Flexion Therapeutics (FLXN) 10-Q 7 Nov 19 2019 Q3 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	9 Months Ended
	Sep. 30, 2019	Nov. 01, 2019
Cover [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Sep. 30, 2019
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	Q3
Entity Registrant Name	Flexion Therapeutics Inc
Entity Central Index Key	0001419600
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Entity Common Stock Shares Outstanding		38,174,760
Entity Shell Company	false
Entity Small Business	false
Entity Emerging Growth Company	false
Title of 12(b) Security	Common stock, $0.001 par value per share
Trading Symbol	FLXN
Security Exchange Name	NASDAQ
Entity File Number	001-36287
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	26-1388364
Entity Address, Address Line One	10 Mall Road
Entity Address, Address Line Two	Suite 301
Entity Address, City or Town	Burlington
Entity Address, State or Province	MA
Entity Address, Postal Zip Code	01803
City Area Code	(781)
Local Phone Number	305-7777
Document Quarterly Report	true
Document Transition Report	false

Condensed Consolidated Balance

Condensed Consolidated Balance Sheets (Unaudited) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Current assets
Cash and cash equivalents	$ 87,769	$ 87,229
Marketable securities	87,991	171,555
Accounts receivable, net	29,316	13,121
Inventories	14,773	7,637
Prepaid expenses and other current assets	5,235	5,500
Total current assets	225,084	285,042
Property and equipment, net	10,651	10,710
Right-of-use assets	8,618
Total assets	244,353	295,752
Current liabilities
Accounts payable	12,088	12,340
Accrued expenses and other current liabilities	24,419	14,310
Operating lease liabilities	1,283
Current portion of long-term debt		9,967
Total current liabilities	37,790	36,617
Long-term operating lease liability, net	7,865
Long-term debt, net	40,070	3,640
2024 convertible notes, net	151,204	144,879
Other long-term liabilities	251	537
Total liabilities	237,180	185,673
Commitments and contingencies
Preferred stock, $0.001 par value; 10,000,000 shares authorized at September 30, 2019 and December 31, 2018 and 0 shares issued and outstanding at September 30, 2019 and December 31, 2018	0	0
Stockholders' equity
Common stock, $0.001 par value; 100,000,000 shares authorized; 38,152,405 and 37,946,341 shares issued and outstanding, at September 30, 2019 and December 31, 2018, respectively	38	38
Additional paid-in capital	642,087	628,944
Accumulated other comprehensive income (loss)	131	(77)
Accumulated deficit	(635,083)	(518,826)
Total stockholders' equity	7,173	110,079
Total liabilities and stockholders' equity	$ 244,353	$ 295,752

Condensed Consolidated Balanc_2

Condensed Consolidated Balance Sheets (Unaudited) (Parenthetical) - $ / shares	Sep. 30, 2019	Dec. 31, 2018
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	38,152,405	37,946,341
Common stock, shares outstanding	38,152,405	37,946,341

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, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Revenues
Product revenue, net	$ 21,786	$ 6,990	$ 49,303	$ 12,981
Type of Revenue [Extensible List]	us-gaap:ProductMember	us-gaap:ProductMember	us-gaap:ProductMember	us-gaap:ProductMember
Operating expenses
Cost of sales	$ 2,872	$ 1,619	$ 6,032	$ 5,264
Type of Cost, Good or Service [Extensible List]	us-gaap:ProductMember	us-gaap:ProductMember	us-gaap:ProductMember	us-gaap:ProductMember
Research and development	$ 20,938	$ 13,578	$ 52,488	$ 38,223
Selling, general and administrative	32,136	32,804	97,461	90,739
Total operating expenses	55,946	48,001	155,981	134,226
Loss from operations	(34,160)	(41,011)	(106,678)	(121,245)
Other (expense) income
Interest income	721	1,157	2,563	3,572
Interest expense	(4,652)	(3,930)	(12,537)	(11,775)
Other (expense) income	(141)	144	395	364
Total other (expense) income	(4,072)	(2,629)	(9,579)	(7,839)
Net loss	$ (38,232)	$ (43,640)	$ (116,257)	$ (129,084)
Net loss per common share, basic and diluted	$ (1)	$ (1.15)	$ (3.06)	$ (3.42)
Weighted average common shares outstanding, basic and diluted	38,125	37,818	38,043	37,712
Other comprehensive (loss) income:
Unrealized (losses) gains from available-for-sale securities, net of tax of $0	$ (99)	$ 153	$ 208	$ 250
Total other comprehensive (loss) income	(99)	153	208	250
Comprehensive loss	$ (38,331)	$ (43,487)	$ (116,049)	$ (128,834)

Condensed Consolidated Statem_2

Condensed Consolidated Statements of Operations and Comprehensive Loss (Unaudited) (Parenthetical) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Income Statement [Abstract]
Unrealized (losses) gains from available-for-sale securities, tax	$ 0	$ 0	$ 0	$ 0

Condensed Consolidated Statem_3

Condensed Consolidated Statements of Changes in Stockholders' Equity (Unaudited) - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock [Member]	Additional Paid-in-Capital [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Accumulated Deficit [Member]
Balance at Dec. 31, 2017	$ 260,274	$ 38	$ 609,810	$ (407)	$ (349,167)
Balance (in shares) at Dec. 31, 2017		37,611
Issuance of common stock for equity awards	414		414
Issuance of common stock for equity awards (in shares)		22
Stock-based compensation expense	3,657		3,657
Net loss	(41,569)				(41,569)
Other comprehensive income (loss)	(169)			(169)
Balance at Mar. 31, 2018	222,607	$ 38	613,881	(576)	(390,736)
Balance (in shares) at Mar. 31, 2018		37,633
Balance at Dec. 31, 2017	260,274	$ 38	609,810	(407)	(349,167)
Balance (in shares) at Dec. 31, 2017		37,611
Net loss	(129,084)
Other comprehensive income (loss)	250
Balance at Sep. 30, 2018	146,105	$ 38	624,475	(157)	(478,251)
Balance (in shares) at Sep. 30, 2018		37,825
Balance at Mar. 31, 2018	222,607	$ 38	613,881	(576)	(390,736)
Balance (in shares) at Mar. 31, 2018		37,633
Issuance of common stock for equity awards	1,396		1,396
Issuance of common stock for equity awards (in shares)		122
Employee stock purchase plan	1,129		1,129
Employee Stock Purchase Plan (in shares)		53
Stock-based compensation expense	3,984		3,984
Net loss	(43,875)				(43,875)
Other comprehensive income (loss)	266			266
Balance at Jun. 30, 2018	185,507	$ 38	620,390	(310)	(434,611)
Balance (in shares) at Jun. 30, 2018		37,808
Issuance of common stock for equity awards	86		86
Issuance of common stock for equity awards (in shares)		17
Stock-based compensation expense	3,999		3,999
Net loss	(43,640)				(43,640)
Other comprehensive income (loss)	153			153
Balance at Sep. 30, 2018	146,105	$ 38	624,475	(157)	(478,251)
Balance (in shares) at Sep. 30, 2018		37,825
Balance at Dec. 31, 2018	110,079	$ 38	628,944	(77)	(518,826)
Balance (in shares) at Dec. 31, 2018		37,946
Issuance of common stock for equity awards (in shares)		47
Stock-based compensation expense	3,853		3,853
Net loss	(41,538)				(41,538)
Other comprehensive income (loss)	182			182
Balance at Mar. 31, 2019	72,576	$ 38	632,797	105	(560,364)
Balance (in shares) at Mar. 31, 2019		37,993
Balance at Dec. 31, 2018	110,079	$ 38	628,944	(77)	(518,826)
Balance (in shares) at Dec. 31, 2018		37,946
Net loss	(116,257)
Other comprehensive income (loss)	208
Balance at Sep. 30, 2019	7,173	$ 38	642,087	131	(635,083)
Balance (in shares) at Sep. 30, 2019		38,152
Balance at Mar. 31, 2019	72,576	$ 38	632,797	105	(560,364)
Balance (in shares) at Mar. 31, 2019		37,993
Issuance of common stock for equity awards (in shares)		8
Employee stock purchase plan	1,040		1,040
Employee Stock Purchase Plan (in shares)		106
Stock-based compensation expense	4,217		4,217
Net loss	(36,487)				(36,487)
Other comprehensive income (loss)	125			125
Balance at Jun. 30, 2019	41,471	$ 38	638,054	230	(596,851)
Balance (in shares) at Jun. 30, 2019		38,107
Issuance of common stock for equity awards	8		8
Issuance of common stock for equity awards (in shares)		45
Stock-based compensation expense	4,025		4,025
Net loss	(38,232)				(38,232)
Other comprehensive income (loss)	(99)			(99)
Balance at Sep. 30, 2019	$ 7,173	$ 38	$ 642,087	$ 131	$ (635,083)
Balance (in shares) at Sep. 30, 2019		38,152

Condensed Consolidated Statem_4

Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018
Cash flows from operating activities
Net loss	$ (116,257)	$ (129,084)
Adjustments to reconcile net loss to cash used in operating activities
Depreciation	733	1,494
Amortization of right-of-use assets	942
Stock-based compensation expense	12,095	11,640
Non cash interest expense	459
Accretion of discount on marketable securities	(1,155)	(803)
Loss from debt extinguishment	352
Amortization of debt discount and debt issuance costs	6,505	5,786
Premium paid on securities purchased	(27)	(215)
Changes in operating assets and liabilities:
Accounts receivable	(16,195)	(8,388)
Inventory	(6,151)	(3,044)
Prepaid expenses, other current and long-term assets	265	(1,273)
Accounts payable	(576)	2,300
Accrued expenses and other current liabilities	10,033	3,826
Lease liabilities and other long-term liabilities	(839)
Net cash used in operating activities	(109,816)	(117,761)
Cash flows from investing activities
Purchases of property and equipment	(1,118)	(688)
Purchases of marketable securities	(106,105)	(157,116)
Sale and redemption of marketable securities	191,059	269,417
Net cash provided by investing activities	83,836	111,613
Cash flows from financing activities
Proceeds from borrowings under term loan	40,000
Payment of debt issuance costs	(161)
Payments on notes payable	(14,367)	(7,500)
Proceeds from the exercise of stock options	8	1,896
Proceeds from employee stock purchase plan	1,040	1,129
Net cash provided by (used in) financing activities	26,520	(4,475)
Net increase (decrease) in cash, cash equivalents, and restricted cash	540	(10,623)
Cash, cash equivalents, and restricted cash at beginning of period	87,229	128,389
Cash, cash equivalents, and restricted cash at end of period	87,769	117,766
Non-cash investing and financing activities
Right-of-use asset obtained in exchange for operating lease obligation	9,560
Purchases of property and equipment in accounts payable and accrued expenses	1,410	143
Supplemental disclosures of cash flow information
Cash paid for interest	$ 3,991	$ 4,268

Overview and Nature of the Busi

Overview and Nature of the Business	9 Months Ended
	Sep. 30, 2019
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Overview and Nature of the Business	1. Flexion Therapeutics, Inc. (“Flexion” or the “Company”) was incorporated under the laws of the state of Delaware on November 5, 2007. Flexion is a biopharmaceutical company focused on the discovery, development and commercialization of novel, local therapies for the treatment of patients with musculoskeletal conditions, beginning with osteoarthritis, or OA, a type of degenerative arthritis. The Company has an approved product, ZILRETTA ® 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. Successfully commercializing ZILRETTA requires significant sales and marketing efforts and the Company’s pipeline programs may require significant additional research and development efforts, including extensive preclinical and clinical testing. These activities will in turn require significant amounts of capital, qualified personnel and adequate infrastructure. There can be no assurance when, if ever, the Company will realize significant revenue from the sales of ZILRETTA or if the development efforts supporting the Company’s pipeline, including future clinical trials, will be successful.

