $ 7,442 Depreciation expense for the nine months ended September 30, 2016 and 2015 was $700,000 and $130,000, respectively. During the nine months ended September 30, 2016, $2,630,000 of property and equipment was disposed of, resulting in a loss of $2,278,000. Of the $2,630,000 disposed of during the nine months ended September 30, 2016, $2,265,000 was related to manufacturing equipment that will no longer be used due to the Company’s decision to not utilize Evonik Corporation (“Evonik”) for supplies of clinical or commercial Zilretta finished drug product, resulting in a loss of $2,180,000. Construction-in progress is primarily comprised of amounts related to the purchase of a dedicated manufacturing suite for use by the Company’s contract manufacturer of Zilretta finished drug product, Patheon UK Limited (“Patheon”). No property and equipment was disposed of during the nine months ended September 30, 2015.

Accrued Expenses and Other Curr

Accrued Expenses and Other Current Liabilities	9 Months Ended
	Sep. 30, 2016
Payables And Accruals [Abstract]
Accrued Expenses and Other Current Liabilities	7. Accrued Expenses and Other Current Liabilities Accrued expenses and other current liabilities consisted of the following: (In thousands) September 30, 2016 December 31, 2015 Payroll and other employee-related expenses $ 2,018 $ 1,648 Professional services fees 819 434 Other 258 74 Clinical research 204 552 Interest expense 156 81 Contract manufacturing services 149 1,444 Regulatory services 88 64 Consultant fees and expenses 32 70 Total accrued expenses and other current liabilities $ 3,724 $ 4,367

Stock-Based Compensation

Stock-Based Compensation	9 Months Ended
	Sep. 30, 2016
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Stock-Based Compensation	8. Stock-Based Compensation Stock Option Valuation The fair value of each of the Company’s stock option grants is estimated on the date of grant using the Black-Scholes option-pricing model. The Company currently estimates its expected stock volatility based on the historical volatility of its publicly-traded peer companies and expects to continue to do so until such time as it has adequate historical data regarding the volatility of its own publicly-traded stock price. The expected term of the Company’s stock options has been determined utilizing the “simplified” method for awards that qualify as “plain vanilla” options. The expected term of stock options granted to non-employees is equal to the contractual term of the option award. The risk-free interest rate is determined by reference to the U.S. Treasury yield curve in effect at the time of grant of the award for time periods approximately equal to the expected term of the award. Expected dividend yield is based on the fact that the Company has never paid cash dividends and does not expect to pay any cash dividends in the foreseeable future. The relevant data used to determine the value of the stock option grants for the nine months ended September 30, 2016 and 2015 are as follows: Nine months ended September 30, 2016 2015 Risk-free interest rates 1.05-1.90 % 1.49-1.92 % Expected dividend yield 0.00 % 0.00 % Expected term (in years) 6.0 6.0 Expected volatility 79.8-91.1 % 76.4-81.4 % The following table summarizes stock option activity for the nine months ended September 30, 2016: (In thousands, except per share amounts) Shares Under Weighted Exercise Outstanding as of December 31, 2015 1,657 $ 14.28 Granted 948 16.67 Exercised (30 ) 5.52 Cancelled (97 ) 19.16 Outstanding as of September 30, 2016 2,478 $ 15.11 Options vested and expected to vest at September 30, 2016 2,141 $ 14.72 Options exercisable at September 30, 2016 1,078 $ 11.95 In addition to the approximately 948,000 common stock options granted, approximately 205,000 restricted common stock units (“RSUs”) were also granted, of which approximately 10,000 RSUs were cancelled, during the nine months ended September 30, 2016. The RSUs are performance based awards which will begin vesting upon the achievement of a corporate performance based milestone. No outstanding performance awards were vested as of September 30, 2016. The aggregate intrinsic value of options is calculated as the difference between the exercise price of the options and the fair value of the Company’s common stock for those options that had exercise prices lower than the fair value of the Company’s common stock. A total of approximately 30,000 options, with an aggregate intrinsic value of $236,000, were exercised during the nine months ended September 30, 2016. At September 30, 2016 and 2015, there were options for the purchase of approximately 2,478,000 and 1,578,000 shares of the Company’s common stock outstanding, respectively, with a weighted average remaining contractual term of 8.0 and 8.1 years, respectively, and with a weighted average exercise price of $15.11 and $10.32 per share, respectively. The weighted average grant date fair value of options granted during the nine months ended September 30, 2016 and 2015 was $11.90 and $15.67, respectively. Stock-based Compensation The Company recorded stock-based compensation expense related to stock options for the three and nine months ended September 30, 2016 and 2015 as follows: Three months ended September 30, Nine months ended September 30, (In thousands) 2016 2015 2016 2015 Research and development $ 543 $ 332 $ 1,656 $ 941 General and administrative 1,160 789 3,307 2,158 $ 1,703 $ 1,121 $ 4,963 $ 3,099 As of September 30, 2016 unrecognized stock-based compensation expense for stock options outstanding was $11,227,000, which was expected to be recognized over a weighted average period of 2.7 years. As of September 30, 2015, unrecognized stock-based compensation expense for stock options outstanding was $11,500,000, which was expected to be recognized over a weighted average period of 2.7 years. Restricted Stock Units On January 4, 2016, the Company granted RSUs with performance and time-based vesting conditions to certain executives. These RSUs vest, and the underlying shares of common stock become deliverable, in the event the Company receives approval from the U.S. Food and Drug Administration (“FDA”) of a new drug application (“NDA”) for Zilretta (the “ ”

