Enanta Pharmaceuticals (ENTA) 10-K 24 Nov 21 2021 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($)	12 Months Ended
	Sep. 30, 2021	Nov. 01, 2021	Mar. 31, 2021
Cover [Abstract]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Sep. 30, 2021
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	FY
Trading Symbol	ENTA
Entity Registrant Name	ENANTA PHARMACEUTICALS, INC
Entity Central Index Key	0001177648
Current Fiscal Year End Date	--09-30
Entity Well-known Seasoned Issuer	Yes
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
ICFR Auditor Attestation Flag	true
Entity Common Stock, Shares Outstanding		20,324,795
Entity Public Float			$ 864,668,968
Title of 12(b) Security	Common Stock, par value $0.01 per share
Security Exchange Name	NASDAQ
Entity File Number	001-35839
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	04-3205099
Entity Address, Address Line One	500 Arsenal Street
Entity Address, City or Town	Watertown
Entity Address, State or Province	MA
Entity Address, Postal Zip Code	02472
City Area Code	617
Local Phone Number	607-0800
Document Annual Report	true
Document Transition Report	false
Documents Incorporated by Reference	Portions of the registrant’s Definitive Proxy Statement for its 2022 Annual Meeting of Stockholders scheduled to be held on March 3, 2022, which Definitive Proxy will be filed with the Securities and Exchange Commission not later than 120 days after the registrant’s fiscal year end of September 30, 2021 are incorporated by reference into Part III of this Form 10-K.

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Sep. 30, 2021	Sep. 30, 2020
Current assets:
Cash and cash equivalents	$ 57,206	$ 87,131
Short-term marketable securities	186,796	299,518
Accounts receivable	23,576	23,492
Prepaid expenses and other current assets	14,188	13,655
Income tax receivable	37,255	13,041
Total current assets	319,021	436,837
Long-term marketable securities	108,416	32,634
Property and equipment, net	5,943	8,596
Deferred tax assets		345
Operating lease, right-of-use assets	4,711	7,020
Restricted cash	608	608
Other long-term assets	92	92
Total assets	438,791	486,132
Current liabilities:
Accounts payable	9,540	5,737
Accrued expenses and other current liabilities	22,429	14,159
Operating lease liabilities	4,203	4,261
Total current liabilities	36,172	24,157
Operating lease liabilities, net of current portion	1,126	3,838
Series 1 nonconvertible preferred stock	1,506	1,479
Other long-term liabilities	558	1,078
Total liabilities	39,362	30,552
Commitments and contingencies (Note 13)
Stockholders' equity:
Common stock; $0.01 par value per share, 100,000 shares authorized; 20,238 and 20,077 shares issued and outstanding at September 30, 2021 and September 30, 2020, respectively	202	201
Additional paid-in capital	351,033	326,963
Accumulated other comprehensive income (loss)	(382)	844
Retained earnings	48,576	127,572
Total stockholders' equity	399,429	455,580
Total liabilities and stockholders' equity	$ 438,791	$ 486,132

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - $ / shares shares in Thousands	Sep. 30, 2021	Sep. 30, 2020
Statement Of Financial Position [Abstract]
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	100,000	100,000
Common stock, shares issued	20,238	20,077
Common stock, shares outstanding	20,238	20,077

Consolidated Statements of Oper

Consolidated Statements of Operations - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019
Revenue
Total revenue	$ 97,074	$ 122,473	$ 205,197
Operating expenses:
Research and development	174,111	136,756	142,213
General and administrative	32,536	27,356	26,246
Total operating expenses	206,647	164,112	168,459
Income (loss) from operations	(109,573)	(41,639)	36,738
Other income (expense), net:
Interest and investment income, net	2,021	6,471	8,819
Change in fair value of Series 1 nonconvertible preferred stock	(27)	149
Total other income (expense), net	1,994	6,620	8,819
Income (loss) before income taxes	(107,579)	(35,019)	45,557
Income tax (expense) benefit	28,583	(1,149)	826
Net income (loss)	$ (78,996)	$ (36,168)	$ 46,383
Net income (loss) per share:
Basic	$ (3.92)	$ (1.81)	$ 2.37
Diluted	$ (3.92)	$ (1.81)	$ 2.21
Weighted average shares outstanding:
Basic	20,171	19,940	19,584
Diluted	20,171	19,940	20,968
Royalty [Member]
Revenue
Total revenue	$ 97,074	$ 122,473	$ 205,197