Summary of Significant Accounti

Summary of Significant Accounting Policies	9 Months Ended
	Sep. 30, 2019
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	2. Basis of Presentation The accompanying condensed consolidated financial statements as of September 30, 2019, and for the three and nine months ended September 30, 2019 and 2018, 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 February 28, 2019. The information presented in the condensed consolidated financial statements and related notes as of September 30, 2019, and for the three and nine months ended September 30, 2019 and 2018, is unaudited. The December 31, 2018 condensed 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, 2019 are not necessarily indicative of the results that may be expected for the fiscal year ending December 31, 2019, 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, 2019, the Company had cash, cash equivalents, and marketable securities of approximately $175.8 million. Management believes that current cash, cash equivalents, and marketable securities on hand at September 30, 2019 should be sufficient to fund operations for at least the next twelve months from the issuance date of these financial statements. The future viability of the Company is dependent on its ability to fund its operations through sales of ZILRETTA, and/or raise additional capital, such as through debt or equity offerings, as needed. This funding is necessary for the Company to support the commercialization of ZILRETTA and to perform the research and development activities required to develop the Company’s other product candidates in order to generate future revenue streams. The Company may not be able to obtain financing on acceptable terms, or at all. If the Company is unable to obtain funding on a timely basis, the Company may need to curtail its operations, including the commercialization of ZILRETTA and research and development activities, which could adversely affect its prospects. Recent Accounting Pronouncements Accounting Standards Recently Adopted In February 2016, the Financial Accounting Standards Board, or FASB, issued ASU 2016-02, Leases As part of its adoption of ASU 2016-02, the Company elected the package of practical expedients which allows it to not reassess (1) whether existing contracts contain leases, (2) the lease classification for existing leases, and (3) whether existing initial direct costs meet the new definition. Consequently, on adoption, the Company recognized lease liabilities of $7.0 million and corresponding right-of-use, or ROU, assets of $6.6 million based on the present value of the remaining minimum rental payments under current leasing standards for existing operating leases. These lease liabilities and ROU assets relate to operating leases only, as the Company concluded that it does not have any finance leases. The difference between the lease liability and the ROU assets upon adoption relates to the deferred rent balance that had been recorded prior to adoption. The Company determined that no cumulative adjustment to retained earnings was required. In June 2018, the FASB issued ASU No. 2018-07, Compensation – Stock Compensation (Topic 718): Improvements to Nonemployee Share-Based Payment Accounting Accounting Standards Recently Issued In June 2016, the FASB issued ASU No. 2016-13, Financial Instruments - Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments In July 2018, the FASB issued ASU No. 2018-13, Fair Value Measurement (Topic 820): Disclosure Framework—Changes to the Disclosure Requirements for Fair Value Measurement Consolidation The accompanying condensed consolidated financial statements include the Company and its wholly-owned subsidiary, Flexion Therapeutics Securities Corporation. The Company has eliminated all intercompany transactions for the three and nine months ended September 30, 2019 and 2018 and the year ended December 31, 2018. Revenue Recognition On October 6, 2017, the U.S. Food and Drug Administration, or FDA, approved ZILRETTA. The Company entered into a limited number of arrangements with specialty distributors and a specialty pharmacy in the U.S. to distribute ZILRETTA. The Company recognizes revenue in accordance with Accounting Standards Codification (“ASC”) Topic 606 - Revenue from Contracts with Customers (“Topic 606”). Under Topic 606, an entity recognizes revenue when its customer obtains control of promised goods or services, in an amount that reflects the consideration which the entity expects to be entitled to in exchange for those goods or services. To determine revenue recognition for arrangements that an entity determines are within the scope of Topic 606, the entity performs the following five steps: (i) identify the contract(s) with a customer, (ii) identify the performance obligations in the contract, (iii) determine the transaction price, (iv) allocate the transaction price to the performance obligations in the contract, and (v) recognize revenue when (or as) the entity satisfies a performance obligation. The Company only applies the five-step model to arrangements that meet the definition of a contract with a customer under Topic 606, including when it is probable that the entity will collect the consideration it is entitled to in exchange for the goods or services it transfers to the customer. At contract inception, once the contract is determined to be within the scope of Topic 606, the Company assesses the goods or services promised within each contract , determines those that are performance obligations, and assesses whether each promised good or service is distinct. The Company then recognizes as revenue the amount of the transaction price that is allocated to the respective performance obligation when (or as) the performance obligation is satisfied. For a complete discussion of accounting for product revenue, see Product Revenue, Net (below). Product Revenue, Net — The Company primarily sells ZILRETTA to specialty distributors and a specialty pharmacy, who then subsequently resell ZILRETTA to physicians, clinics and certain medical centers or hospitals. The Company also contracts directly with healthcare providers and intermediaries such as Group Purchasing Organizations (“GPOs”). In addition, the Company enters into arrangements with government payers that provide for government mandated rebates and chargebacks with respect to the purchase of ZILRETTA. The Company recognizes revenue on product sales when the customer obtains control of the Company's product, which occurs at a point in time (upon delivery to the customer). The Company has determined that the delivery of ZILRETTA to its customers constitutes a single performance obligation. There are no other promises to deliver goods or services beyond what is specified in each accepted customer order. The Company has assessed the existence of a significant financing component in the agreements with its customers. The trade payment terms with customers do not exceed one year and therefore the Company has elected to apply the practical expedient and no amount of consideration has been allocated as a financing component. Product revenues are recorded net of applicable reserves for variable consideration, including discounts and allowances. Transaction Price, including Variable Consideration — Revenues from product sales are recorded at the net sales price (transaction price), which includes estimates of variable consideration for which reserves are established. Components of variable consideration include trade discounts and allowances, product returns, government chargebacks, discounts and rebates, and other incentives, such as voluntary patient assistance, and other fee for service amounts that are detailed within contracts between the Company and its customers relating to the Company’s sale of its products. These reserves, as detailed below, are based on the amounts earned, or to be claimed on the related sales, and are classified as reductions of accounts receivable (if the amount is payable to the customer) or a current liability (if the amount is payable to a party other than a customer). These estimates take into consideration a range of possible outcomes which are probability-weighted in accordance with the expected value method in Topic 606 for relevant factors such as current contractual and statutory requirements, specific known market events and trends, industry data, and forecasted customer buying and payment patterns. Overall, these reserves reflect the Company’s best estimates of the amount of consideration to which it is entitled based on the terms of the respective underlying contracts. The amount of variable consideration which is included in the transaction price may be constrained and is included in the net sales price only to the extent that it is probable that a significant reversal in the amount of the cumulative revenue recognized under the contract will not occur in a future period. Actual amounts of consideration ultimately received may differ from the Company’s estimates. If actual results in the future vary from the Company’s original estimates, the Company will adjust these estimates, which would affect net product revenue and earnings in the period such variances become known. Service Fees and Allowances — The Company compensates its customers and GPOs for sales order management, data, and distribution services. However, the Company has determined such services received to date are not distinct from the Company’s sale of products to the customer and, therefore, these payments have been recorded as a reduction of revenue within the statement of operations and comprehensive loss through September 30, 2019, as well as a reduction to trade receivables, net on the condensed consolidated balance sheets. Product Returns — Consistent with industry practice, the Company generally offers customers a limited right of return for product that has been purchased from the Company based on the product’s expiration date. The Company estimates the amount of its product sales that may be returned by its customers and records this estimate as a reduction of revenue in the period the related product revenue is recognized, as well as within accrued expenses and other current liabilities, net, on the condensed consolidated balance sheets. The Company currently estimates product return liabilities using available industry data and its own sales information, including its visibility into the inventory remaining in the distribution channel. The Company has received an immaterial amount of returns to date and believes that future returns of ZILRETTA will be minimal. The Company’s limited right of return allows for eligible returns of ZILRETTA in the following circumstances: • Shipment errors that were the result of an error by the Company; • Quantity delivered that is greater or less than the quantity ordered; • Product distributed by the Company that is damaged in transit prior to receipt by the customer; • Expired product, previously purchased directly from the Company, that is returned during the period beginning three months prior to the product’s expiration date and ending three months after the product’s expiration date; • Product subject to a recall; and • Product that the Company, at its sole discretion, has specified to be returned. Chargebacks — Chargebacks for fees and discounts to qualified government healthcare providers represent the estimated obligations resulting from contractual commitments to sell products to qualified VA hospitals and 340b entities at prices lower than the list prices charged to customers who directly purchase the product from the Company. The 340b Drug Discount Program is a U.S. federal government program created in 1992 that requires drug manufacturers to provide outpatient drugs to eligible health care organizations and covered entities at significantly reduced prices. Customers charge the Company for the difference between what they pay for the product and the statutory selling price to the qualified government entity. These reserves are established in the same period that the related revenue is recognized, resulting in a reduction of product revenue and trade receivables, net. Chargeback amounts are generally determined at the time of resale to the qualified government healthcare provider by customers, and the Company generally issues credits for such amounts within a few weeks of the customer’s notification to the Company of the resale. Reserves for chargebacks consist of credits that the Company expects to issue for units that remain in the distribution channel inventories at each reporting period-end that the Company expects will be sold to qualified healthcare providers, and chargebacks that customers have claimed, but for which the Company has not yet issued a credit. Government Rebates — The Company is subject to discount obligations under state Medicaid programs and Medicare. These reserves are recorded in the same period the related revenue is recognized, resulting in a reduction of product revenue and the establishment of a current liability which is included in accrued expenses and other current liabilities on the condensed consolidated balance sheets. For Medicare, the Company also estimates the number of patients in the prescription drug coverage gap for whom the Company will owe an additional liability under the Medicare Part D program. The Company estimates its exposure to utilization from the Medicare Part D coverage gap discount program to be immaterial. For Medicaid programs, the Company estimates the portion of sales attributed to Medicaid patients and records a liability for the rebates to be paid to the respective state Medicaid programs. The Company’s liability for these rebates consists of invoices received for claims from prior quarters that have not been paid or for which an invoice has not yet been received, estimates of claims for the current quarter, and estimated future claims that will be made for product that has been recognized as revenue, but which remains in the distribution channel inventories at the end of each reporting period. Purchaser/Provider Discounts and Rebates — Beginning in the third quarter of 2019, the Company began offering rebates to eligible purchasers and healthcare providers that are variable based on volume of product purchased. Rebates are based on actual purchase levels during the rebate purchase period. The Company estimates these rebates and records such estimates in the same period the related revenue is recognized, resulting in a reduction of product revenue and the establishment of a current liability. Other Incentives — Other incentives which the Company offers include voluntary patient assistance programs, such as the co-pay assistance program, which are intended to provide financial assistance to qualified commercially-insured patients with prescription drug co-payments required by payers. The calculation of the accrual for co-pay assistance is based on an estimate of claims and the cost per claim that the Company expects to receive associated with product that has been recognized as revenue, but remains in the distribution channel inventories at the end of each reporting period. The adjustments are recorded in the same period the related revenue is recognized, resulting in a reduction of product revenue and the establishment of a current liability which is included as a component of accrued expenses and other current liabilities on the condensed consolidated balance sheets. To date, the Company’s only source of product revenue has been from the U.S. sales of ZILRETTA, which it began shipping to customers in October 2017. The following table summarizes activity in each of the product revenue allowance and reserve categories for the nine months ended September 30, 2019 and 2018: (In thousands) Service Fees, Allowances and Chargebacks Government Rebates and Other Incentives Product Returns Provider Rebates Total Balance as of December 31, 2018 $ 601 $ 491 $ 125 $ — $ 1,217 Provision related to sales in the current quarter 741 24 57 — 822 Credits and payments made (332 ) (36 ) (33 ) — (401 ) Balance as of March 31, 2019 1,010 479 149 — 1,638 Provision related to sales in the current quarter 1,196 121 92 — 1,409 Credits and payments made (1,157 ) (65 ) (6 ) — (1,228 ) Balance as of June 30, 2019 1,049 535 235 — 1,819 Provision related to sales in the current quarter 1,845 127 136 1,715 3,823 Credits and payments made (1,229 ) (117 ) (6 ) — (1,352 ) Adjustments related to prior period sales — (159 ) — — (159 ) Balance as of September 30, 2019 $ 1,665 $ 386 $ 365 $ 1,715 $ 4,131 Balance as of December 31, 2017 $ 60 $ 15 $ 2 $ — $ 77 Provision related to sales in the current quarter 186 49 12 — 247 Credits and payments made (94 ) — — — (94 ) Balance as of March 31, 2018 152 64 14 — 230 Provision related to sales in the current quarter 300 84 22 — 406 Credits and payments made (214 ) — — — (214 ) Balance as of June 30, 2018 238 148 36 — 422 Provision related to sales in the current quarter 516 158 38 — 712 Credits and payments made (298 ) (6 ) — — (304 ) Balance as of September 30, 2018 $ 456 $ 300 $ 74 $ — $ 830 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, revenue and 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 estimates related to revenue, 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. Leases The Company determines if an arrangement is a lease at contract inception. Operating lease assets represent a right to use an underlying asset for the lease term and operating lease liabilities represent an obligation to make lease payments arising from the lease. Operating lease liabilities with a term greater than one year and their corresponding right-of-use assets are recognized on the balance sheet at the commencement date of the lease based on the present value of lease payments over the expected lease term. Certain adjustments to the right-of-use asset may be required for items such as initial direct costs paid or incentives received. The Company made an accounting policy election to expense leases with a term of one year or less on a straight-line basis over the lease term. To date, the Company has not identified any material short-term leases, either individually or in the aggregate. As the Company’s leases do not provide an implicit rate, the Company utilized the appropriate incremental borrowing rate, which is the rate incurred to borrow on a collateralized basis over a similar term an amount equal to the lease payments in a similar economic environment. The Company estimated the incremental borrowing rate based on a yield curve analysis of companies with a similar credit rating to its own, which was calculated using a number of financial ratios and qualitative considerations of the Company’s business. The yields on the Company’s currently outstanding debt (the 2024 Convertible Notes and term loan) were also used as inputs to the analysis to calculate a spread, adjusted for factors that reflect the profile of secured borrowing over the expected term of the lease. The components of a lease should be split into three categories: lease components (e.g., land, building, etc.), non-lease components (e.g., common area maintenance, utilities, performance of manufacturing services, purchase of inventory, etc.), and non-components (e.g., property taxes, insurance, etc.). Then the fixed contract consideration (including any related to non-components) must be allocated based on fair values to the lease components and non-lease components. Although separation of lease and non-lease components is required, certain practical expedients are available to entities. Entities electing the practical expedient would not separate lease and non-lease components. Rather, they would account for each lease component and the related non-lease component together as a single component. The Company has elected to use this practical expedient for its real estate leases and account for each lease component and related non-lease component as one single component. In contrast, the Company has elected not to apply the practical expedient for its lease of manufacturing space at Patheon and has instead allocated consideration between the lease and non-lease components of the contract. The Company calculated the fair value of the lease component using publicly available information to identify comparable rentals in the same geographic area. The remainder of the consideration was allocated to the non-lease components.

Fair Value of Financial Assets

Fair Value of Financial Assets and Liabilities	9 Months Ended
	Sep. 30, 2019
Fair Value Disclosures [Abstract]
Fair Value of Financial Assets and Liabilities	3. The following tables present information about the Company’s assets that are measured at fair value on a recurring basis as of September 30, 2019 and December 31, 2018 and indicate the level of the fair value hierarchy utilized to determine such fair value: Fair Value Measurements as of September 30, 2019 Using: (In thousands) Level 1 Level 2 Level 3 Total Assets: Cash equivalents $ — $ 35,392 $ — $ 35,392 Marketable securities — 87,991 — 87,991 $ — $ 123,383 $ — $ 123,383 Fair Value Measurements as of December 31, 2018 Using: (In thousands) Level 1 Level 2 Level 3 Total Assets: Cash equivalents $ — $ 57,739 $ — $ 57,739 Marketable securities — 171,555 — 171,555 $ — $ 229,294 $ — $ 229,294 As of September 30, 2019 and December 31, 2018 the Company’s cash equivalents that are invested in money market funds and overnight repurchase contracts are valued based on Level 2 inputs. The Company measures the fair value of marketable securities using Level 2 inputs and primarily relies on quoted prices in active markets for similar marketable securities. Amortization and accretion of discounts and premiums are recorded in other income. The Company had a term loan outstanding under its 2015 credit facility with MidCap Financial Funding XIII Trust and Silicon Valley Bank (the “2015 term loan”). On August 2, 2019, the Company entered into an amended and restated credit and security agreement with Silicon Valley Bank as agent, MidCap Financial Trust, and Flexpoint MCLS Holdings, LLC (collectively, the “Lenders”), providing for a term loan of $40.0 million (the “2019 term loan”). The Company concurrently borrowed the $40.0 million term loan and used $7.7 million of the proceeds to repay the remaining amount owed on the 2015 term loan. On May 2, 2017 the Company issued 3.375% convertible senior notes due 2024 (the “2024 Convertible Notes”) with embedded conversion features. The Company estimated the fair value of the 2024 Convertible Notes using a discounted cash flow approach to derive the value of a debt instrument using the expected cash flows and the estimated yield related to the convertible notes. The significant assumptions used in estimating the expected cash flows were: the estimated market yield based on an implied yield and credit quality analysis of a term loan with similar attributes, and the average implied volatility of the Company’s traded and quoted options available as of May 2, 2017. The Company recorded approximately $136.7 million as the fair value of the liability on May 2, 2017, with a corresponding amount recorded as a discount on the initial issuance of the 2024 Convertible Notes of approximately $64.5 million. The debt discount was recorded to equity and is being amortized to the debt liability over the life of the 2024 Convertible Notes using the effective interest method. The fair value of the 2024 Convertible Notes, which differs from their carrying value, is influenced by interest rates, stock price and stock price volatility and is determined by prices for the 2024 Convertible Notes observed in market trading. The market for trading of the 2024 Convertible Notes is not considered to be an active market and therefore the estimate of fair value is based on Level 2 inputs. The estimated fair value of the 2024 Convertible Notes, face value of $201.3 million, was $187.9 million at September 30, 2019.