Net Loss per Share

Net Loss per Share	9 Months Ended
	Sep. 30, 2016
Earnings Per Share [Abstract]
Net Loss per Share	9. Net Loss per Share Basic and diluted net loss per share was calculated as follows for the three and nine months ended September 30, 2016 and 2015: For the three months ended September 30, For the nine months ended September 30, (In thousands) 2016 2015 2016 2015 Numerator: Net loss $ (17,782 ) $ (11,136 ) $ (48,782 ) $ (32,747 ) Net loss: $ (17,782 ) $ (11,136 ) $ (48,782 ) $ (32,747 ) Denominator: Weighted average common shares outstanding, basic and diluted 27,524 21,507 23,938 21,478 Net loss per share, basic and diluted $ (0.65 ) $ (0.52 ) $ (2.04 ) $ (1.52 ) Stock options and RSUs covering 2,549,000 and 1,716,000 weighted average shares of common stock were excluded from the computation of diluted net loss per share for the three months ended September 30, 2016 and 2015, respectively, and 2,452,000 and 1,658,000 weighted average shares of common stock were excluded from the computation of diluted net loss per share attributable to common shareholders for the nine months ended September 30, 2016 and 2015, respectively. These equity awards were excluded from the computations because the awards had an anti-dilutive impact due to the net loss incurred for those periods.

Long-term Debt

Long-term Debt	9 Months Ended
	Sep. 30, 2016
Debt Disclosure [Abstract]
Long-term Debt	10. Long-term Debt On August 4, 2015, the Company entered into a credit and security agreement with MidCap Financial Trust, as agent, and MidCap Financial Funding XIII Trust and Silicon Valley Bank, as lenders, (the “Lenders”), to borrow up to $30,000,000 in term loans. The Company concurrently borrowed an initial term loan of $15,000,000 under the facility. The Company granted the Lenders a security interest in substantially all of its personal property, rights and assets, other than intellectual property, to secure the payment of all amounts owed under the credit facility. The Company agreed not to encumber any of its intellectual property without the Lenders’ prior written consent. The Company also agreed to maintain a balance in cash or cash equivalents at Silicon Valley Bank equal to the principal balance of the loan plus 5% for so long as the Company maintains any cash or cash equivalents in non-secured bank accounts. On July 22, 2016, the Company borrowed the remaining $15,000,000 under the credit and security agreement, in the form of a second term loan after receiving positive Phase 3 Zilretta clinical trial data meeting the trial’s primary endpoint and which is sufficient to file an NDA for Zilretta. The second term loan is subject to the same credit terms as the initial term loan under the facility. The credit and security agreement also contains certain representations, warranties, and covenants of the Company as well as a material adverse event clause. As of September 30, 2016, the Company was compliant with all covenants. Borrowings under the credit facility accrue interest monthly at a fixed interest rate of 6.25% per annum. Following an interest-only period of 19 months, principal will be due in 36 equal monthly installments commencing March 1, 2017 and ending February 1, 2020 (the “maturity date”). Upon the maturity date, the Company will be obligated to pay a final payment equal to 9% of the total principal amounts borrowed under the facility. The final payment amount is being accreted to the carrying value of the debt using the effective interest rate method. As of September 30, 2016, the carrying value of the term loan was $30,298,000, of which $6,634,000 was due within 12 months and $23,664,000 was due in greater than 12 months. In connection with the credit and security agreement, the Company incurred debt issuance costs totaling approximately $150,000. These costs are being amortized over the estimated term of the debt using the straight-line method which approximates the effective interest method. The Company elected the early adoption of ASU 2015-03, Interest – Imputation of Interest As of September 30, 2016, annual principal and interest payments due under the 2015 term loan are as follows: Year Aggregate Minimum Payments (in thousands) 2016 (remaining three months) $ 474 2017 10,036 2018 11,082 2019 10,448 2020 4,380 Total $ 36,420 Less interest (3,422 ) Less final payment (2,700 ) Total $ 30,298