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Income (Loss) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019
Statement Of Income And Comprehensive Income [Abstract]
Net income (loss)	$ (78,996)	$ (36,168)	$ 46,383
Other comprehensive income (loss):
Net unrealized gain (loss) on marketable securities, net of tax expense (benefit) of $0, $388, and $173	(1,226)	698	544
Total other comprehensive income (loss), net of tax	(1,226)	698	544
Comprehensive income (loss)	$ (80,222)	$ (35,470)	$ 46,927

Consolidated Statements of Co_2

Consolidated Statements of Comprehensive Income (Loss) (Parenthetical) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019
Statement Of Income And Comprehensive Income [Abstract]
Net unrealized gain (loss) on marketable securities, tax	$ 0	$ 388	$ 173

Consolidated Statements of Stoc

Consolidated Statements of Stockholders' Equity - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock [Member]	Additional Paid-In Capital [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Retained Earnings [Member]
Beginning Balance at Sep. 30, 2018	$ 393,679	$ 194	$ 276,526	$ (398)	$ 117,357
Beginning Balance, Shares at Sep. 30, 2018		19,395
Exercise of stock options and warrants	6,848	$ 2	6,846
Exercise of stock options and warrants, Shares		231
Vesting of restricted stock units, net of withholding	(4,188)	$ 1	(4,189)
Vesting of restricted stock units, net of withholding, Shares		77
Stock-based compensation expense	19,226		19,226
Total other comprehensive income (loss), net of tax	544			544
Net income (loss)	46,383				46,383
Ending Balance at Sep. 30, 2019	462,492	$ 197	298,409	146	163,740
Ending Balance, Shares at Sep. 30, 2019		19,703
Exercise of stock options	10,481	$ 4	10,477
Exercise of stock options, Shares		327
Vesting of restricted stock units, net of withholding	(1,498)		(1,498)
Vesting of restricted stock units, net of withholding, Shares		47
Stock-based compensation expense	19,575		19,575
Total other comprehensive income (loss), net of tax	698			698
Net income (loss)	(36,168)				(36,168)
Ending Balance at Sep. 30, 2020	455,580	$ 201	326,963	844	127,572
Ending Balance, Shares at Sep. 30, 2020		20,077
Exercise of stock options	$ 3,614	$ 1	3,613
Exercise of stock options, Shares	129	129
Vesting of restricted stock units, net of withholding	$ (534)		(534)
Vesting of restricted stock units, net of withholding, Shares		32
Stock-based compensation expense	20,991		20,991
Total other comprehensive income (loss), net of tax	(1,226)			(1,226)
Net income (loss)	(78,996)				(78,996)
Ending Balance at Sep. 30, 2021	$ 399,429	$ 202	$ 351,033	$ (382)	$ 48,576
Ending Balance, Shares at Sep. 30, 2021		20,238

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019
Cash flows from operating activities
Net income (loss)	$ (78,996)	$ (36,168)	$ 46,383
Adjustments to reconcile net income to net cash provided by operating activities:
Stock-based compensation expense	20,991	19,575	19,226
Depreciation and amortization expense	3,334	3,644	3,258
Deferred income taxes	345	10,608	(3,138)
Premium paid on marketable securities	(4,028)	(3,575)	(1,491)
(Accretion) amortization of (discount) premium on marketable securities	2,116	304	(4,336)
Change in fair value of warrant liability and Series 1 nonconvertible preferred stock	27	(149)
Other non-cash items	(97)	(51)	25
Change in operating assets and liabilities:
Accounts receivable	(84)	27,821	15,892
Prepaid expenses and other current assets	(533)	(7,270)	(1,929)
Income tax receivable	(24,214)	(4,127)	(8,916)
Operating lease, right-of-use assets	5,418	3,184
Accounts payable	3,774	(883)	1,791
Accrued expenses	8,350	(1,368)	5,750
Income taxes payable			(1,388)
Operating lease liabilities	(5,879)	(3,535)
Other long-term liabilities	(520)	(922)	291
Net cash provided by (used in) operating activities	(69,996)	7,088	71,418
Cash flows from investing activities
Purchase of marketable securities	(307,348)	(338,553)	(549,312)
Proceeds from maturities and sale of marketable securities	345,089	359,828	468,065
Purchase of property and equipment	(750)	(1,445)	(5,417)
Net cash provided by (used in) investing activities	36,991	19,830	(86,664)
Cash flows from financing activities
Proceeds from exercise of stock options and warrants	3,614	10,481	6,848
Payments for settlement of share-based awards	(534)	(1,498)	(4,188)
Payments of capital lease obligations			(86)
Net cash provided by financing activities	3,080	8,983	2,574
Net increase (decrease) in cash and cash equivalents	(29,925)	35,901	(12,672)
Cash, cash equivalents and restricted cash at beginning of period	87,739	51,838	64,510
Cash, cash equivalents and restricted cash at end of period	57,814	87,739	51,838
Supplemental disclosure of cash flow information:
Cash paid for income taxes	32	105	12,672
Non-cash items:
Purchases of fixed assets included in accounts payable and accrued expenses	137	188	$ 320
Operating lease liabilities arising from obtaining right-of-use assets	$ 3,320	$ 3,053