Marketable Securities

Marketable Securities	9 Months Ended
	Sep. 30, 2019
Investments Debt And Equity Securities [Abstract]
Marketable Securities	4. As of September 30, 2019 and December 31, 2018 the fair value of available-for-sale marketable securities by type of security was as follows: September 30, 2019 (In thousands) Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value U.S. government obligations $ 39,837 $ 48 $ — $ 39,885 Corporate bonds 48,023 90 (7 ) 48,106 $ 87,860 $ 138 $ (7 ) $ 87,991 December 31, 2018 (In thousands) Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value Commercial paper $ 36,723 $ — $ — $ 36,723 U.S. government obligations 39,910 — (12 ) 39,898 Corporate bonds 94,999 20 (85 ) 94,934 $ 171,632 $ 20 $ (97 ) $ 171,555 As of September 30, 2019 and December 31, 2018, marketable securities consisted of approximately $88.0 million and $171.6 million, respectively, of investments that mature within twelve months. There were no investments with maturities greater than twelve months as of September 30, 2019 and December 31, 2018.

Prepaid Expenses and Other Curr

Prepaid Expenses and Other Current Assets	9 Months Ended
	Sep. 30, 2019
Deferred Costs Capitalized Prepaid And Other Assets Disclosure [Abstract]
Prepaid Expenses and Other Current Assets	5. Prepaid Expenses and Other Current Assets Prepaid expenses and other current assets consisted of the following as of September 30, 2019 and December 31, 2018: (In thousands) September 30, 2019 December 31, 2018 Prepaid expenses $ 4,759 $ 4,717 Deposits 61 66 Interest receivable on marketable securities 415 717 Total prepaid expenses and other current assets $ 5,235 $ 5,500

Inventory

Inventory	9 Months Ended
	Sep. 30, 2019
Inventory Disclosure [Abstract]
Inventory	6. Inventory Inventory consisted of the following as of September 30, 2019 and December 31, 2018: (In thousands) September 30, 2019 December 31, 2018 Raw materials $ 2,531 $ 2,367 Work in process 8,004 3,553 Finished goods 4,238 1,717 Total inventories $ 14,773 $ 7,637 Finished goods manufactured by the Company have a shelf life of approximately 24 months from the date of manufacture. The Company reduces its inventory to net realizable value for potentially excess, dated or obsolete inventory based on an analysis of forecasted demand compared to quantities on hand and any firm purchase orders, as well as product shelf life. During the three and nine months ended September 30, 2019, the Company expensed $0.9 million to cost of sales for unabsorbed manufacturing overhead costs related to the operations of the United Kingdom facility at Patheon U.K. Limited, compared to $1.4 million and $5.0 million in the comparable periods in the prior year. The Company determined that no write-downs to finished goods inventory for potentially excess, dated or obsolete inventory were required.

Property and Equipment, Net

Property and Equipment, Net	9 Months Ended
	Sep. 30, 2019
Property Plant And Equipment [Abstract]
Property and Equipment, Net	7. Property and Equipment, Net Property and equipment, net, as of September 30, 2019 and December 31, 2018 consisted of the following: (In thousands) September 30, 2019 December 31, 2018 Computer and office equipment $ 1,133 $ 1,133 Manufacturing equipment 12,147 12,000 Furniture and fixtures 609 604 Software 455 434 Leasehold improvements 815 815 Construction in progress 2,902 1,416 18,061 16,402 Less: Accumulated depreciation (7,410 ) (5,692 ) Total property and equipment, net $ 10,651 $ 10,710 Depreciation expense for the three and nine months ended September 30, 2019 was approximately $0.2 million and $0.7 million, respectively, compared to $0.4 million and $1.5 million, respectively, for the same periods in the prior year. No property and equipment was disposed of during the nine months ended September 30, 2019. As of September 30, 2019, construction in progress consists primarily of equipment purchases related to the expansion of the Company’s manufacturing capabilities at its contract manufacturer, Patheon U.K. Limited.

Accrued Expenses and Other Curr

Accrued Expenses and Other Current Liabilities	9 Months Ended
	Sep. 30, 2019
Payables And Accruals [Abstract]
Accrued Expenses and Other Current Liabilities	8. Accrued Expenses and Othe Accrued expenses and other current liabilities consisted of the following as of September 30, 2019 and December 31, 2018: (In thousands) September 30, 2019 December 31, 2018 Research and development $ 2,799 $ 1,216 Payroll and other employee-related expenses 10,635 8,207 Professional services fees 4,666 2,544 Accrued interest 3,052 1,195 Product revenue reserves 2,466 616 Accrual for employee stock purchase plan 591 251 Other 210 281 Total accrued expenses and other current liabilities $ 24,419 $ 14,310

Debt

Debt	9 Months Ended
	Sep. 30, 2019
Debt Disclosure [Abstract]
Debt	9. Debt Amended and Restated Credit and Security Agreement Term Loan 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, to borrow up to $30.0 million in term loans. In August 2019, the Company terminated the credit and security agreement and paid off the remaining outstanding balance of principal and accrued and unpaid interest on the 2015 term loan, as well as the $2.7 million final payment. As a result, the Company recorded a debt extinguishment loss of $0.4 million primarily related to the write-off of the unamortized portion of the final payment and unamortized debt issuance costs, which have been recorded as a component of interest expense and other expense, respectively, on the statement of operations for the three and nine months ended September 30, 2019. On August 2, 2019, the Company entered into an amended and restated credit and security agreement (the “amended and restated credit and security agreement”) with Silicon Valley Bank as agent, MidCap Financial Trust, Flexpoint MCLS Holdings, LLC, and the other lenders from time to time party thereto (collectively, the “Lenders”), providing for a term loan of $40.0 million and a revolving credit facility of up to $20.0 million, both of which mature on January 1, 2024 (the “Maturity Date”). The Company concurrently borrowed the $40.0 million term loan and used $7.7 million of the proceeds to repay the remaining amount owed on the 2015 term loan. 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 amended and restated credit and security agreement . The Company agreed not to encumber any of its intellectual property without the Lenders’ prior written consent. The amended and restated credit and security agreement contains certain representations, warranties, and covenants of the Company, including a minimum revenue covenant that will be in effect at any time the Company’s liquidity (defined as cash and cash equivalents held with Silicon Valley Bank) is below $80.0 million. If the revenue covenant becomes applicable and the Company fails to comply with it, or a material adverse change as defined in the agreement occurs, the amounts due under the amended and restated credit and security agreement could be declared immediately due and payable. Borrowings under the 2019 term loan accrue interest monthly at a floating interest rate equal to the greater of the prime rate plus 1.5% or 6.5% per annum. Following an interest-only period of 18 months, principal is due in 36 equal monthly installments commencing February 1, 2021 and ending on the Maturity Date. Upon the Maturity Date, the Company will be obligated to pay a final payment equal to 4.75% 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 straight-line method, which approximates the effective interest method. As of September 30, 2019, the carrying value of the term loan was approximately $40.1 million, all of which is presented as long-term debt in the Company’s condensed consolidated balance sheet as of September 30, 2019. The Company may prepay the term loan at any time by paying the outstanding principal balance, a final payment equal to 4.75% of the term loan amount, all accrued interest and a prepayment fee of 3% of the outstanding term loan amount if repaid in the first year, 2% of the outstanding term loan amount if repaid in the second year, and 1% of the outstanding term loan amount if repaid in the third year of the loan; no prepayment fee is required thereafter. Revolving Credit Facility Borrowings under the revolving credit facility accrue interest monthly at a floating interest rate equal to the greater of the prime rate or 5.50% per annum. In addition to paying interest on any amounts borrowed under the revolving credit facility, the Company owes an unused revolving line facility fee equal to 0.25% per annum of the average unused portion of the revolving line. multiplied by the difference between the total amount available to be borrowed (the “Revolver Commitment Amount”) of $20.0 million and the greater of the average outstanding revolver balance and 25% of the Commitment Amount. The revolving credit facility and any related fees or interest payments will be available to the Company beginning January 1, 2020, subject to certain conditions imposed by the Lenders, including an initial borrowing limitation of up to $10.0 million until the Lenders complete an audit of certain collateral accounts. Beginning on January 1, 2020, if the interest payment on the revolving credit facility is less than the amount of interest that would have been payable had the Company borrowed 25% of the Revolver Commitment Amount, then the Company will be required to pay the difference. The Company may retire the revolving credit facility early, at any time, by paying the outstanding principal balance, all accrued interest and a termination fee equal to 2% of the Revolving Commitment Amount if repaid in the first year, and 1% of the Revolving Commitment Amount if repaid in the second year; with no termination fee thereafter. As of September 30, 2019, annual principal and interest payments due under the 2019 term loan were as follows: Year Aggregate Minimum Payments (in thousands) 2019 679 2020 2,745 2021 14,611 2022 14,816 2023 13,903 Thereafter 3,018 Total $ 49,772 Less interest (7,872 ) Less unamortized portion of final payment (1,830 ) Total $ 40,070 2024 Convertible Notes On May 2, 2017 the Company issued an aggregate of $201.3 million principal amount of the 2024 Convertible Notes. The 2024 Convertible Notes have a maturity date of May 1, 2024, are unsecured and accrue interest at a rate of 3.375% per annum, payable semi-annually on May 1 and November 1 of each year, beginning November 1, 2017. The Company received $194.8 million for the sale of the 2024 Convertible Notes, after deducting fees and expenses of $6.5 million. Upon conversion of the 2024 Convertible Notes, at the election of each holder of a 2024 Convertible Note (the Holder), the note will be convertible into cash, shares of the Company’s common stock, or a combination thereof, at the Company’s election (subject to certain limitations in the 2015 term loan), at a conversion rate of approximately 37.3413 shares of common stock per $1,000 principal amount of the 2024 Convertible Notes, which corresponds to an initial conversion price of approximately $26.78 per share of the Company’s common stock. The conversion rate is subject to adjustment from time to time upon the occurrence of certain events, including, but not limited to, fundamental change events and certain corporate events that occur prior to the maturity date of the notes. In addition, if the Company delivers a notice of redemption, the Company will increase, in certain circumstances, the conversion rate for a Holder who elects to convert its notes in connection with such a corporate event or notice of redemption, as the case may be. At any time prior to the close of business on the business day immediately preceding February 1, 2024, Holders may convert all, or any portion, of the 2024 Convertible Notes at their option only under the following circumstances: (1) during any calendar quarter commencing after the calendar quarter ending on June 30, 2017 (and only during such calendar quarter), if the last reported sale price of the common stock for at least 20 trading days (whether or not consecutive) during a period of 30 consecutive trading days ending on the last trading day of the immediately preceding calendar quarter is greater than or equal to 130% of the conversion price on each applicable trading day; (2) during the five business day period after any ten consecutive trading day period (the “measurement period”) in which the trading price per $1,000 principal amount of notes for each trading day of the measurement period was less than 98% of the product of the last reported sale price of the Company’s common stock and the conversion rate on each such trading day; (3) if the Company calls any or all of the notes for redemption, at any time prior to the close of business on the business day immediately preceding the redemption date; and (4) upon the occurrence of specified corporate events. On or after February 1, 2024, until the close of business on the business day immediately preceding the maturity date, Holders may convert their notes at any time, regardless of the foregoing circumstances. The Company may redeem, for cash, all or any portion of the 2024 Convertible Notes, at its option, on or after May 6, 2020 if the last reported sale price of the Company’s common stock has been at least 130% of the conversion price for at least 20 trading days during any 30 consecutive day trading period, at a redemption price equal to 100% of the principal amount of the 2024 Convertible Notes to be redeemed, plus accrued and unpaid interest, subject to the Holders’ right to convert as described above. The 2024 Convertible Notes are considered convertible debt with a cash conversion feature. Per ASC 470-20, Debt with Conversion and Other Options , The carrying amount of the liability component was calculated by measuring the fair value of a similar liability that does not have an associated convertible feature. The allocation was performed in a manner that reflected our non-convertible debt borrowing rate for similar debt. The equity component of the 2024 Convertible Notes was recognized as a debt discount and represents the difference between the proceeds from the issuance of the 2024 Convertible Notes and the fair value of the liability of the 2024 Convertible Notes on their respective dates of issuance. The excess of the principal amount of the liability component over its carrying amount (“debt discount”) is amortized to interest expense using the effective interest method over seven years. The equity component is not re-measured as long as it continues to meet the conditions for equity classification. In connection with the issuance of the 2024 Convertible Notes, the Company incurred approximately $6.5 million of debt issuance costs, which primarily consisted of underwriting, legal and other professional fees, and allocated these costs to the liability and equity components based on the allocation of the proceeds. Of the total d ebt issuance costs, $4.4 million were allocated to the liability component equity component and is recorded as a reduction to additional paid-in capital. Debt discount and issuance rate three and nine months ended September 30, 2019 respectively, $2.0 million and $5.9 million, respectively, The table below summarizes the carrying value of the 2024 Convertible Notes as of September 30, 2019: ( in thousands Gross proceeds $ 201,250 Portion of proceeds allocated to equity component (additional paid-in capital) (64,541 ) Debt issuance costs (6,470 ) Portion of issuance costs allocated to equity component (additional paid-in capital) 2,075 Amortization of debt discount and debt issuance costs 18,890 Carrying value 2024 Convertible Notes $ 151,204