Income Taxes

Income Taxes	9 Months Ended
	Sep. 30, 2016
Income Tax Disclosure [Abstract]
Income Taxes	11. Income Taxes Section 382 of the Internal Revenue Code of 1986, as amended (“Section 382”) contains rules that limit the ability of a company that undergoes an ownership change within the meaning of Section 382 to utilize its net operating losses (“NOLs”) and existing tax credits as of the date of such ownership change. Under the rules, such an ownership change is generally any change in ownership of more than 50% of a company’s stock within a rolling three-year period. The rules generally operate by focusing on changes in ownership among stockholders considered by the rules to own, directly or indirectly, 5% or more of the stock of a company and any change in ownership arising from new issuances of stock by the company. During the quarter ended September 30, 2016, the Company completed a Section 382 study through June 30, 2016. The results of this study showed that one historical ownership change within the meaning of Section 382 had occurred on June 8, 2016 in connection with the Company’s 2016 Offering. Although a Section 382 change in ownership has occurred, it is not currently anticipated that a portion of the Company’s NOLs will expire unutilized as a result of this Section 382 limitation. Any subsequent ownership changes as defined by Section 382 may potentially limit the amount of our NOL carryforwards that could be utilized annually to offset any future taxable income. The Company has generated losses since inception and therefore has recorded no income tax benefits for those losses due to its uncertainty of realizing a benefit from those losses.

Foreign Currency

Foreign Currency	9 Months Ended
	Sep. 30, 2016
Foreign Currency [Abstract]
Foreign Currency	12. Foreign Currency The Company maintains a bank account denominated in British Pounds. All foreign currency payables and cash balances are measured at the applicable exchange rate at the end of the reporting period. All associated gains and losses from foreign currency transactions are reflected in the consolidated statements of operations. Foreign currency losses for the three and nine months ended September 30, 2016 was $0.6 million, compared to zero for the three and nine months ended September 30, 2015.