Nature of the Business

Nature of the Business	12 Months Ended
	Sep. 30, 2021
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Nature of the Business	1. Nature of the Business Enanta Pharmaceuticals, Inc. (the “Company”), incorporated in Delaware in 1995 , is a biotechnology company that uses its robust, chemistry-driven approach and drug discovery capabilities to become a leader in the discovery and development of small molecule drugs for the treatment of viral infections and liver diseases. The Company discovered glecaprevir, the second of two protease inhibitors discovered and developed through its collaboration with AbbVie for the treatment of chronic hepatitis C virus, or HCV. Glecaprevir is co-formulated as part of AbbVie’s leading direct-acting antiviral, or DAA, combination treatment for HCV, which is marketed under the tradenames MAVYRET ® (U.S.) and MAVIRET ® (ex-U.S.) (glecaprevir/pibrentasvir). Royalties from the Company’s AbbVie collaboration and its existing financial resources provide funding to support the Company’s wholly-owned research and development programs , which are primarily focused on the following disease targets: respiratory syncytial virus (“RSV”), hepatitis B virus (“HBV”), SARS-CoV-2, and human metapneumovirus (“hMPV”). The Company is subject to many of the risks common to companies in the biotechnology industry, including but not limited to, the uncertainties of research and development, competition from technological innovations of others, dependence on collaborative arrangements, protection of proprietary technology, dependence on key personnel and compliance with government regulation. Product candidates currently under development will require significant additional research and development efforts, including extensive preclinical and clinical testing and regulatory approvals, prior to commercialization. These efforts require significant amounts of capital, adequate personnel and infrastructure, and extensive compliance reporting capabilities. COVID-19 In March 2020, the World Health Organization declared COVID-19 a global pandemic and countries worldwide implemented various measures to contain the spread of the virus. National, state and local governments in affected regions have implemented and may continue to implement safety precautions, including quarantines, border closures, increased border controls, travel restrictions, shelter-in-place orders and shutdowns, business closures, cancellations of public gatherings and other measures. The extent and severity of the impact on the Company’s business and clinical trials will be determined largely by the extent to which there are disruptions in the supply chains for its research and product candidates, delays in the conduct of ongoing and future clinical trials, or reductions in the number of patients accessing AbbVie’s HCV regimens, or any combination of those events. During the second half of fiscal 2020 and through 2021, AbbVie experienced a decline in HCV sales compared to prior years as a result of a decline in patients accessing AbbVie’s HCV regimens due to the COVID-19 pandemic. This resulted in a decline in the Company’s royalty revenue earned for the years ended September 30, 2021 and 2020. The full extent to which the COVID-19 pandemic will directly or indirectly impact the Company’s business, results of operations and financial condition will depend on future developments that are highly uncertain and cannot be accurately predicted, including new information that may emerge concerning COVID-19 and public health actions taken to contain it, as well as the cumulative economic impact of both of those factors.