Stock-Based Compensation

Stock-Based Compensation	9 Months Ended
	Sep. 30, 2019
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Stock-Based Compensation	10. 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 three and nine months ended September 30, 2019 and 2018 were as follows: Three months ended Nine months ended September 30, September 30, 2019 2018 2019 2018 Risk-free interest rates 1.42-1.90% 2.82-2.96% 1.42-2.67% 2.67-2.96% Expected dividend yield 0.00% 0.00% 0.00% 0.00% Expected term (in years) 7.2 6.0 6.2 6.0 Expected volatility 67.1-67.5% 71.3-72.1% 67.1-69.5% 69.8-72.1% The following table summarizes stock option activity for the nine months ended September 30, 2019: (In thousands, except per share amounts) Shares Under Weighted Average Exercise Per Share Outstanding as of December 31, 2018 4,435 $ 19.21 Granted 999 13.45 Exercised (46 ) 0.19 Cancelled (522 ) 20.25 Outstanding as of September 30, 2019 4,866 $ 18.10 Options vested and expected to vest at September 30, 2019 4,866 $ 18.10 Options exercisable at September 30, 2019 2,905 $ 18.32 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. Options to purchase a total of approximately 45,882 shares of the Company’s common stock, with an aggregate intrinsic value of approximately $587,279, were exercised during the nine months ended September 30, 2019. At September 30, 2019 and 2018, there were options for the purchase of approximately 4,865,658 and 4,464,877 shares of the Company’s common stock outstanding, respectively, with a weighted average remaining contractual term of 7.3 years and 7.7 years, respectively, and with a weighted average exercise price of $18.10 and $19.24 per share, respectively. The weighted average grant date fair value of options granted during the nine months ended September 30, 2019 and 2018 was $8.55 and $15.36 per share, respectively. Restricted Stock Units On January 4, 2016, the Company granted 189,300 restricted stock units (“RSUs”) with performance and time-based vesting conditions to certain executives. These RSUs began vesting, and the underlying shares of common stock became deliverable, beginning when ZILRETTA was approved (the “Milestone”). The number of shares eligible for vesting varied based on the timing of achieving the Milestone. As a result of the Milestone being achieved on October 6, 2017, the number of shares of the Company’s common stock earned under these awards was 122,800, subject to ongoing employment with the Company for a period of 2 years. The 122,800 shares had an approximate value of $2.2 million as of the original grant date of which $1.6 million was recognized in the fourth quarter of 2017 upon achieving the Milestone and the remaining $0.6 million is being recognized over a period of two years. During the nine months ended September 30, 2019, the Company awarded 849,706 RSUs to employees at an average grant date fair value of $14.49 per share. The RSUs vest in four substantially equal installments on each of the first four anniversaries of the vesting commencement date, subject to the employee’s continued employment with, or services to, the Company on each vesting date. Compensation expense is recognized on a straight-line basis. The following table summarizes the RSU activity for the nine months ended September 30, 2019: (In thousands, except per share amounts) Number of Shares Weighted Average Grant Date Fair Value Per Share Nonvested balance as of December 31, 2018 252 $ 22.25 Granted 850 14.49 Vested/Released (54 ) 22.96 Cancelled (142 ) 15.81 Nonvested Balance as of September 30, 2019 906 $ 15.94 Stock-based Compensation The Company recorded stock-based compensation expense related to stock options and RSUs and shares purchased under the Employee Stock Purchase Plan for the three and nine months ended September 30, 2019 and 2018 as follows: For the three months ended September 30, For the nine months ended September 30, (In thousands) 2019 2018 2019 2018 Research and development $ 1,304 $ 1,276 $ 3,845 $ 3,563 Selling, general and administrative 2,721 2,723 8,250 8,077 Total $ 4,025 $ 3,999 $ 12,095 $ 11,640 As of September 30, 2019, unrecognized stock-based compensation expense for stock options outstanding was approximately $21.1 million which is expected to be recognized over a weighted average period of 2.3 years. As of September 30, 2019, unrecognized stock-based compensation expense for RSUs outstanding was $11.6 million which is expected to be recognized over a period of 3.1 years.

Net Loss per Share

Net Loss per Share	9 Months Ended
	Sep. 30, 2019
Earnings Per Share [Abstract]
Net Loss per Share	11. Basic and diluted net loss per share attributable to common stockholders was calculated as follows for the three and nine months ended September 30, 2019 and 2018: For the three months ended September 30, For the nine months ended September 30, (In thousands, except per share amounts) 2019 2018 2019 2018 Numerator: Net loss $ (38,232 ) $ (43,640 ) $ (116,257 ) $ (129,084 ) Net loss: $ (38,232 ) $ (43,640 ) $ (116,257 ) $ (129,084 ) Denominator: Weighted average common shares outstanding, basic and diluted 38,125 37,818 38,043 37,712 Net loss per share, basic and diluted $ (1.00 ) $ (1.15 ) $ (3.06 ) $ (3.42 ) The following common stock equivalents were excluded from the calculation of diluted net loss per share for the periods indicated as including them would have an anti-dilutive effect: For the three months ended September 30, For the nine months ended September 30, 2019 2018 2019 2018 Shares issuable upon conversion of the 2024 Convertible Notes 7,515 7,515 7,515 7,515 Stock options 5,157 4,653 5,016 4,466 Restricted stock units 908 297 782 269 Total 13,580 12,465 13,313 12,250

Commitments and Contingencies

Commitments and Contingencies	9 Months Ended
	Sep. 30, 2019
Commitments And Contingencies Disclosure [Abstract]
Commitments and Contingencies	12. Operating Leases Burlington Lease The Company leases approximately 36,500 square feet of office space in Burlington, Massachusetts under a lease that began in May 2013 and was originally scheduled to expire on October 31, 2023 (the “Lease”). Upon adoption of ASU 2016-02, the Company recorded a right-of-use asset and corresponding lease liability for the Lease on January 1, 2019, by calculating the present value of lease payments, discounted at 8.9%, the Company’s estimated incremental borrowing rate, over the 4.8-year remaining term. In June 2019, the Company amended the Lease to add approximately 5,330 square feet of additional office space and extend the term of the Lease through April 30, 2025 (the “Amended Lease”). As a result of the Amended Lease, the total rentable floor area is 41,873 square feet. Starting in August 2019, the Company’s minimum monthly lease payment is approximately $108,000. which increases over the term of the Amended Lease. In addition to the base rent for the office space, the Company is responsible for its share of operating expenses and real estate taxes. The lease commencement date for the additional space, which represents the date the Company first had access to the space, was July 1, 2019. The Company accounted for the Amended Lease as a lease modification that is a separate contract from the original lease and recorded an incremental right-of-use asset and lease liability of $2.5 million, which represents the present value of the lease payments relating to the new space, as well as the lease payments relating to the 18-month extension of the existing space, as of the modification date, discounted at 6.8%. The straight-line lease cost for the Amended Lease (including the expense relating to the original Lease) amounted to $0.5 million and $1.1 million for the three and nine months ended September 30, 2019, respectively, and was included in operating expenses. As of September 30, 2019, the remaining lease term on the Amended Lease was 5.6 years, which includes the 18-month extension resulting from the amendment signed in June 2019. Woburn Lease In February 2017, the Company entered into a five-year lease for laboratory space located in Woburn, Massachusetts with a monthly lease payment of approximately $15,000, which increases over the term of the lease, plus a share of operating expenses. Upon adoption of ASU 2016-02, the Company recorded a right-of-use asset and corresponding lease liability for the Lease on January 1, 2019, by calculating the present value of lease payments, discounted at 8.4%, the Company’s estimated incremental borrowing rate, over the 3.2-year remaining term. The Woburn lease includes an option to extend the term of the lease for two years. Since the Company adopted ASU 2016-02 using the Comparatives under 840 approach, it did not reassess the determination of its operating leases as leases, and therefore no options to extend the lease were included in the calculation of the lease liability as of September 30, 2019. The straight-line lease cost for the Woburn lease amounted to $46 thousand and $139 thousand for the three and nine months ended September 30, 2019, respectively, and was included in operating expenses. As of September 30, 2019, the remaining lease term on the Woburn lease was 2.4 years. Manufacturing and Supply Agreement with Patheon UK Limited In July 2015, the Company and Patheon UK Limited (“Patheon”) entered into a Manufacturing and Supply Agreement (the “Manufacturing Agreement”) and Technical Transfer and Service Agreement (the “Technical Transfer Agreement”) for the manufacture of ZILRETTA. Patheon agreed in the Technical Transfer Agreement to undertake certain transfer activities and construction services needed to prepare Patheon’s United Kingdom facility for the commercial manufacture of ZILRETTA in dedicated manufacturing suites. The Company provided Patheon with certain equipment and materials necessary to manufacture ZILRETTA and pays Patheon a monthly fee for such activities and reimburses Patheon for certain material, equipment and miscellaneous expenses and additional services. The initial term of the Manufacturing Agreement is 10 years from approval by the FDA of the Patheon manufacturing suites for ZILRETTA, or until October 6, 2027. The Company pays a monthly base fee to Patheon for the operation of the manufacturing suites and a per product fee for each vial based upon a forecast of commercial demand. The Company also reimburses Patheon for purchases of materials and equipment made on its behalf, certain nominal expenses and additional services. The Manufacturing Agreement will remain in full effect unless and until it expires or is terminated. Upon termination of the Manufacturing Agreement (other than termination by Flexion in the event that Patheon does not meet the construction and manufacturing milestones or for a breach by Patheon), Flexion will be obligated to pay for the costs incurred by Patheon associated with the removal of Flexion’s manufacturing equipment and for Patheon’s termination costs up to a capped amount. The Manufacturing Agreement with Patheon contains an operating lease for the use of dedicated manufacturing suites. With the adoption of ASU 2016-02, the Company recorded a right-of-use asset and corresponding lease liability for the operating lease. In June 2019, the Company and Patheon amended the Manufacturing Agreement and the Technical Transfer Agreement. The amendment primarily modifies the compensation structure, which is comprised of base fees and per product fees the Company pays to Patheon and does not result in any additional rights of use. The Company accounted for the amendment as a lease modification that is not a separate contract from the original lease. As part of the modification, the Company reassessed whether the contract is or contains a lease and determined that there is an operating lease component for the use of dedicated manufacturing suites. The remainder of the consideration is allocated to the service component. The Company also reassessed the lease liability by calculating the present value of the remaining lease payments as of the modification date, discounted at 6.1%. The modification resulted in an increase to each of the lease liability and right of use asset of $0.5 million. As of September 30, 2019, the remaining lease term on the Patheon lease was 8.1 years. The straight-line lease cost amounted to $54 thousand and $147 thousand for the three and nine months ended September 30, 2019, respectively, and is included in inventory as part of manufacturing overhead. The components of lease expense and related cash flows were as follows: (In thousands) For the three months ended September 30, For the nine months ended September 30, Operating lease cost 2019 2018 2019 2018 Operating lease cost included in operating expenses $ 513 $ — $ 1,251 $ — Operating lease cost included in inventory 54 — 147 — Total operating lease cost 567 — 1,398 — Operating cash flows from operating leases 686 — 1,781 — Maturities of lease liability due under these lease agreements as of September 30, 2019 were as follows: Year Operating Lease Obligations (in thousands) 2019 $ 470 2020 1,968 2021 2,016 2022 1,863 2023 1,871 Thereafter 3,087 Present value of imputed interest (2,530 ) Total $ 8,745 As of December 31, 2018, future minimum lease payments under the Company’s lease obligations under ASC 840 were as follows: Year Aggregate Minimum Payments (in thousands) 2019 1,491 2020 1,533 2021 1,576 2022 1,447 2023 1,203 Total $ 7,250 As of December 31, 2018, future minimum payments under the Company’s agreed obligations under the Manufacturing Agreement with Patheon were as follows: Year Aggregate Minimum Payments (in thousands) 2019 8,027 2020 8,027 2021 8,027 2022 8,027 2023 8,027 2024 and thereafter 30,102 Total $ 70,237 Other Commitments and Contingencies Evonik Supply Agreement In November 2016, the Company entered into a Supply Agreement with Evonik Corporation (“Evonik”) for the purchase of PLGA which is used in the manufacturing of clinical and commercial supply of ZILRETTA. Pursuant to the Supply Agreement, Flexion is obligated to submit rolling monthly forecasts to Evonik for PLGA supply, a portion of which will constitute binding orders. In addition, Flexion agreed to certain minimum purchase requirements, which do not apply (i) during periods in which Evonik is in material breach of the Supply Agreement or is unable to perform its obligations due to a force majeure event, (ii) with respect to orders that Evonik is unable to supply in excess of binding orders, (iii) for orders Evonik is unable to timely deliver or does not deliver conforming product and provides a credit for such order, or (iv) during an uncured material quality failure by Evonik. Flexion agreed to purchase PLGA batches at a specified price per gram in U.S. dollars, subject to adjustment from time to time, including due to changes in price indices and in the event the initial term of the Supply Agreement is extended. The total term of the agreement is five years. Upon termination of the Supply Agreement (other than termination due to the bankruptcy of either Evonik or Flexion) Flexion is obligated to pay the costs associated with the binding supply forecast provided to Evonik. The Supply Agreement will renew for two successive two year terms upon mutual written consent by both parties. FX201 Related Agreements In December 2017, the Company entered into a definitive agreement with GeneQuine Biotherapeutics GmbH (“GeneQuine”) to acquire the global rights to FX201. As part of the asset purchase transaction with GeneQuine, the Company made an upfront payment to GeneQuine of $2.0 million. The Company may also be required to make additional milestone payments during the development of FX201, including up to $8.7 million through Phase 2 proof of concept (PoC) clinical trial and, following successful PoC, up to an additional $54.0 million in development and global regulatory approval milestone payments. The transaction was accounted for as an asset acquisition, as it did not qualify as a business combination. The upfront fee was attributed to the intellectual property acquired and recognized as research and development expense in December 2017 as the FX201 product candidate had not been commercially approved and had no alternative future use. Future milestone payments earned prior to regulatory approval of FX201 will be recognized as research and development expense in the period when the milestone events become probable of being achieved. Future milestones earned subsequent to regulatory approval will be recognized as an intangible asset and amortized to expense over the estimated life of FX201. The first milestone of $750,000 was achieved on October 24, 2018 when the GLP toxicology study was initiated upon the dosing of the first animals. This milestone was recognized as research and development expense in the fourth quarter of 2018. As of September 30, 2019, no other milestones under the arrangement had been achieved. The next milestone of $750,000 was achieved in October 2019 when the FDA accepted the Company’s Investigational New Drug (IND) application for FX201. This milestone will be recognized as research in development expense in the fourth quarter of 2019. As part of the transaction, the Company became the direct licensee of certain underlying Baylor College of Medicine (Baylor) patents and other proprietary rights related to FX201 for human applications. The Baylor license agreement grants the Company an exclusive, royalty-bearing, world-wide right and license (with a right to sublicense) for human applications under its patent and other proprietary rights directly related to FX201, with a similar non-exclusive license to certain Baylor intellectual property rights that are not specific to FX201. The license agreement with Baylor includes a low single-digit royalty on net sales of FX201 and requires the Company to use reasonable efforts to develop FX201 according to timelines set out in the license agreement. In December 2017, the Company also entered into a Master Production Services Agreement with SAFC Carlsbad, Inc., a part of MilliporeSigma, for the manufacturing of preclinical and initial clinical supplies of FX201. FX301 Related Agreements In September 2019, the Company entered into a definitive agreement with Xenon Pharmaceuticals, Inc. (“Xenon”) that provides the Company with the global rights to develop and commercialize Xenon’s NaV1.7 inhibitor (XEN402) formulated for extended release with a novel, Flexion proprietary thermosensitive hydrogel under the Company’s preclinical program known as FX301. As part of the asset purchase transaction with Xenon, the Company made an upfront payment to Xenon of $3.0 million. The Company may also be required to make additional milestone payments during the development of FX301, including up to $9.0 million through initiation of a Phase 2 proof of concept (PoC) clinical trial and, following successful PoC, up to $40.8 million in development and global regulatory approval milestone payments and up to an additional $75.0 million in sales-related milestone payments. The transaction was accounted for as an asset acquisition, as it did not qualify as a business combination. The upfront fee was attributed to the intellectual property acquired and recognized as research and development expense in September 2019 as the FX301 product candidate had not been commercially approved and had no alternative future use. Future milestone payments earned prior to regulatory approval of FX301 will be recognized as research and development expense in the period when the milestone events become probable of being achieved. Future milestones earned subsequent to regulatory approval will be recognized as an intangible asset and amortized to expense over the estimated life of FX301. As of September 30, 2019, no milestones under the arrangement had been achieved. As part of the transaction, the Company became the direct licensee of certain underlying Xenon patents and other proprietary rights related to XEN402 for human applications. The Xenon agreement grants the Company an exclusive, royalty-bearing, world-wide right and license (with a right to sublicense) for human applications under its patents directly related to XEN402, with a similar royalty-free license to other Xenon proprietary rights directly related to XEN402. The agreement with Xenon includes a tiered royalty ranging from mid-single digits to low double digits that is based on aggregate annual net sales of FX301 and requires the Company to use reasonable efforts to develop FX301 according to timelines set out in the agreement.