Summary of Significant Accoun19

Summary of Significant Accounting Policies (Policies)	9 Months Ended
	Sep. 30, 2016
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The accompanying condensed consolidated financial statements as of September 30, 2016, and for the three and nine months ended September 30, 2016 and September 30, 2015, have been prepared in accordance with the rules and regulations of the Securities and Exchange Commission (the “SEC”) and Generally Accepted Accounting Principles (“GAAP”) for consolidated financial information including the accounts of the Company and its wholly-owned subsidiary after elimination of all significant intercompany accounts and transactions. Accordingly, they do not include all of the information and footnotes required by GAAP for complete financial statements. In the opinion of management, these condensed consolidated financial statements reflect all adjustments which are necessary for a fair statement of the Company’s financial position and results of its operations, as of and for the periods presented. These condensed consolidated financial statements should be read in conjunction with the consolidated financial statements and notes thereto contained in the Company’s Annual Report on Form 10-K filed with the SEC on March 11, 2016. The information presented in the condensed consolidated financial statements and related notes as of September 30, 2016, and for the three and nine months ended September 30, 2016 and September 30, 2015, is unaudited. The December 31, 2015 consolidated balance sheet included herein was derived from the audited financial statements as of that date, but does not include all disclosures, including notes, required by GAAP for complete financial statements. Interim results for the three and nine months ended September 30, 2016 are not necessarily indicative of the results that may be expected for the fiscal year ending December 31, 2016, or any future period. The accompanying condensed consolidated financial statements have been prepared on a basis which assumes that the Company will continue as a going concern and which contemplates the realization of assets and satisfaction of liabilities and commitments in the normal course of business. The Company has incurred recurring losses and negative cash flows from operations. As of September 30, 2016 and December 31, 2015, the Company had cash, cash equivalents, marketable securities, and long-term investments of $161,505,000 and $118,604,000, respectively. Management believes that current cash, cash equivalents and marketable securities on hand at September 30, 2016 should be sufficient to fund operations for at least the next twelve months. The future viability of the Company is dependent on its ability to raise additional capital to finance its operations, to fund increased research and development costs in order to seek approval for commercialization of its product candidates, and to successfully commercialize Zilretta, if approved. The Company’s failure to raise capital as and when needed would have a negative impact on its financial condition and its ability to pursue its business strategies as this capital is necessary for the Company to perform the research and development activities required to develop and seek approval for commercialization of the Company’s product candidates, to establish a commercial infrastructure in order to generate future revenue streams, and to successfully commercialize Zilretta, if approved. In August 2014, the FASB issued ASU No. 2014-15, Presentation of Financial Statements — Going Concern: Disclosure of Uncertainties about an Entity’s Ability to Continue as a Going Concern In April 2015, the FASB released Accounting Standards Update (“ASU”) 2015-05, Customers Accounting for Fees Paid in a Cloud Computing Arrangement . In November 2015, the FASB issued ASU 2015-17, Income Taxes In February 2016, the FASB issued ASU 2016-02, Leases In March 2016, the FASB released ASU 2016-09, which amends ASC Topic 718, Compensation-Stock Compensation, to require changes to several areas of employee share-based payment accounting in an effort to simplify share-based reporting. The update revises requirements in the following areas: minimum statutory withholding, accounting for income taxes, forfeitures, and intrinsic value accounting for private entities. For public companies, the new rules will become effective for annual reporting periods beginning after December 15, 2016, and interim reporting periods within such annual period. In August 2016, the FASB issued ASU 2016-15, Statement of cash flows
Consolidation	Consolidation The accompanying condensed consolidated financial statements include the Company and its wholly-owned subsidiary, Flexion Securities Corporation, Inc. The Company has eliminated all intercompany transactions for the three and nine months ended September 30, 2016 and the year ended December 31, 2015, the year Flexion Securities Corporation, Inc. was established.
U.S. Government Grant	U.S. Government Grant The Company previously performed research and development for the U.S. Department of Defense under a cost reimbursable grant for a Phase 2 clinical trial investigating Zilretta in active military and medically retired veterans with post-traumatic knee OA. Due to the challenges of enrolling military personnel with post-traumatic knee OA, the Company discontinued the trial and terminated the grant. The related costs incurred under the grant prior to the termination have been included in research and development expense in the statement of operations. The Company was reimbursed and has offset research and development expenses in the statement of operations when invoices for allowable costs were prepared and submitted to the U.S. Department of Defense. Payments under cost reimbursable grants with agencies of the U.S. government are provisional payments subject to adjustment upon audit by the U.S. government.
Accounts Receivable	Accounts Receivable Accounts receivable represents allowable costs under the Company’s now terminated U.S. Government agency grant for which the Company has not yet received reimbursement. The Company invoiced the government on a quarterly basis for reimbursable costs under the grant. Reimbursable costs that have not been invoiced on the last day of the quarter are recorded as unbilled accounts receivable. As of September 30, 2016 there were no unbilled accounts receivable, and as of December 31, 2015, there were unbilled accounts receivable of $95,000.
Use of Estimates	Use of Estimates The preparation of financial statements in conformity with GAAP requires management to make estimates and judgments that may affect the reported amounts of assets and liabilities, expenses and related disclosures. The Company bases estimates and judgments on historical experience and on various other factors that it believes to be reasonable under the circumstances. The most significant estimates in these condensed consolidated financial statements include useful lives with respect to long-lived assets, such as property and equipment and leasehold improvements, accounting for stock-based compensation, and accrued expenses, including clinical research costs. The Company’s actual results may differ from these estimates under different assumptions or conditions. The Company evaluates its estimates on an ongoing basis. Changes in estimates are reflected in reported results in the period in which they become known by the Company’s management.
Property and Equipment	Property and Equipment Property and equipment are stated at cost less accumulated depreciation. Depreciation and amortization expense is recognized using the straight-line method over the following estimated useful lives: Estimated Useful Life (Years) Computers, office equipment, and minor computer software 3 Computer software 7 Manufacturing equipment 7-10 Furniture and fixtures 5 Leasehold improvements are amortized over the shorter of the lease term or the estimated useful life of the related asset. Costs of major additions and improvements are capitalized and depreciated on a straight-line basis over their useful lives. Repairs and maintenance costs are expensed as incurred. Upon retirement or sale, the cost of assets disposed of and the related accumulated depreciation are removed from the accounts and any resulting gain or loss is credited or charged to income. Property and equipment includes construction-in-progress that is not yet in service.
Foreign Currencies	Foreign Currencies The Company maintains a bank account denominated in British Pounds. All foreign currency payables and cash balances are measured at the applicable exchange rate at the end of the reporting period. All associated gains and losses from foreign currency transactions are reflected in the consolidated statements of operations.