Summary of Significant Accounti

Summary of Significant Accounting Policies	12 Months Ended
	Sep. 30, 2021
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	2. Summary of Significant Accounting Policies Basis of Presentation The accompanying consolidated financial statements include those of the Company and its subsidiary, Enanta Pharmaceuticals Security Corporation, after elimination of all intercompany accounts and transactions. The accompanying consolidated financial statements have been prepared in conformity with accounting principles generally accepted in the United States of America (“GAAP”). Use of Estimates The preparation of consolidated financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, the disclosure of contingent assets and liabilities at the date of the consolidated financial statements, and the reported amounts of revenues and expenses during the reporting period. Significant estimates and assumptions reflected in these consolidated financial statements include, but are not limited to, management’s judgments with respect to its revenue arrangements; valuation of stock-based awards and the accrual of research and development expenses. Estimates are periodically reviewed in light of changes in circumstances, facts and experience. The future developments of the COVID-19 pandemic also may directly or indirectly impact the Company’s business. The Company has made estimates of the impact of COVID-19 in the Company’s consolidated financial statements as of September 30, 2021 . Actual results could differ from the Company’s estimates. Cash Equivalents and Marketable Securities The Company considers all short-term, highly liquid investments with original maturities of ninety days or less at acquisition date to be cash equivalents. Marketable securities with original maturities of greater than ninety days and remaining maturities of less than one year from the balance sheet date are classified as short-term marketable securities. Marketable securities with remaining maturities of greater than one year from the balance sheet date are classified as long-term marketable securities. The Company classifies all of its marketable securities as available-for-sale. The Company continually evaluates the credit ratings of its investment portfolio and underlying securities. The Company invests in accordance with its investment policy and invests at the date of purchase in securities with a rating of A3/A- or higher according to Moody’s or S&P or A- by Fitch. The Company reports available-for-sale investments at fair value as of each balance sheet date and records any unrealized gains or losses as a component of stockholders’ equity. The cost of securities sold is determined on a specific identification basis, and realized gains and losses are included in other income (expense), net within the consolidated statements of operations. When the fair value is below the amortized cost of a marketable security, an estimate of expected credit losses is made. The credit-related impairment amount is recognized in the consolidated statements of operations. Credit losses are recognized through the use of an allowance for credit losses account in the consolidated balance sheet and subsequent improvements in expected credit losses are recognized as a reversal of an amount in the allowance account. If the Company has the intent to sell the security or it is more likely than not that the Company will be required to sell the security prior to recovery of its amortized cost basis, then the allowance for the credit loss is written-off and the excess of the amortized cost basis of the asset over its fair value is recorded in the consolidated statements of operations. There were no credit losses recorded during the years ended September 30, 2021, 2020, and 2019 . Restricted Cash As of September 30, 2021 and 2020 the Company had an outstanding letter of credit collateralized by a money market account of $ 608 to the benefit of the landlord of one of the Company’s existing building leases. This amount was classified as long-term restricted cash as of September 30, 2021 and 2020 . Concentration of Credit Risk and of Significant Customers and Suppliers Financial instruments that potentially expose the Company to concentrations of credit risk consist primarily of cash, cash equivalents, marketable securities and accounts receivable. The Company has all cash and investment balances at one accredited financial institution, including cash in amounts that exceed federally insured limits. The Company does not believe that it is subject to unusual credit risk beyond the normal credit risk associated with commercial banking relationships. The Company has historically generated the majority of its revenue from its collaborative research and license agreements. As of September 30, 2021 and 2020, accounts receivable consisted of amounts due from the Company’s principal collaborator (see Note 7). The Company is completely dependent on third-party manufacturers for product supply for preclinical and clinical research activities. The Company relies and expects to continue to rely exclusively on several manufacturers to supply the Company with its drug supply requirements related to these activities. These research programs would be adversely affected by a significant interruption in the supply from these third-party manufacturers. Fair Value Measurements Certain assets and liabilities are carried at fair value under GAAP. Fair value is defined as the exchange price that would be received for an asset or paid to transfer a liability (an exit price) in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants on the measurement date. Valuation techniques used to measure fair value must maximize the use of observable inputs and minimize the use of unobservable inputs. A fair value hierarchy is based on three levels of inputs which are used to measure fair value, of which the first two levels are considered observable and the last is considered unobservable:  Level 1—Quoted prices in active markets for identical assets or liabilities.  Level 2—Observable inputs (other than Level 1 quoted prices) such as quoted prices in active markets for similar assets or liabilities, quoted prices in markets that are not active for identical or similar assets or liabilities, or other inputs that are observable or can be corroborated by observable market data.  