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	9 Months Ended
	Sep. 30, 2019
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The accompanying condensed consolidated financial statements as of September 30, 2019, and for the three and nine months ended September 30, 2019 and 2018, 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 February 28, 2019. The information presented in the condensed consolidated financial statements and related notes as of September 30, 2019, and for the three and nine months ended September 30, 2019 and 2018, is unaudited. The December 31, 2018 condensed 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, 2019 are not necessarily indicative of the results that may be expected for the fiscal year ending December 31, 2019, 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, 2019, the Company had cash, cash equivalents, and marketable securities of approximately $175.8 million. Management believes that current cash, cash equivalents, and marketable securities on hand at September 30, 2019 should be sufficient to fund operations for at least the next twelve months from the issuance date of these financial statements. The future viability of the Company is dependent on its ability to fund its operations through sales of ZILRETTA, and/or raise additional capital, such as through debt or equity offerings, as needed. This funding is necessary for the Company to support the commercialization of ZILRETTA and to perform the research and development activities required to develop the Company’s other product candidates in order to generate future revenue streams. The Company may not be able to obtain financing on acceptable terms, or at all. If the Company is unable to obtain funding on a timely basis, the Company may need to curtail its operations, including the commercialization of ZILRETTA and research and development activities, which could adversely affect its prospects.
Recent Accounting Pronouncements	Recent Accounting Pronouncements Accounting Standards Recently Adopted In February 2016, the Financial Accounting Standards Board, or FASB, issued ASU 2016-02, Leases As part of its adoption of ASU 2016-02, the Company elected the package of practical expedients which allows it to not reassess (1) whether existing contracts contain leases, (2) the lease classification for existing leases, and (3) whether existing initial direct costs meet the new definition. Consequently, on adoption, the Company recognized lease liabilities of $7.0 million and corresponding right-of-use, or ROU, assets of $6.6 million based on the present value of the remaining minimum rental payments under current leasing standards for existing operating leases. These lease liabilities and ROU assets relate to operating leases only, as the Company concluded that it does not have any finance leases. The difference between the lease liability and the ROU assets upon adoption relates to the deferred rent balance that had been recorded prior to adoption. The Company determined that no cumulative adjustment to retained earnings was required. In June 2018, the FASB issued ASU No. 2018-07, Compensation – Stock Compensation (Topic 718): Improvements to Nonemployee Share-Based Payment Accounting Accounting Standards Recently Issued In June 2016, the FASB issued ASU No. 2016-13, Financial Instruments - Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments In July 2018, the FASB issued ASU No. 2018-13, Fair Value Measurement (Topic 820): Disclosure Framework—Changes to the Disclosure Requirements for Fair Value Measurement
Consolidation	Consolidation The accompanying condensed consolidated financial statements include the Company and its wholly-owned subsidiary, Flexion Therapeutics Securities Corporation. The Company has eliminated all intercompany transactions for the three and nine months ended September 30, 2019 and 2018 and the year ended December 31, 2018.
Revenue Recognition	Revenue Recognition On October 6, 2017, the U.S. Food and Drug Administration, or FDA, approved ZILRETTA. The Company entered into a limited number of arrangements with specialty distributors and a specialty pharmacy in the U.S. to distribute ZILRETTA. The Company recognizes revenue in accordance with Accounting Standards Codification (“ASC”) Topic 606 - Revenue from Contracts with Customers (“Topic 606”). Under Topic 606, an entity recognizes revenue when its customer obtains control of promised goods or services, in an amount that reflects the consideration which the entity expects to be entitled to in exchange for those goods or services. To determine revenue recognition for arrangements that an entity determines are within the scope of Topic 606, the entity performs the following five steps: (i) identify the contract(s) with a customer, (ii) identify the performance obligations in the contract, (iii) determine the transaction price, (iv) allocate the transaction price to the performance obligations in the contract, and (v) recognize revenue when (or as) the entity satisfies a performance obligation. The Company only applies the five-step model to arrangements that meet the definition of a contract with a customer under Topic 606, including when it is probable that the entity will collect the consideration it is entitled to in exchange for the goods or services it transfers to the customer. At contract inception, once the contract is determined to be within the scope of Topic 606, the Company assesses the goods or services promised within each contract , determines those that are performance obligations, and assesses whether each promised good or service is distinct. The Company then recognizes as revenue the amount of the transaction price that is allocated to the respective performance obligation when (or as) the performance obligation is satisfied. For a complete discussion of accounting for product revenue, see Product Revenue, Net (below). Product Revenue, Net — The Company primarily sells ZILRETTA to specialty distributors and a specialty pharmacy, who then subsequently resell ZILRETTA to physicians, clinics and certain medical centers or hospitals. The Company also contracts directly with healthcare providers and intermediaries such as Group Purchasing Organizations (“GPOs”). In addition, the Company enters into arrangements with government payers that provide for government mandated rebates and chargebacks with respect to the purchase of ZILRETTA. The Company recognizes revenue on product sales when the customer obtains control of the Company's product, which occurs at a point in time (upon delivery to the customer). The Company has determined that the delivery of ZILRETTA to its customers constitutes a single performance obligation. There are no other promises to deliver goods or services beyond what is specified in each accepted customer order. The Company has assessed the existence of a significant financing component in the agreements with its customers. The trade payment terms with customers do not exceed one year and therefore the Company has elected to apply the practical expedient and no amount of consideration has been allocated as a financing component. Product revenues are recorded net of applicable reserves for variable consideration, including discounts and allowances. Transaction Price, including Variable Consideration — Revenues from product sales are recorded at the net sales price (transaction price), which includes estimates of variable consideration for which reserves are established. Components of variable consideration include trade discounts and allowances, product returns, government chargebacks, discounts and rebates, and other incentives, such as voluntary patient assistance, and other fee for service amounts that are detailed within contracts between the Company and its customers relating to the Company’s sale of its products. These reserves, as detailed below, are based on the amounts earned, or to be claimed on the related sales, and are classified as reductions of accounts receivable (if the amount is payable to the customer) or a current liability (if the amount is payable to a party other than a customer). These estimates take into consideration a range of possible outcomes which are probability-weighted in accordance with the expected value method in Topic 606 for relevant factors such as current contractual and statutory requirements, specific known market events and trends, industry data, and forecasted customer buying and payment patterns. Overall, these reserves reflect the Company’s best estimates of the amount of consideration to which it is entitled based on the terms of the respective underlying contracts. The amount of variable consideration which is included in the transaction price may be constrained and is included in the net sales price only to the extent that it is probable that a significant reversal in the amount of the cumulative revenue recognized under the contract will not occur in a future period. Actual amounts of consideration ultimately received may differ from the Company’s estimates. If actual results in the future vary from the Company’s original estimates, the Company will adjust these estimates, which would affect net product revenue and earnings in the period such variances become known. Service Fees and Allowances — The Company compensates its customers and GPOs for sales order management, data, and distribution services. However, the Company has determined such services received to date are not distinct from the Company’s sale of products to the customer and, therefore, these payments have been recorded as a reduction of revenue within the statement of operations and comprehensive loss through September 30, 2019, as well as a reduction to trade receivables, net on the condensed consolidated balance sheets. Product Returns — Consistent with industry practice, the Company generally offers customers a limited right of return for product that has been purchased from the Company based on the product’s expiration date. The Company estimates the amount of its product sales that may be returned by its customers and records this estimate as a reduction of revenue in the period the related product revenue is recognized, as well as within accrued expenses and other current liabilities, net, on the condensed consolidated balance sheets. The Company currently estimates product return liabilities using available industry data and its own sales information, including its visibility into the inventory remaining in the distribution channel. The Company has received an immaterial amount of returns to date and believes that future returns of ZILRETTA will be minimal. The Company’s limited right of return allows for eligible returns of ZILRETTA in the following circumstances: • Shipment errors that were the result of an error by the Company; • Quantity delivered that is greater or less than the quantity ordered; • Product distributed by the Company that is damaged in transit prior to receipt by the customer; • Expired product, previously purchased directly from the Company, that is returned during the period beginning three months prior to the product’s expiration date and ending three months after the product’s expiration date; • Product subject to a recall; and • Product that the Company, at its sole discretion, has specified to be returned. Chargebacks — Chargebacks for fees and discounts to qualified government healthcare providers represent the estimated obligations resulting from contractual commitments to sell products to qualified VA hospitals and 340b entities at prices lower than the list prices charged to customers who directly purchase the product from the Company. The 340b Drug Discount Program is a U.S. federal government program created in 1992 that requires drug manufacturers to provide outpatient drugs to eligible health care organizations and covered entities at significantly reduced prices. Customers charge the Company for the difference between what they pay for the product and the statutory selling price to the qualified government entity. These reserves are established in the same period that the related revenue is recognized, resulting in a reduction of product revenue and trade receivables, net. Chargeback amounts are generally determined at the time of resale to the qualified government healthcare provider by customers, and the Company generally issues credits for such amounts within a few weeks of the customer’s notification to the Company of the resale. Reserves for chargebacks consist of credits that the Company expects to issue for units that remain in the distribution channel inventories at each reporting period-end that the Company expects will be sold to qualified healthcare providers, and chargebacks that customers have claimed, but for which the Company has not yet issued a credit. Government Rebates — The Company is subject to discount obligations under state Medicaid programs and Medicare. These reserves are recorded in the same period the related revenue is recognized, resulting in a reduction of product revenue and the establishment of a current liability which is included in accrued expenses and other current liabilities on the condensed consolidated balance sheets. For Medicare, the Company also estimates the number of patients in the prescription drug coverage gap for whom the Company will owe an additional liability under the Medicare Part D program. The Company estimates its exposure to utilization from the Medicare Part D coverage gap discount program to be immaterial. For Medicaid programs, the Company estimates the portion of sales attributed to Medicaid patients and records a liability for the rebates to be paid to the respective state Medicaid programs. The Company’s liability for these rebates consists of invoices received for claims from prior quarters that have not been paid or for which an invoice has not yet been received, estimates of claims for the current quarter, and estimated future claims that will be made for product that has been recognized as revenue, but which remains in the distribution channel inventories at the end of each reporting period. Purchaser/Provider Discounts and Rebates — Beginning in the third quarter of 2019, the Company began offering rebates to eligible purchasers and healthcare providers that are variable based on volume of product purchased. Rebates are based on actual purchase levels during the rebate purchase period. The Company estimates these rebates and records such estimates in the same period the related revenue is recognized, resulting in a reduction of product revenue and the establishment of a current liability. Other Incentives — Other incentives which the Company offers include voluntary patient assistance programs, such as the co-pay assistance program, which are intended to provide financial assistance to qualified commercially-insured patients with prescription drug co-payments required by payers. The calculation of the accrual for co-pay assistance is based on an estimate of claims and the cost per claim that the Company expects to receive associated with product that has been recognized as revenue, but remains in the distribution channel inventories at the end of each reporting period. The adjustments are recorded in the same period the related revenue is recognized, resulting in a reduction of product revenue and the establishment of a current liability which is included as a component of accrued expenses and other current liabilities on the condensed consolidated balance sheets. To date, the Company’s only source of product revenue has been from the U.S. sales of ZILRETTA, which it began shipping to customers in October 2017. The following table summarizes activity in each of the product revenue allowance and reserve categories for the nine months ended September 30, 2019 and 2018: (In thousands) Service Fees, Allowances and Chargebacks Government Rebates and Other Incentives Product Returns Provider Rebates Total Balance as of December 31, 2018 $ 601 $ 491 $ 125 $ — $ 1,217 Provision related to sales in the current quarter 741 24 57 — 822 Credits and payments made (332 ) (36 ) (33 ) — (401 ) Balance as of March 31, 2019 1,010 479 149 — 1,638 Provision related to sales in the current quarter 1,196 121 92 — 1,409 Credits and payments made (1,157 ) (65 ) (6 ) — (1,228 ) Balance as of June 30, 2019 1,049 535 235 — 1,819 Provision related to sales in the current quarter 1,845 127 136 1,715 3,823 Credits and payments made (1,229 ) (117 ) (6 ) — (1,352 ) Adjustments related to prior period sales — (159 ) — — (159 ) Balance as of September 30, 2019 $ 1,665 $ 386 $ 365 $ 1,715 $ 4,131 Balance as of December 31, 2017 $ 60 $ 15 $ 2 $ — $ 77 Provision related to sales in the current quarter 186 49 12 — 247 Credits and payments made (94 ) — — — (94 ) Balance as of March 31, 2018 152 64 14 — 230 Provision related to sales in the current quarter 300 84 22 — 406 Credits and payments made (214 ) — — — (214 ) Balance as of June 30, 2018 238 148 36 — 422 Provision related to sales in the current quarter 516 158 38 — 712 Credits and payments made (298 ) (6 ) — — (304 ) Balance as of September 30, 2018 $ 456 $ 300 $ 74 $ — $ 830
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, revenue and 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 estimates related to revenue, 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.
Leases	Leases The Company determines if an arrangement is a lease at contract inception. Operating lease assets represent a right to use an underlying asset for the lease term and operating lease liabilities represent an obligation to make lease payments arising from the lease. Operating lease liabilities with a term greater than one year and their corresponding right-of-use assets are recognized on the balance sheet at the commencement date of the lease based on the present value of lease payments over the expected lease term. Certain adjustments to the right-of-use asset may be required for items such as initial direct costs paid or incentives received. The Company made an accounting policy election to expense leases with a term of one year or less on a straight-line basis over the lease term. To date, the Company has not identified any material short-term leases, either individually or in the aggregate. As the Company’s leases do not provide an implicit rate, the Company utilized the appropriate incremental borrowing rate, which is the rate incurred to borrow on a collateralized basis over a similar term an amount equal to the lease payments in a similar economic environment. The Company estimated the incremental borrowing rate based on a yield curve analysis of companies with a similar credit rating to its own, which was calculated using a number of financial ratios and qualitative considerations of the Company’s business. The yields on the Company’s currently outstanding debt (the 2024 Convertible Notes and term loan) were also used as inputs to the analysis to calculate a spread, adjusted for factors that reflect the profile of secured borrowing over the expected term of the lease. The components of a lease should be split into three categories: lease components (e.g., land, building, etc.), non-lease components (e.g., common area maintenance, utilities, performance of manufacturing services, purchase of inventory, etc.), and non-components (e.g., property taxes, insurance, etc.). Then the fixed contract consideration (including any related to non-components) must be allocated based on fair values to the lease components and non-lease components. Although separation of lease and non-lease components is required, certain practical expedients are available to entities. Entities electing the practical expedient would not separate lease and non-lease components. Rather, they would account for each lease component and the related non-lease component together as a single component. The Company has elected to use this practical expedient for its real estate leases and account for each lease component and related non-lease component as one single component. In contrast, the Company has elected not to apply the practical expedient for its lease of manufacturing space at Patheon and has instead allocated consideration between the lease and non-lease components of the contract. The Company calculated the fair value of the lease component using publicly available information to identify comparable rentals in the same geographic area. The remainder of the consideration was allocated to the non-lease components.