Summary of Significant Accoun20

Summary of Significant Accounting Policies (Tables)	9 Months Ended
	Sep. 30, 2016
Accounting Policies [Abstract]
Property Plant and Equipment Estimated Useful Lives	Property and equipment are stated at cost less accumulated depreciation. Depreciation and amortization expense is recognized using the straight-line method over the following estimated useful lives: Estimated Useful Life (Years) Computers, office equipment, and minor computer software 3 Computer software 7 Manufacturing equipment 7-10 Furniture and fixtures 5

Fair Value of Financial Asset21

Fair Value of Financial Assets and Liabilities (Tables)	9 Months Ended
	Sep. 30, 2016
Fair Value Disclosures [Abstract]
Schedule of Assets Measured at Fair Value on Recurring Basis	The following tables present information about the Company’s assets that are measured at fair value on a recurring basis as of September 30, 2016 and December 31, 2015 and indicate the level of the fair value hierarchy utilized to determine such fair value: Fair Value Measurements as of September 30, 2016 Using: (In thousands) Level 1 Level 2 Level 3 Total Assets: Cash equivalents $ — $ 44,540 $ — $ 44,540 Marketable securities — 94,696 — 94,696 $ — $ 139,236 $ — $ 139,236 Fair Value Measurements as of December 31, 2015 Using: (In thousands) Level 1 Level 2 Level 3 Total Assets: Cash equivalents $ — $ 61,534 $ — $ 61,534 Marketable securities — 55,660 — 55,660 $ — $ 117,194 $ — $ 117,194

Marketable Securities (Tables)

Marketable Securities (Tables)	9 Months Ended
	Sep. 30, 2016
Investments Debt And Equity Securities [Abstract]
Summary of Fair Value of Available-for-Sale Marketable Securities by Type of Security	As of September 30, 2016 and December 31, 2015 the fair value of available-for-sale marketable securities by type of security was as follows: September 30, 2016 (In thousands) Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value U.S. Government obligations $ 17,017 $ 7 $ (1 ) $ 17,023 Commercial Paper 2,996 — — 2,996 Corporate bonds 74,710 2 (35 ) 74,677 $ 94,723 $ 9 $ (36 ) $ 94,696 December 31, 2015 (In thousands) Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value Corporate Bonds $ 55,757 $ 4 $ (101 ) $ 55,660 $ 55,757 $ 4 $ (101 ) $ 55,660

Property and Equipment, Net (Ta

Property and Equipment, Net (Tables)	9 Months Ended
	Sep. 30, 2016
Property Plant And Equipment [Abstract]
Components of Property and Equipment	Property and equipment as of September 30, 2016 and December 31, 2015 consisted of the following: (In thousands) September 30, 2016 December 31, 2015 Manufacturing equipment $ 10,099 $ 2,534 Computers, office equipment, and minor computer software 539 393 Software 436 342 Construction—in progress 429 4,134 Furniture and fixtures 402 290 Leasehold improvements 278 239 12,183 7,932 Less: Accumulated depreciation (960 ) (490 ) Total property and equipment, net $ 11,223 $ 7,442

Accrued Expenses and Other Cu24

Accrued Expenses and Other Current Liabilities (Tables)	9 Months Ended
	Sep. 30, 2016
Payables And Accruals [Abstract]
Schedule of Accrued Expenses and Other Current Liabilities	Accrued expenses and other current liabilities consisted of the following: (In thousands) September 30, 2016 December 31, 2015 Payroll and other employee-related expenses $ 2,018 $ 1,648 Professional services fees 819 434 Other 258 74 Clinical research 204 552 Interest expense 156 81 Contract manufacturing services 149 1,444 Regulatory services 88 64 Consultant fees and expenses 32 70 Total accrued expenses and other current liabilities $ 3,724 $ 4,367

Stock-Based Compensation (Table

Stock-Based Compensation (Tables)	9 Months Ended
	Sep. 30, 2016
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Schedule of Relevant Data Used to Estimate Fair Value of Stock Option Grants	The relevant data used to determine the value of the stock option grants for the nine months ended September 30, 2016 and 2015 are as follows: Nine months ended September 30, 2016 2015 Risk-free interest rates 1.05-1.90 % 1.49-1.92 % Expected dividend yield 0.00 % 0.00 % Expected term (in years) 6.0 6.0 Expected volatility 79.8-91.1 % 76.4-81.4 %
Summary of Stock Option Activity	The following table summarizes stock option activity for the nine months ended September 30, 2016: (In thousands, except per share amounts) Shares Under Weighted Exercise Outstanding as of December 31, 2015 1,657 $ 14.28 Granted 948 16.67 Exercised (30 ) 5.52 Cancelled (97 ) 19.16 Outstanding as of September 30, 2016 2,478 $ 15.11 Options vested and expected to vest at September 30, 2016 2,141 $ 14.72 Options exercisable at September 30, 2016 1,078 $ 11.95
Stock-Based Compensation Expense Related to Stock Options	The Company recorded stock-based compensation expense related to stock options for the three and nine months ended September 30, 2016 and 2015 as follows: Three months ended September 30, Nine months ended September 30, (In thousands) 2016 2015 2016 2015 Research and development $ 543 $ 332 $ 1,656 $ 941 General and administrative 1,160 789 3,307 2,158 $ 1,703 $ 1,121 $ 4,963 $ 3,099

Net Loss per Share (Tables)