Summary of Significant Accoun_3

Summary of Significant Accounting Policies (Tables)	9 Months Ended
	Sep. 30, 2019
Accounting Policies [Abstract]
Summary of Product Revenue Allowance And Reserve Categories	The following table summarizes activity in each of the product revenue allowance and reserve categories for the nine months ended September 30, 2019 and 2018: (In thousands) Service Fees, Allowances and Chargebacks Government Rebates and Other Incentives Product Returns Provider Rebates Total Balance as of December 31, 2018 $ 601 $ 491 $ 125 $ — $ 1,217 Provision related to sales in the current quarter 741 24 57 — 822 Credits and payments made (332 ) (36 ) (33 ) — (401 ) Balance as of March 31, 2019 1,010 479 149 — 1,638 Provision related to sales in the current quarter 1,196 121 92 — 1,409 Credits and payments made (1,157 ) (65 ) (6 ) — (1,228 ) Balance as of June 30, 2019 1,049 535 235 — 1,819 Provision related to sales in the current quarter 1,845 127 136 1,715 3,823 Credits and payments made (1,229 ) (117 ) (6 ) — (1,352 ) Adjustments related to prior period sales — (159 ) — — (159 ) Balance as of September 30, 2019 $ 1,665 $ 386 $ 365 $ 1,715 $ 4,131 Balance as of December 31, 2017 $ 60 $ 15 $ 2 $ — $ 77 Provision related to sales in the current quarter 186 49 12 — 247 Credits and payments made (94 ) — — — (94 ) Balance as of March 31, 2018 152 64 14 — 230 Provision related to sales in the current quarter 300 84 22 — 406 Credits and payments made (214 ) — — — (214 ) Balance as of June 30, 2018 238 148 36 — 422 Provision related to sales in the current quarter 516 158 38 — 712 Credits and payments made (298 ) (6 ) — — (304 ) Balance as of September 30, 2018 $ 456 $ 300 $ 74 $ — $ 830
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 Asset_2

Fair Value of Financial Assets and Liabilities (Tables)	9 Months Ended
	Sep. 30, 2019
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, 2019 and December 31, 2018 and indicate the level of the fair value hierarchy utilized to determine such fair value: Fair Value Measurements as of September 30, 2019 Using: (In thousands) Level 1 Level 2 Level 3 Total Assets: Cash equivalents $ — $ 35,392 $ — $ 35,392 Marketable securities — 87,991 — 87,991 $ — $ 123,383 $ — $ 123,383 Fair Value Measurements as of December 31, 2018 Using: (In thousands) Level 1 Level 2 Level 3 Total Assets: Cash equivalents $ — $ 57,739 $ — $ 57,739 Marketable securities — 171,555 — 171,555 $ — $ 229,294 $ — $ 229,294

Marketable Securities (Tables)

Marketable Securities (Tables)	9 Months Ended
	Sep. 30, 2019
Investments Debt And Equity Securities [Abstract]
Summary of Fair Value of Available-for-Sale Marketable Securities by Type of Security	As of September 30, 2019 and December 31, 2018 the fair value of available-for-sale marketable securities by type of security was as follows: September 30, 2019 (In thousands) Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value U.S. government obligations $ 39,837 $ 48 $ — $ 39,885 Corporate bonds 48,023 90 (7 ) 48,106 $ 87,860 $ 138 $ (7 ) $ 87,991 December 31, 2018 (In thousands) Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value Commercial paper $ 36,723 $ — $ — $ 36,723 U.S. government obligations 39,910 — (12 ) 39,898 Corporate bonds 94,999 20 (85 ) 94,934 $ 171,632 $ 20 $ (97 ) $ 171,555

Prepaid Expenses and Other Cu_2

Prepaid Expenses and Other Current Assets (Tables)	9 Months Ended
	Sep. 30, 2019
Deferred Costs Capitalized Prepaid And Other Assets Disclosure [Abstract]
Prepaid Expenses and Other Current Assets	Prepaid expenses and other current assets consisted of the following as of September 30, 2019 and December 31, 2018: (In thousands) September 30, 2019 December 31, 2018 Prepaid expenses $ 4,759 $ 4,717 Deposits 61 66 Interest receivable on marketable securities 415 717 Total prepaid expenses and other current assets $ 5,235 $ 5,500

Inventory (Tables)

Inventory (Tables)	9 Months Ended
	Sep. 30, 2019
Inventory Disclosure [Abstract]
Schedule of Inventory	Inventory consisted of the following as of September 30, 2019 and December 31, 2018: (In thousands) September 30, 2019 December 31, 2018 Raw materials $ 2,531 $ 2,367 Work in process 8,004 3,553 Finished goods 4,238 1,717 Total inventories $ 14,773 $ 7,637

Property and Equipment, Net (Ta

Property and Equipment, Net (Tables)	9 Months Ended
	Sep. 30, 2019
Property Plant And Equipment [Abstract]
Components of Property and Equipment	Property and equipment, net, as of September 30, 2019 and December 31, 2018 consisted of the following: (In thousands) September 30, 2019 December 31, 2018 Computer and office equipment $ 1,133 $ 1,133 Manufacturing equipment 12,147 12,000 Furniture and fixtures 609 604 Software 455 434 Leasehold improvements 815 815 Construction in progress 2,902 1,416 18,061 16,402 Less: Accumulated depreciation (7,410 ) (5,692 ) Total property and equipment, net $ 10,651 $ 10,710

Accrued Expenses and Other Cu_2

Accrued Expenses and Other Current Liabilities (Tables)	9 Months Ended
	Sep. 30, 2019
Payables And Accruals [Abstract]
Schedule of Accrued Expenses and Other Current Liabilities	Accrued expenses and other current liabilities consisted of the following as of September 30, 2019 and December 31, 2018: (In thousands) September 30, 2019 December 31, 2018 Research and development $ 2,799 $ 1,216 Payroll and other employee-related expenses 10,635 8,207 Professional services fees 4,666 2,544 Accrued interest 3,052 1,195 Product revenue reserves 2,466 616 Accrual for employee stock purchase plan 591 251 Other 210 281 Total accrued expenses and other current liabilities $ 24,419 $ 14,310

Debt (Tables)

Debt (Tables)	9 Months Ended
	Sep. 30, 2019
Debt Disclosure [Abstract]
Schedule of Annual Principal and Interest Payments Due Under Term Loan	As of September 30, 2019, annual principal and interest payments due under the 2019 term loan were as follows: Year Aggregate Minimum Payments (in thousands) 2019 679 2020 2,745 2021 14,611 2022 14,816 2023 13,903 Thereafter 3,018 Total $ 49,772 Less interest (7,872 ) Less unamortized portion of final payment (1,830 ) Total $ 40,070
Summary of Carrying Value of Convertible Notes	The table below summarizes the carrying value of the 2024 Convertible Notes as of September 30, 2019: ( in thousands Gross proceeds $ 201,250 Portion of proceeds allocated to equity component (additional paid-in capital) (64,541 ) Debt issuance costs (6,470 ) Portion of issuance costs allocated to equity component (additional paid-in capital) 2,075 Amortization of debt discount and debt issuance costs 18,890 Carrying value 2024 Convertible Notes $ 151,204

Stock-Based Compensation (Table

Stock-Based Compensation (Tables)	9 Months Ended
	Sep. 30, 2019
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 three and nine months ended September 30, 2019 and 2018 were as follows: Three months ended Nine months ended September 30, September 30, 2019 2018 2019 2018 Risk-free interest rates 1.42-1.90% 2.82-2.96% 1.42-2.67% 2.67-2.96% Expected dividend yield 0.00% 0.00% 0.00% 0.00% Expected term (in years) 7.2 6.0 6.2 6.0 Expected volatility 67.1-67.5% 71.3-72.1% 67.1-69.5% 69.8-72.1%
Summary of Stock Option Activity	The following table summarizes stock option activity for the nine months ended September 30, 2019: (In thousands, except per share amounts) Shares Under Weighted Average Exercise Per Share Outstanding as of December 31, 2018 4,435 $ 19.21 Granted 999 13.45 Exercised (46 ) 0.19 Cancelled (522 ) 20.25 Outstanding as of September 30, 2019 4,866 $ 18.10 Options vested and expected to vest at September 30, 2019 4,866 $ 18.10 Options exercisable at September 30, 2019 2,905 $ 18.32
Summary of of RSU Activity	The following table summarizes the RSU activity for the nine months ended September 30, 2019: (In thousands, except per share amounts) Number of Shares Weighted Average Grant Date Fair Value Per Share Nonvested balance as of December 31, 2018 252 $ 22.25 Granted 850 14.49 Vested/Released (54 ) 22.96 Cancelled (142 ) 15.81 Nonvested Balance as of September 30, 2019 906 $ 15.94
Stock-Based Compensation Expense Related to Stock Options, and RSUs and Shares Purchased Under Employee Stock Purchase Plan	The Company recorded stock-based compensation expense related to stock options and RSUs and shares purchased under the Employee Stock Purchase Plan for the three and nine months ended September 30, 2019 and 2018 as follows: For the three months ended September 30, For the nine months ended September 30, (In thousands) 2019 2018 2019 2018 Research and development $ 1,304 $ 1,276 $ 3,845 $ 3,563 Selling, general and administrative 2,721 2,723 8,250 8,077 Total $ 4,025 $ 3,999 $ 12,095 $ 11,640

Net Loss per Share (Tables)

Net Loss per Share (Tables)	9 Months Ended
	Sep. 30, 2019
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 for the three and nine months ended September 30, 2019 and 2018: For the three months ended September 30, For the nine months ended September 30, (In thousands, except per share amounts) 2019 2018 2019 2018 Numerator: Net loss $ (38,232 ) $ (43,640 ) $ (116,257 ) $ (129,084 ) Net loss: $ (38,232 ) $ (43,640 ) $ (116,257 ) $ (129,084 ) Denominator: Weighted average common shares outstanding, basic and diluted 38,125 37,818 38,043 37,712 Net loss per share, basic and diluted $ (1.00 ) $ (1.15 ) $ (3.06 ) $ (3.42 )
Schedule of Common Stock Equivalents Excluded from Calculation of Diluted Net Loss Per Share, as Including them Would have Anti-dilutive Effect	The following common stock equivalents were excluded from the calculation of diluted net loss per share for the periods indicated as including them would have an anti-dilutive effect: For the three months ended September 30, For the nine months ended September 30, 2019 2018 2019 2018 Shares issuable upon conversion of the 2024 Convertible Notes 7,515 7,515 7,515 7,515 Stock options 5,157 4,653 5,016 4,466 Restricted stock units 908 297 782 269 Total 13,580 12,465 13,313 12,250

Commitments and Contingencies (

Commitments and Contingencies (Tables)	9 Months Ended
	Sep. 30, 2019
Commitments And Contingencies Disclosure [Abstract]
Components of Lease Expense and Related Cash Flows	The components of lease expense and related cash flows were as follows: (In thousands) For the three months ended September 30, For the nine months ended September 30, Operating lease cost 2019 2018 2019 2018 Operating lease cost included in operating expenses $ 513 $ — $ 1,251 $ — Operating lease cost included in inventory 54 — 147 — Total operating lease cost 567 — 1,398 — Operating cash flows from operating leases 686 — 1,781 —
Schedule of Maturities of Lease Liability Due Under Lease Agreements	Maturities of lease liability due under these lease agreements as of September 30, 2019 were as follows: Year Operating Lease Obligations (in thousands) 2019 $ 470 2020 1,968 2021 2,016 2022 1,863 2023 1,871 Thereafter 3,087 Present value of imputed interest (2,530 ) Total $ 8,745
Future Minimum Lease Payments under Operating Leases	As of December 31, 2018, future minimum lease payments under the Company’s lease obligations under ASC 840 were as follows: Year Aggregate Minimum Payments (in thousands) 2019 1,491 2020 1,533 2021 1,576 2022 1,447 2023 1,203 Total $ 7,250
Schedule of Future Minimum Payments under Manufacturing Agreement with Patheon	As of December 31, 2018, future minimum payments under the Company’s agreed obligations under the Manufacturing Agreement with Patheon were as follows: Year Aggregate Minimum Payments (in thousands) 2019 8,027 2020 8,027 2021 8,027 2022 8,027 2023 8,027 2024 and thereafter 30,102 Total $ 70,237

Overview and Nature of the Bu_2

Overview and Nature of the Business - Additional Information (Detail)	9 Months Ended
	Sep. 30, 2019
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Incorporation date	Nov. 5, 2007

Summary of Significant Accoun_4

Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2019	Jan. 01, 2019
Summary Of Significant Accounting Policies [Line Items]
Cash and cash equivalents, marketable securities and long term investments	$ 175,800
Operating lease liabilities		$ 7,000
Operating lease, right-of-use asset	$ 8,618	$ 6,600
ZILRETTA [Member]
Summary Of Significant Accounting Policies [Line Items]
Product return, period prior to expiration	3 months
Product return, period after expiration	3 months
Maximum [Member]
Summary Of Significant Accounting Policies [Line Items]
Trade Payment Term	1 year

Summary of Significant Accoun_5

Summary of Significant Accounting Policies - Summary of Product Revenue Allowance And Reserve Categories (Detail) - USD ($) $ in Thousands	3 Months Ended
	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018
Service Fees, Allowances and Chargebacks [Member]
Summary Of Significant Accounting Policies [Line Items]
Beginning Balance	$ 1,049	$ 1,010	$ 601	$ 238	$ 152	$ 60
Provision related to sales in the current quarter	1,845	1,196	741	516	300	186
Credits and payments made	(1,229)	(1,157)	(332)	(298)	(214)	(94)
Ending Balance	1,665	1,049	1,010	456	238	152
Government Rebates and Other Incentives [Member]
Summary Of Significant Accounting Policies [Line Items]
Beginning Balance	535	479	491	148	64	15
Provision related to sales in the current quarter	127	121	24	158	84	49
Credits and payments made	(117)	(65)	(36)	(6)
Adjustments related to prior period sales	(159)
Ending Balance	386	535	479	300	148	64
Product Returns [Member]
Summary Of Significant Accounting Policies [Line Items]
Beginning Balance	235	149	125	36	14	2
Provision related to sales in the current quarter	136	92	57	38	22	12
Credits and payments made	(6)	(6)	(33)
Ending Balance	365	235	149	74	36	14
Provider Rebates [Member]
Summary Of Significant Accounting Policies [Line Items]
Provision related to sales in the current quarter	1,715
Ending Balance	1,715
Product Revenue Allowance and Reserve [Member]
Summary Of Significant Accounting Policies [Line Items]
Beginning Balance	1,819	1,638	1,217	422	230	77
Provision related to sales in the current quarter	3,823	1,409	822	712	406	247
Credits and payments made	(1,352)	(1,228)	(401)	(304)	(214)	(94)
Adjustments related to prior period sales	(159)
Ending Balance	$ 4,131	$ 1,819	$ 1,638	$ 830	$ 422	$ 230

Summary of Significant Accoun_6

Summary of Significant Accounting Policies - Property Plant and Equipment Estimated Useful Lives (Detail)	9 Months Ended
	Sep. 30, 2019
Computers, Office Equipment, and Minor Computer Software [Member]
Property, Plant and Equipment [Line Items]
Estimated Useful Life (Years)	3 years
Computer Software [Member]
Property, Plant and Equipment [Line Items]
Estimated Useful Life (Years)	7 years
Manufacturing Equipment [Member] | Minimum [Member]
Property, Plant and Equipment [Line Items]
Estimated Useful Life (Years)	7 years
Manufacturing Equipment [Member] | Maximum [Member]
Property, Plant and Equipment [Line Items]
Estimated Useful Life (Years)	10 years
Furniture and Fixtures [Member]
Property, Plant and Equipment [Line Items]
Estimated Useful Life (Years)	5 years

Fair Value of Financial Asset_3

Fair Value of Financial Assets and Liabilities - Schedule of Assets Measured at Fair Value on Recurring Basis (Detail) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities	$ 87,991	$ 171,555
Fair Value Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	35,392	57,739
Marketable securities	87,991	171,555
Assets, Total	123,383	229,294
Fair Value Measurements, Recurring [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	35,392	57,739
Marketable securities	87,991	171,555
Assets, Total	$ 123,383	$ 229,294

Fair Value of Financial Asset_4

Fair Value of Financial Assets and Liabilities - Additional Information (Detail) - USD ($)	9 Months Ended
	Sep. 30, 2019	Aug. 02, 2019	Dec. 31, 2018	May 02, 2017
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Long-term debt, net	$ 40,070,000		$ 3,640,000
Silicon Valley Bank [Member] | 2019 Term Loan [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Term loan, principal amount		$ 40,000,000
Long-term debt, net		$ 40,000,000
Silicon Valley Bank And MidCap Financial Funding XIII Trust [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Repayments of Lines of Credit	$ 7,700,000
2024 Convertible Notes [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Term loan, principal amount				$ 201,300,000
Fair value of liability				136,700,000
Unamortized debt discount				$ 64,500,000
Debt instrument interest rate	3.375%			3.375%
Estimated fair value of Convertible Notes	$ 187,900,000

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, 2019	Dec. 31, 2018
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 87,860	$ 171,632
Gross Unrealized Gains	138	20
Gross Unrealized Losses	(7)	(97)
Fair Value	87,991	171,555
U.S. Government Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	39,837	39,910
Gross Unrealized Gains	48
Gross Unrealized Losses		(12)
Fair Value	39,885	39,898
Corporate Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	48,023	94,999
Gross Unrealized Gains	90	20
Gross Unrealized Losses	(7)	(85)
Fair Value	$ 48,106	94,934
Commercial Paper [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		36,723
Fair Value		$ 36,723

Marketable Securities - Additio

Marketable Securities - Additional Information (Detail) - USD ($)	Sep. 30, 2019	Dec. 31, 2018
Investments Debt And Equity Securities [Abstract]
Marketable securities	$ 87,991,000	$ 171,555,000
Long-term investment, marketable securities	$ 0	$ 0

Prepaid Expenses and Other Cu_3

Prepaid Expenses and Other Current Assets - Prepaid Expenses and Other Current Assets (Detail) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Deferred Costs Capitalized Prepaid And Other Assets Disclosure [Abstract]
Prepaid expenses	$ 4,759	$ 4,717
Deposits	61	66
Interest receivable on marketable securities	415	717
Total prepaid expenses and other current assets	$ 5,235	$ 5,500

Inventory - Schedule of Invento

Inventory - Schedule of Inventory (Detail) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Inventory Disclosure [Abstract]
Raw materials	$ 2,531	$ 2,367
Work in process	8,004	3,553
Finished goods	4,238	1,717
Total inventories	$ 14,773	$ 7,637

Inventory - Additional Informat

Inventory - Additional Information (Detail) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Inventory [Line Items]
Inventory finished goods shelf life			24 months
Write-downs to inventory			$ 0
Product [Member] | United Kingdom Facility at Patheon UK Limited [Member]
Inventory [Line Items]
Cost of sales expense for unabsorbed manufacturing and overhead costs	$ 900,000	$ 5,000,000	$ 900,000	$ 1,400,000

Property and Equipment, Net - C

Property and Equipment, Net - Components of Property and Equipment (Detail) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Property, Plant and Equipment [Line Items]
Property and equipment gross	$ 18,061	$ 16,402
Less: Accumulated depreciation	(7,410)	(5,692)
Total property and equipment, net	10,651	10,710
Computer and Office Equipment [Member]
Property, Plant and Equipment [Line Items]
Property and equipment gross	1,133	1,133
Manufacturing Equipment [Member]
Property, Plant and Equipment [Line Items]
Property and equipment gross	12,147	12,000
Furniture and Fixtures [Member]
Property, Plant and Equipment [Line Items]
Property and equipment gross	609	604
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Property and equipment gross	815	815
Construction in Progress [Member]
Property, Plant and Equipment [Line Items]
Property and equipment gross	2,902	1,416
Software [Member]
Property, Plant and Equipment [Line Items]
Property and equipment gross	$ 455	$ 434

Property and Equipment, Net - A

Property and Equipment, Net - Additional Information (Detail) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Property Plant And Equipment [Abstract]
Depreciation	$ 200,000	$ 400,000	$ 733,000	$ 1,494,000
Property and equipment disposals			$ 0

Accrued Expenses and Other Cu_3

Accrued Expenses and Other Current Liabilities - Schedule of Accrued Expenses and Other Current Liabilities (Detail) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Payables And Accruals [Abstract]
Research and development	$ 2,799	$ 1,216
Payroll and other employee-related expenses	10,635	8,207
Professional services fees	4,666	2,544
Accrued interest	3,052	1,195
Product revenue reserves	2,466	616
Accrual for employee stock purchase plan	591	251
Other	210	281
Total accrued expenses and other current liabilities	$ 24,419	$ 14,310

Debt - Additional Information (

Debt - Additional Information (Detail)	Aug. 02, 2019USD ($)	May 02, 2017USD ($)	Aug. 31, 2019USD ($)	Sep. 30, 2019USD ($)$ / shares	Jun. 30, 2019	Sep. 30, 2019USD ($)d$ / sharesshares	Dec. 31, 2018USD ($)	Aug. 04, 2015USD ($)
Debt Instrument [Line Items]
Debt extinguishment loss						$ (352,000)
Long-term debt, net				$ 40,070,000		$ 40,070,000	$ 3,640,000
Interest on final payment				4.75%		4.75%
Carrying value of term loan				$ 40,100,000		$ 40,100,000
Debt issuance costs						$ 161,000
Repaid In Year One [Member]
Debt Instrument [Line Items]
Debt instrument interest rate				3.00%		3.00%
Repaid In Year Two [Member]
Debt Instrument [Line Items]
Debt instrument interest rate				2.00%		2.00%
Repaid In Year Three [Member]
Debt Instrument [Line Items]
Debt instrument interest rate				1.00%		1.00%
Repaid In Year Four And Thereafter [Member]
Debt Instrument [Line Items]
Debt instrument interest rate				0.00%		0.00%
2015 Term Loan [Member]
Debt Instrument [Line Items]
Repayments of Lines of Credit						$ 7,700,000
Carrying value of term loan				$ 40,070,000		40,070,000
Liability component of Convertible Notes recorded as long-term debt				49,772,000		49,772,000
Mid Cap Financial Trust [Member] | 2015 Term Loan [Member]
Debt Instrument [Line Items]
Term loan, maximum borrowings								$ 30,000,000
Final payment of borrowed amount			$ 2,700,000
Debt extinguishment loss						$ 400,000
Silicon Valley Bank [Member] | Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Term loan, maximum borrowings	$ 20,000,000
Debt Instrument Maturity Date						Jan. 1, 2024
Debt Instrument Covenant Minimum Revenues						$ 80,000,000
Debt instrument interest rate description						Borrowings under the revolving credit facility accrue interest monthly at a floating interest rate equal to the greater of the prime rate or 5.50% per annum.
Unused portion of revolving line, percentage						0.25%
Revolver commitment amount				20,000,000		$ 20,000,000
Line of credit facility, fee description						unused revolving line facility fee equal to 0.25% per annum of the average unused portion of the revolving line.  multiplied by the difference between the total amount available to be borrowed (the “Revolver Commitment Amount”) of $20.0 million and the greater of the average outstanding revolver balance and 25% of the Commitment Amount
Line of credit facility, minimum interest calculation as a percentage of revolving commitment amount						25.00%
Revolving credit facility and any related fees, description						Beginning on January 1, 2020, if the interest payment on the revolving credit facility is less than the amount of interest that would have been payable had the Company borrowed 25% of the Revolver Commitment Amount, then the Company will be required to pay the difference.
Silicon Valley Bank [Member] | Revolving Credit Facility [Member] | Repaid In Year One [Member]
Debt Instrument [Line Items]
Line of credit facility, termination fees, percentage						2.00%
Silicon Valley Bank [Member] | Revolving Credit Facility [Member] | Repaid In Year Two [Member]
Debt Instrument [Line Items]
Line of credit facility, termination fees, percentage						1.00%
Silicon Valley Bank [Member] | Revolving Credit Facility [Member] | Repaid In Year Three And Thereafter [Member]
Debt Instrument [Line Items]
Line of credit facility, termination fees, percentage						0.00%
Silicon Valley Bank [Member] | Revolving Credit Facility [Member] | Maximum [Member]
Debt Instrument [Line Items]
Line of credit facility, collateral fees, amount						$ 10,000,000
Silicon Valley Bank [Member] | 2015 Term Loan [Member]
Debt Instrument [Line Items]
Long-term debt, net				$ 40,000,000		$ 40,000,000
Silicon Valley Bank [Member] | 2019 Term Loan [Member]
Debt Instrument [Line Items]
Term loan, principal amount	40,000,000
Debt Instrument Maturity Date						Jan. 1, 2024
Long-term debt, net	$ 40,000,000
Debt instrument interest rate description						Borrowings under the 2019 term loan accrue interest monthly at a floating interest rate equal to the greater of the prime rate plus 1.5% or 6.5% per annum
Term loan, first periodic payment date	Feb. 1, 2021
Interest on final payment	4.75%
Term loan, payment description						interest-only period of 18 months, principal is due in 36 equal monthly installments
Silicon Valley Bank [Member] | 2019 Term Loan [Member] | Interest-Only-Strip [Member]
Debt Instrument [Line Items]
Term loan, Interest payment period	18 months
Silicon Valley Bank [Member] | 2019 Term Loan [Member] | Principal-Only-Strip [Member]
Debt Instrument [Line Items]
Term loan, Interest payment period	36 months
2024 Convertible Notes [Member]
Debt Instrument [Line Items]
Term loan, principal amount		$ 201,300,000
Debt Instrument Maturity Date		May 1, 2024
Debt instrument interest rate		3.375%		3.375%		3.375%
Debt instrument interest rate		3.375%		9.71%		9.71%
Debt instrument frequency of periodic payment					semi-annually
Net proceeds from offering of convertible senior notes		$ 194,800,000
Debt discount and issuance costs		6,500,000		$ 68,900,000		$ 68,900,000
Number of shares issued upon conversion of $1,000 debt principal amount | shares						37.3413
Debt instrument convertible initial conversion price per share of common stock | $ / shares				$ 26.78		$ 26.78
Number of days within 30 consecutive trading days in which the closing price of the entity's common stock must exceed the conversion price for the notes to be convertible into common stock | d						20
Number of consecutive trading days during which the closing price of the entity's common stock must exceed the conversion price for at least 20 days in order for the notes to be convertible into common stock | d						30
Percentage of the closing sales price of the entity's common stock that the conversion price must exceed in order for the notes to be convertible						130.00%
Number of consecutive business days immediately after any five consecutive trading day period during the note measurement period | d						5
Number of consecutive trading days before five consecutive business days during the note measurement period | d						10
Liability component of Convertible Notes recorded as long-term debt		136,700,000
Equity component of Convertible Notes recorded as additional paid-in capital		$ 64,500,000
Debt instrument effective interest rate period						7 years
Debt issuance costs						$ 6,500,000
Debt issuance costs allocated to liability component						4,400,000
Debt issuance costs allocated to equity component reduction to additional paid-in capital						2,100,000
Interest expense				$ 3,700,000		11,000,000
Amortization of debt discount				$ 2,000,000		$ 5,900,000
2024 Convertible Notes [Member] | Repaid In Year Two [Member]
Debt Instrument [Line Items]
Number of days within 30 consecutive trading days in which the closing price of the entity's common stock must exceed the conversion price for the notes to be convertible into common stock | d						20
Number of consecutive trading days during which the closing price of the entity's common stock must exceed the conversion price for at least 20 days in order for the notes to be convertible into common stock | d						30
Percentage of the closing sales price of the entity's common stock that the conversion price must exceed in order for the notes to be convertible						130.00%
Debt instrument redemption date						May 6, 2020
Redemption price percentage of principal amount to be redeemed						100.00%
2024 Convertible Notes [Member] | Maximum [Member]
Debt Instrument [Line Items]
Debt instrument conversion obligation trading price as percentage of product common stock closing sale price and conversion rate						98.00%

Debt - Schedule of Annual Princ

Debt - Schedule of Annual Principal and Interest Payments Due Under Term Loan (Detail) $ in Thousands	Sep. 30, 2019USD ($)
Long-term Debt, Fiscal Year Maturity [Abstract]
Total	$ 40,100
2015 Term Loan [Member]
Long-term Debt, Fiscal Year Maturity [Abstract]
2019	679
2020	2,745
2021	14,611
2022	14,816
2023	13,903
Thereafter	3,018
Total	49,772
Less interest	(7,872)
Less unamortized portion of final payment	(1,830)
Total	$ 40,070