Net Loss per Share (Tables)	9 Months Ended
	Sep. 30, 2016
Earnings Per Share [Abstract]
Schedule of Basic and Diluted Net Loss per Share	Basic and diluted net loss per share was calculated as follows for the three and nine months ended September 30, 2016 and 2015: For the three months ended September 30, For the nine months ended September 30, (In thousands) 2016 2015 2016 2015 Numerator: Net loss $ (17,782 ) $ (11,136 ) $ (48,782 ) $ (32,747 ) Net loss: $ (17,782 ) $ (11,136 ) $ (48,782 ) $ (32,747 ) Denominator: Weighted average common shares outstanding, basic and diluted 27,524 21,507 23,938 21,478 Net loss per share, basic and diluted $ (0.65 ) $ (0.52 ) $ (2.04 ) $ (1.52 )

Long-term Debt (Tables)

Long-term Debt (Tables)	9 Months Ended
	Sep. 30, 2016
Debt Disclosure [Abstract]
Schedule of Annual Principal and Interest Payments Due Under Term Loan	As of September 30, 2016, annual principal and interest payments due under the 2015 term loan are as follows: Year Aggregate Minimum Payments (in thousands) 2016 (remaining three months) $ 474 2017 10,036 2018 11,082 2019 10,448 2020 4,380 Total $ 36,420 Less interest (3,422 ) Less final payment (2,700 ) Total $ 30,298

Overview and Nature of the Bu28

Overview and Nature of the Business - Additional Information (Detail)	9 Months Ended
	Sep. 30, 2016
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Incorporation date	Nov. 5, 2007

Financing Activities - Addition

Financing Activities - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Millions	Jun. 21, 2016	Jun. 13, 2016	Sep. 30, 2016	Dec. 31, 2015
Class of Stock [Line Items]
Sale of common stock price per share		$ 14
Gross proceeds from initial public offering		$ 77.6
Common stock, shares outstanding			27,527,419	21,570,395
2016 Offering [Member]
Class of Stock [Line Items]
Common stock, shares issued	400,000	5,500,000

Summary of Significant Accoun30

Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($)	Sep. 30, 2016	Dec. 31, 2015
Accounting Policies [Abstract]
Cash and cash equivalents and marketable securities	$ 161,505,000	$ 118,604,000
Unbilled accounts receivable	$ 0	$ 95,000

Summary of Significant Accoun31

Summary of Significant Accounting Policies - Property Plant and Equipment Estimated Useful Lives (Detail)	9 Months Ended
	Sep. 30, 2016
Computers, Office Equipment, and Minor Computer Software [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Estimated Useful Lives	3 years
Computer Software [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Estimated Useful Lives	7 years
Manufacturing Equipment [Member] | Minimum [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Estimated Useful Lives	7 years
Manufacturing Equipment [Member] | Maximum [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Estimated Useful Lives	10 years
Furniture and Fixtures [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Estimated Useful Lives	5 years

Fair Value of Financial Asset32

Fair Value of Financial Assets and Liabilities - Schedule of Assets Measured at Fair Value on Recurring Basis (Detail) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities	$ 92,693	$ 48,303
Fair Value Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	44,540	61,534
Marketable securities	94,696	55,660
Assets, Total	139,236	117,194
Level 2 [Member] | Fair Value Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	44,540	61,534
Marketable securities	94,696	55,660
Assets, Total	$ 139,236	$ 117,194

Fair Value of Financial Asset33

Fair Value of Financial Assets and Liabilities - Additional Information (Detail) - USD ($)	9 Months Ended	12 Months Ended
	Sep. 30, 2016	Dec. 31, 2015
Fair Value Disclosures [Abstract]
Transfers between Level 1, Level 2 and Level 3	$ 0	$ 0

Marketable Securities - Summary

Marketable Securities - Summary of Fair Value of Available-for-Sale Marketable Securities by Type of Security (Detail) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 94,723	$ 55,757
Gross Unrealized Gains	9	4
Gross Unrealized Losses	(36)	(101)
Fair Value	94,696	55,660
U.S. Government Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	17,017
Gross Unrealized Gains	7
Gross Unrealized Losses	(1)
Fair Value	17,023
Commercial Paper [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	2,996
Fair Value	2,996
Corporate Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	74,710	55,757
Gross Unrealized Gains	2	4
Gross Unrealized Losses	(35)	(101)
Fair Value	$ 74,677	$ 55,660

Marketable Securities - Additio

Marketable Securities - Additional Information (Detail) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
Investments Debt And Equity Securities [Abstract]
Marketable securities	$ 92,693	$ 48,303
Marketable securities, noncurrent	$ 2,003	$ 7,357