Debt - Summary of Carrying Valu

Debt - Summary of Carrying Value of Convertible Notes (Detail) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Debt Instrument [Line Items]
Amortization of debt discount and debt issuance costs	$ 6,505	$ 5,786
Carrying value 2024 Convertible Notes	151,204		$ 144,879
2024 Convertible Notes [Member]
Debt Instrument [Line Items]
Gross proceeds	201,250
Gross proceeds, Portion of proceeds allocated to equity component (additional paid-in capital)	(64,541)
Debt issuance costs	(6,470)
Debt issuance costs, Portion of issuance costs allocated to equity component (additional paid-in capital)	2,075
Amortization of debt discount and debt issuance costs	18,890
Carrying value 2024 Convertible Notes	$ 151,204

Stock-Based Compensation - Sche

Stock-Based Compensation - Schedule of Relevant Data Used to Estimate Fair Value of Stock Option Grants (Detail)	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Risk-free interest rates, Minimum	1.42%	2.82%	1.42%	2.67%
Risk-free interest rates, Maximum	1.90%	2.96%	2.67%	2.96%
Expected dividend yield	0.00%	0.00%	0.00%	0.00%
Expected term (in years)	7 years 2 months 12 days	6 years	6 years 2 months 12 days	6 years
Expected volatility, Minimum	67.10%	71.30%	67.10%	69.80%
Expected volatility, Maximum	67.50%	72.10%	69.50%	72.10%

Stock-Based Compensation - Summ

Stock-Based Compensation - Summary of Stock Option Activity (Detail)	9 Months Ended
	Sep. 30, 2019$ / sharesshares
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Shares Issuable Under Options, Beginning balance | shares	4,435,000
Shares Issuable Under Options, Granted | shares	999,000
Shares Issuable Under Options, Exercised | shares	(45,882)
Shares Issuable Under Options, Cancelled | shares	(522,000)
Shares Issuable Under Options, Ending balance | shares	4,865,658
Shares Issuable Under Options, Options vested and expected to vest at June 30, 2019 | shares	4,866,000
Shares Issuable Under Options, Options exercisable at June 30, 2019 | shares	2,905,000
Weighted Average Exercise Price Per Share, Beginning balance | $ / shares	$ 19.21
Weighted Average Exercise Price Per Share, Granted | $ / shares	13.45
Weighted Average Exercise Price Per Share, Exercised | $ / shares	0.19
Weighted Average Exercise Price Per Share, Cancelled | $ / shares	20.25
Weighted Average Exercise Price Per Share, Ending balance | $ / shares	18.10
Weighted Average Exercise Price Per Share, Options vested and expected to vest at June 30, 2019 | $ / shares	18.10
Weighted Average Exercise Price Per Share, Options exercisable at June 30, 2019 | $ / shares	$ 18.32

Stock-Based Compensation - Addi

Stock-Based Compensation - Additional Information (Detail)	Oct. 06, 2017USD ($)shares	Jan. 04, 2016shares	Dec. 31, 2017USD ($)	Jun. 30, 2019	Jun. 30, 2018	Sep. 30, 2019USD ($)Installment$ / sharesshares	Sep. 30, 2018$ / sharesshares	Dec. 31, 2018$ / sharesshares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of options exercised | shares						45,882
Aggregate intrinsic value of stock options exercised						$ 587,279
Options to purchase common stock, outstanding | shares						4,865,658	4,464,877	4,435,000
Weighted average remaining contractual term				7 years 3 months 18 days	7 years 8 months 12 days
Weighted average exercise price | $ / shares						$ 18.10	$ 19.24	$ 19.21
Weighted average grant date fair value of options granted | $ / shares						$ 8.55	$ 15.36
Unrecognized stock-based compensation expense						$ 21,100,000
Unrecognized compensation costs, weighted-average recognition periods						2 years 3 months 18 days
Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share based compensation, number of shares granted | shares	122,800	189,300				849,706
Grant date fair value of restricted common stock units under performance-based vesting	$ 2,200,000		$ 1,600,000
Unrecognized stock-based compensation expense						$ 11,600,000
Unrecognized compensation costs, weighted-average recognition periods						3 years 1 month 6 days
Weighted average grant date fair value, shares granted, per share | $ / shares						$ 14.49
Awards vesting right						The RSUs vest in four substantially equal installments on each of the first four anniversaries of the vesting commencement date, subject to the employee’s continued employment with, or services to, the Company on each vesting date.
Restricted Stock Units (RSUs) [Member] | First Anniversary [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share based compensation, award vesting installments | Installment						4
Restricted Stock Units (RSUs) [Member] | Second Anniversary [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share based compensation, award vesting installments | Installment						4
Restricted Stock Units (RSUs) [Member] | Third Anniversary [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share based compensation, award vesting installments | Installment						4
Restricted Stock Units (RSUs) [Member] | Fourth Anniversary [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share based compensation, award vesting installments | Installment						4
Restricted Stock Units (RSUs) [Member] | January 4, 2016 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized stock-based compensation expense						$ 600,000
Unrecognized compensation costs, weighted-average recognition periods						2 years

Stock-Based Compensation - Su_2

Stock-Based Compensation - Summary of of RSU Activity (Detail) - Restricted Stock Units (RSUs) [Member] - $ / shares	Oct. 06, 2017	Jan. 04, 2016	Sep. 30, 2019
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of Shares, Beginning balance			252,000
Number of Shares, Granted	122,800	189,300	849,706
Number of Shares, Vested/Released			(54,000)
Number of Shares, Cancelled			(142,000)
Number of Shares, Ending balance			906,000
Weighted Average Grant Date Fair Value Per Share, Beginning balance			$ 22.25
Weighted Average Grant Date Fair Value Per Share, Granted			14.49
Weighted Average Grant Date Fair Value Per Share, Vested/Released			22.96
Weighted Average Grant Date Fair Value Per Share, Cancelled			15.81
Weighted Average Grant Date Fair Value Per Share, Ending balance			$ 15.94

Stock-Based Compensation - Stoc

Stock-Based Compensation - Stock-Based Compensation Expense Related to Stock Options, and RSUs and Shares Purchased Under Employee Stock Purchase Plan (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	$ 4,025	$ 3,999	$ 12,095	$ 11,640
Research and Development [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	1,304	1,276	3,845	3,563
Selling, General and Administrative [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	$ 2,721	$ 2,723	$ 8,250	$ 8,077

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, shares in Thousands, $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Sep. 30, 2019	Sep. 30, 2018
Numerator:
Net loss	$ (38,232)	$ (36,487)	$ (41,538)	$ (43,640)	$ (43,875)	$ (41,569)	$ (116,257)	$ (129,084)
Net loss:	$ (38,232)	$ (36,487)	$ (41,538)	$ (43,640)	$ (43,875)	$ (41,569)	$ (116,257)	$ (129,084)
Denominator:
Weighted average common shares outstanding, basic and diluted	38,125			37,818			38,043	37,712
Net loss per share, basic and diluted	$ (1)			$ (1.15)			$ (3.06)	$ (3.42)

Net Loss per Share - Schedule_2

Net Loss per Share - Schedule of Common Stock Equivalents Excluded from Calculation of Diluted Net Loss Per Share, as Including them Would have Anti-dilutive Effect (Detail) - shares	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Common stock equivalents excluded from calculation of diluted net loss per share, as including them would have anti-dilutive effect	13,580	12,465	13,313	12,250
Shares Issuable Upon Conversion of the 2024 Convertible Notes [Member]
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Common stock equivalents excluded from calculation of diluted net loss per share, as including them would have anti-dilutive effect	7,515	7,515	7,515	7,515
Stock Options [Member]
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Common stock equivalents excluded from calculation of diluted net loss per share, as including them would have anti-dilutive effect	5,157	4,653	5,016	4,466
Restricted Stock Units [Member]
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Common stock equivalents excluded from calculation of diluted net loss per share, as including them would have anti-dilutive effect	908	297	782	269

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Detail)

Oct. 24, 2018USD ($)

Sep. 30, 2019USD ($)ft²

Jun. 30, 2019USD ($)ft²

Dec. 31, 2017USD ($)

Feb. 28, 2017USD ($)

Nov. 30, 2016Term

Jul. 31, 2015

May 31, 2013ft²

Sep. 30, 2019USD ($)ft²

Sep. 30, 2019USD ($)ft²

Jan. 01, 2019USD ($)

Dec. 31, 2018

Commitment And Contingencies [Line Items]

Right-of-use assets

$ 8,618,000

$ 8,618,000

$ 8,618,000

$ 6,600,000

Operating lease liabilities

$ 7,000,000

Operating lease, straight-line cost

$ 567,000

1,398,000

GeneQuine Biotherapeutics GmbH ("GeneQuine") [Member] | Definitive Agreement [Member]

Commitment And Contingencies [Line Items]

License agreement, upfront fee paid

$ 2,000,000

Milestone, Revenue recognized

0

Research and development milestone payment

$ 750,000

GeneQuine Biotherapeutics GmbH ("GeneQuine") [Member] | Definitive Agreement [Member] | Investigational New Drug (IND) [Member]

Commitment And Contingencies [Line Items]

Research and development milestone payment

750,000

GeneQuine Biotherapeutics GmbH ("GeneQuine") [Member] | Definitive Agreement [Member] | Maximum [Member]

Commitment And Contingencies [Line Items]

Additional milestone payments

54,000,000

Xenon Pharmaceuticals, Inc. ("Xenon") [Member] | Definitive Agreement [Member]

Commitment And Contingencies [Line Items]

License agreement, upfront fee paid

3,000,000

Milestone, Revenue recognized

$ 0

Xenon Pharmaceuticals, Inc. ("Xenon") [Member] | Definitive Agreement [Member] | Sales Related Milestone Payments [Member]

Commitment And Contingencies [Line Items]

Additional milestone payments

75,000,000

Xenon Pharmaceuticals, Inc. ("Xenon") [Member] | Definitive Agreement [Member] | Maximum [Member]

Commitment And Contingencies [Line Items]

Additional milestone payments

$ 40,800,000

Evonik Corporation [Member]

Commitment And Contingencies [Line Items]

Supply agreement period

5 years

Supply agreement renewal term

2 years

Number of renewal terms | Term

2

Supply agreement description

The Supply Agreement will renew for two successive two year terms upon mutual written consent by both parties.

Manufacturing and Supply Agreement with Patheon UK Limited [Member]

Commitment And Contingencies [Line Items]

Operating lease, discount rate

6.10%

Operating lease, remaining lease term

8 years 1 month 6 days

8 years 1 month 6 days

8 years 1 month 6 days

Operating lease, straight-line cost

$ 54,000

$ 147,000

Manufacturing agreement period

10 years

Increase in operating lease liability

$ 500,000

Increase in right of use asset

$ 500,000

Phase 2 Proof of Concept (PoC) Clinical Trial [Member] | GeneQuine Biotherapeutics GmbH ("GeneQuine") [Member] | Definitive Agreement [Member] | Maximum [Member]

Commitment And Contingencies [Line Items]

Additional milestone payments

$ 8,700,000

Phase 2 Proof of Concept (PoC) Clinical Trial [Member] | Xenon Pharmaceuticals, Inc. ("Xenon") [Member] | Definitive Agreement [Member] | Maximum [Member]

Commitment And Contingencies [Line Items]

Additional milestone payments

$ 9,000,000

Burlington Massachusetts [Member]

Commitment And Contingencies [Line Items]

Operating lease office space | ft²

41,873

36,500

41,873

41,873

Lease termination date

Oct. 31, 2023

Apr. 30, 2025

Operating lease, discount rate

6.80%

6.80%

6.80%

8.90%

Operating lease, remaining lease term

5 years 7 months 6 days

5 years 7 months 6 days

5 years 7 months 6 days

4 years 9 months 18 days

Additional leased office space | ft²

5,330

Minimum monthly lease payments

$ 108,000

Lease commencement date for additional space

Jul. 1, 2019

Right-of-use assets

$ 2,500

$ 2,500

$ 2,500

Operating lease liabilities

$ 2,500

2,500

2,500

Operating lease, straight-line cost

$ 500,000

$ 1,100,000

Lessee, operating lease, extension term

18 months

18 months

18 months

Woburn, Massachusetts [Member]

Commitment And Contingencies [Line Items]

Operating lease, discount rate

8.40%

Operating lease, remaining lease term

2 years 4 months 24 days

2 years 4 months 24 days

2 years 4 months 24 days

3 years 2 months 12 days

Operating lease, straight-line cost

$ 46,000

$ 139,000

Operating lease term

5 years

Monthly lease payment

$ 15,000

Operating lease, option to extend

The Woburn lease includes an option to extend the term of the lease for two years.

Commitments and Contingencies_2

Commitments and Contingencies - Components of Lease Expense and Related Cash Flows (Detail) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2019
Commitment And Contingencies [Line Items]
Total operating lease cost	$ 567	$ 1,398
Operating cash flows from operating leases	686	1,781
Inventory [Member]
Commitment And Contingencies [Line Items]
Total operating lease cost	54	147
Operating Expense [Member]
Commitment And Contingencies [Line Items]
Total operating lease cost	$ 513	$ 1,251

Commitments and Contingencies_3

Commitments and Contingencies - Schedule of Maturities of Lease Liability Due Under Lease Agreements (Detail) $ in Thousands	Sep. 30, 2019USD ($)
Commitments And Contingencies Disclosure [Abstract]
Operating Lease Obligations, 2019	$ 470
Operating Lease Obligations, 2020	1,968
Operating Lease Obligations, 2021	2,016
Operating Lease Obligations, 2022	1,863
Operating Lease Obligations, 2023	1,871
Operating Lease Obligation, Thereafter	3,087
Operating Lease Obligation,Present value of imputed interest	(2,530)
Operating Lease Obligation, Total	$ 8,745

Commitments and Contingencies_4

Commitments and Contingencies - Future Minimum Lease Payments under Operating Leases (Detail) $ in Thousands	Dec. 31, 2018USD ($)
Commitments And Contingencies Disclosure [Abstract]
2019	$ 1,491
2020	1,533
2021	1,576
2022	1,447
2023	1,203
Total	$ 7,250

Commitments and Contingencies_5

Commitments and Contingencies - Schedule of Future Minimum Payments under Manufacturing Agreement with Patheon (Detail) - Manufacturing and Supply Agreement with Patheon UK Limited [Member] $ in Thousands	Dec. 31, 2018USD ($)
Property Subject To Or Available For Operating Lease [Line Items]
2019	$ 8,027
2020	8,027
2021	8,027
2022	8,027
2023	8,027
2024 and thereafter	30,102
Total	$ 70,237