Property and Equipment, Net - C

Property and Equipment, Net - Components of Property and Equipment (Detail) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
Property, Plant and Equipment [Line Items]
Property and equipment gross	$ 12,183	$ 7,932
Less: Accumulated depreciation	(960)	(490)
Total property and equipment, net	11,223	7,442
Manufacturing Equipment [Member]
Property, Plant and Equipment [Line Items]
Property and equipment gross	10,099	2,534
Construction-in Progress [Member]
Property, Plant and Equipment [Line Items]
Property and equipment gross	429	4,134
Computers, Office Equipment, and Minor Computer Software [Member]
Property, Plant and Equipment [Line Items]
Property and equipment gross	539	393
Furniture and Fixtures [Member]
Property, Plant and Equipment [Line Items]
Property and equipment gross	402	290
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Property and equipment gross	278	239
Software [Member]
Property, Plant and Equipment [Line Items]
Property and equipment gross	$ 436	$ 342

Property and Equipment, Net - A

Property and Equipment, Net - Additional Information (Detail) - USD ($)	9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015
Property, Plant and Equipment [Line Items]
Depreciation	$ 700,000	$ 130,000
Property and equipment disposals	2,630,000	$ 0
Gain (Loss) on sale of property and equipment	(2,278,000)
Manufacturing Equipment [Member]
Property, Plant and Equipment [Line Items]
Property and equipment disposals	2,630,000
Gain (Loss) on sale of property and equipment	(2,180,000)
Manufacturing Equipment [Member] | Evonik Corporation [Member]
Property, Plant and Equipment [Line Items]
Property and equipment disposals	$ 2,265,000

Accrued Expenses and Other Cu38

Accrued Expenses and Other Current Liabilities - Schedule of Accrued Expenses and Other Current Liabilities (Detail) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
Payables And Accruals [Abstract]
Payroll and other employee-related expenses	$ 2,018	$ 1,648
Professional services fees	819	434
Other	258	74
Clinical research	204	552
Interest expense	156	81
Contract manufacturing services	149	1,444
Regulatory services	88	64
Consultant fees and expenses	32	70
Total accrued expenses and other current liabilities	$ 3,724	$ 4,367

Stock-Based Compensation - Sche

Stock-Based Compensation - Schedule of Relevant Data Used to Estimate Fair Value of Stock Option Grants (Detail)	9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Risk-free interest rates, Minimum	1.05%	1.49%
Risk-free interest rates, Maximum	1.90%	1.92%
Expected dividend yield	0.00%	0.00%
Expected term (in years)	6 years	6 years
Expected volatility, Minimum	79.80%	76.40%
Expected volatility, Maximum	91.10%	81.40%

Stock-Based Compensation - Summ

Stock-Based Compensation - Summary of Stock Option Activity (Detail) shares in Thousands	9 Months Ended
	Sep. 30, 2016$ / sharesshares
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Shares Issuable Under Options, Beginning balance | shares	1,657
Shares Issuable Under Options, Granted | shares	948
Shares Issuable Under Options, Exercised | shares	(30)
Shares Issuable Under Options, Cancelled | shares	(97)
Shares Issuable Under Options, Ending balance | shares	2,478
Shares Issuable Under Options, Options vested and expected to vest at September 30, 2016 | shares	2,141
Shares Issuable Under Options, Options exercisable at September 30, 2016 | shares	1,078
Weighted Average Exercise Price, Beginning balance | $ / shares	$ 14.28
Weighted Average Exercise Price, Granted | $ / shares	16.67
Weighted Average Exercise Price, Exercised | $ / shares	5.52
Weighted Average Exercise Price, Cancelled | $ / shares	19.16
Weighted Average Exercise Price, Ending balance | $ / shares	15.11
Weighted Average Exercise Price, Options vested and expected to vest | $ / shares	14.72
Weighted Average Exercise Price, Options exercisable | $ / shares	$ 11.95

Stock-Based Compensation - Addi

Stock-Based Compensation - Additional Information (Detail) - USD ($)	Jan. 04, 2016	Sep. 30, 2016	Sep. 30, 2015	Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock options granted		948,000
Number of options exercised		30,000
Aggregate intrinsic value of stock options exercised		$ 236,000
Options to purchase common stock, outstanding		2,478,000	1,578,000	1,657,000
Weighted average remaining contractual term		8 years	8 years 1 month 6 days
Weighted average exercise price		$ 15.11	$ 10.32	$ 14.28
Weighted average grant date fair value of options granted		$ 11.90	$ 15.67
Unrecognized stock-based compensation expense		$ 11,227,000	$ 11,500,000
Unrecognized compensation costs, weighted-average recognition periods		2 years 8 months 12 days	2 years 8 months 12 days
Performance-Based Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Aggregate number of restricted common stock units granted under performance-based vesting		205,000
Number of RSUs, Cancelled		10,000
Performance based RSUs vested		0
Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Aggregate number of restricted common stock units granted under performance-based vesting	194,400
Grant date fair value of restricted common stock units under performance-based vesting	$ 3,538,000

Stock-Based Compensation - Stoc

Stock-Based Compensation - Stock-Based Compensation Expense Related to Stock Options (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	$ 1,703	$ 1,121	$ 4,963	$ 3,099
Research and Development [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	543	332	1,656	941
General and Administrative [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	$ 1,160	$ 789	$ 3,307	$ 2,158

Net Loss per Share - Schedule o

Net Loss per Share - Schedule of Basic and Diluted Net Loss per Share (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Numerator:
Net loss	$ (17,782)	$ (11,136)	$ (48,782)	$ (32,747)
Net loss:	$ (17,782)	$ (11,136)	$ (48,782)	$ (32,747)
Denominator:
Weighted average common shares outstanding, basic and diluted	27,524	21,507	23,938	21,478
Net loss per share, basic and diluted	$ (0.65)	$ (0.52)	$ (2.04)	$ (1.52)

Net Loss per Share - Additional

Net Loss per Share - Additional Information (Detail) - shares	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Stock Option and RSUs [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from the computation of diluted net loss per share attributable to common shareholders	2,549,000	1,716,000	2,452,000	1,658,000

Long-Term Debt - Additional Inf

Long-Term Debt - Additional Information (Detail) - USD ($)	Jul. 22, 2016	Aug. 04, 2015	Sep. 30, 2016	Dec. 31, 2015
Debt Instrument [Line Items]
Carrying value of term loan			$ 30,298,000
Term loan due within 12 months			6,634,000
Term loan due in greater than 12 months			$ 23,664,000	$ 15,002,000
Debt issuance costs		$ 150,000
Mid Cap Financial Trust [Member] | 2015 Term Loan [Member]
Debt Instrument [Line Items]
Term loan, maximum borrowings		$ 30,000,000
Debt instrument description			The Company also agreed to maintain a balance in cash or cash equivalents at Silicon Valley Bank equal to the principal balance of the loan plus 5%.
Debt instrument percentage of cash or cash equivalents addition to principal balance		5.00%
Debt instrument interest rate		6.25%
Term loan, first periodic payment date		Mar. 1, 2017
Term loan, last periodic payment date		Feb. 1, 2020
Interest on final payment		9.00%
Term loan, payment description			Interest-only period of 19 months, principal will be due in 36 equal monthly installments.
Carrying value of term loan			$ 30,298,000
Term loan due within 12 months			6,634,000
Term loan due in greater than 12 months			$ 23,664,000
Mid Cap Financial Trust [Member] | 2015 Term Loan [Member] | Interest-Only-Strip [Member]
Debt Instrument [Line Items]
Term loan, Interest payment period		19 months
Mid Cap Financial Trust [Member] | 2015 Term Loan [Member] | Principal-Only-Strip [Member]
Debt Instrument [Line Items]
Term loan, Interest payment period		36 months
Mid Cap Financial Trust [Member] | 2015 Term Loan [Member] | Initial Term Loan [Member]
Debt Instrument [Line Items]
Term loan, currently borrowed		$ 15,000,000
Mid Cap Financial Trust [Member] | 2015 Term Loan [Member] | Second Term Loan [Member]
Debt Instrument [Line Items]
Term loan remaining amount borrowed	$ 15,000,000

Long Term Debt - Schedule of An

Long Term Debt - Schedule of Annual Principal and Interest Payments Due Under Term Loan (Detail) $ in Thousands	Sep. 30, 2016USD ($)
Long-term Debt, Fiscal Year Maturity [Abstract]
2016 (remaining three months)	$ 474
2,017	10,036
2,018	11,082
2,019	10,448
2,020	4,380
Total	36,420
Less interest	(3,422)
Less final payment	(2,700)
Total	$ 30,298

Income Taxes - Additional Infor

Income Taxes - Additional Information (Detail)	9 Months Ended
	Sep. 30, 2016USD ($)
Income Tax Disclosure [Abstract]
Limit of utilization of net operating losses (NOLs) and tax credits description	Under the rules, such an ownership change is generally any change in ownership of more than 50% of a company’s stock within a rolling three-year period. The rules generally operate by focusing on changes in ownership among stockholders considered by the rules to own, directly or indirectly, 5% or more of the stock of a company and any change in ownership arising from new issuances of stock by the company.
Income tax benefits	$ 0

Foreign Currency - Additional I

Foreign Currency - Additional Information (Detail) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Foreign Currency [Abstract]
Foreign currency losses	$ 600,000	$ 0	$ 600,000	$ 0