Level 3—Unobservable inputs that are supported by little or no market activity and that are significant to determining the fair value of the assets or liabilities, including pricing models, discounted cash flow methodologies and similar techniques. The Company’s instruments that are carried at fair value are cash equivalents, marketable securities and the Series 1 nonconvertible preferred stock. The carrying values of accounts receivable, prepaid and other assets, accounts payable and accrued expenses approximate their fair value due to the short-term nature of these assets and liabilities. Property and Equipment Property and equipment are stated at cost less accumulated depreciation. Depreciation expense is recognized using the straight-line method over the following estimated useful lives: Laboratory and office equipment 5 years Leasehold improvements Shorter of life of lease or estimated useful life Purchased software 3 years Computer equipment 3 years Furniture 7 years Expenditures for repairs and maintenance of assets are charged to expense as incurred. Costs of major additions and betterments are capitalized and depreciated on a straight-line basis over their useful lives. Upon retirement or sale, the cost and related accumulated depreciation of assets disposed are removed from the accounts and any resulting gain or loss is included in income from operations in the consolidated statements of operations. Impairment of Long-Lived Assets The Company reviews long-lived assets, primarily property and equipment, for impairment whenever events or changes in business circumstances indicate that the carrying amount of the assets may not be fully recoverable. Factors that the Company considers in deciding when to perform an impairment review include significant underperformance of the business in relation to expectations, significant negative industry or economic trends, and significant changes or planned changes in the use of the assets. If an impairment review is performed to evaluate a long-lived asset for recoverability, the Company compares forecasts of undiscounted cash flows expected to result from the use and eventual disposition of the long-lived asset to its carrying value. An impairment loss would be recognized when estimated undiscounted future cash flows expected to result from the use of an asset are less than its carrying amount. The impairment loss would be based on the excess of the carrying value of the impaired asset over its fair value, determined based on discounted cash flows. To date, the Company has not recorded any impairment losses on long-lived assets. Revenue Recognition The Company’s revenue has been generated primarily through collaborative research and license agreements. The terms of these agreements contain multiple deliverables, which may include (i) licenses, (ii) research and development activities, and (iii) participation in joint research and development steering committees. The terms of these agreements may include nonrefundable upfront license fees, payments for research and development activities, payments based upon the achievement of certain milestones, and royalty payments based on product sales derived from the collaboration. The Company recognizes revenue to depict the transfer of promised goods or services to customers in an amount that reflects the consideration to which the Company expects to be entitled in exchange for those goods or services. The Company receives sales-based royalties for which the license is deemed to be the predominant item to which the royalties relate and thus the Company recognizes sales-based royalties as the underlying sales are earned. Research and Development Costs Included in research and development costs are wages, stock-based compensation and benefits of employees performing research and development, third-party license fees and other operational costs related to the Company’s research and development activities, including facility-related expenses and external costs of outside contractors engaged to conduct both preclinical and clinical studies and manufacture quantities of product for preclinical and clinical studies. The Company expenses the cost of each contract as the work is performed. Upfront payments and milestone payments made for the licensing of technology are expensed as research and development in the period in which they are incurred. Advance payments for goods or services to be received in the future for use in research and development activities are recorded as prepaid expenses. The prepaid amounts are expensed as the related goods are delivered or the services are performed. Research and Development and Pharmaceutical Drug Manufacturing Accruals The Company has entered into various contracts with third parties to perform research and development and pharmaceutical drug manufacturing. This includes contracts with contract research organizations (“CROs”), clinical manufacturing organizations (“CMOs”), testing laboratories, research hospitals and not for profit organizations and other entities to support our research and development activities. When billing terms under these contracts do not coincide with the timing of when the work is performed, the Company is required to make estimates of outstanding obligations as of period end to those third parties. The accrual estimates are based on a number of factors, including the Company’s knowledge of the research and development programs and pharmaceutical drug manufacturing activities and associated timelines, invoicing to date, and the provisions in the contract. Significant judgments and estimates are made in determining the accrued balances at the end of any reporting period. Actual results could differ from our estimates. Patent Costs All patent-related costs incurred in connection with filing and prosecuting patent applications are recorded as general and administrative expenses as incurred. Stock-Based Compensation The Company measures all stock options and other stock-based awards granted to employees at fair value on the date of grant. The Company uses the Black-Scholes option-pricing model in the valuation of its stock options. The fair value of performance-based awards and restricted stock units is based on the fair value of the stock on the date of grant. The Company uses the Monte-Carlo model in order to calculate the fair value of the market-based awards. The fair value of options is recognized as stock-based compensation expense over the requisite service period, which is generally the vesting period of the respective award. The Company accounts for stock-based compensation expense related to forfeitures as the forfeitures occur. For awards with graded vesting, the straight-line method of expense recognition is applied to all awards with service-only based conditions. The Company records stock-based compensation expense related to performance-based awards when the performance-based targets are probable of being achieved. The Company classifies stock-based compensation expense in the consolidated statements of operations in the same manner in which the award recipient’s payroll costs are classified. Income Taxes The Company accounts for income taxes using the asset and liability method, which requires the recognition of deferred tax assets and liabilities for the expected future tax consequences of events that have been recognized in the financial statements or in the Company’s tax returns. Deferred taxes are determined based on the difference between the financial reporting and tax basis of assets and liabilities using enacted tax rates in effect in the years in which the differences are expected to reverse. Changes in deferred tax assets and liabilities are recorded in income tax expense. The Company assesses the likelihood that its deferred tax assets will be recovered from future taxable income and, to the extent it believes based upon the weight of available evidence, that it is more likely than not that all or a portion of deferred tax assets will not be realized, a valuation allowance is established through a charge to income tax expense. The realization of deferred tax assets is dependent upon the Company’s ability to generate future taxable income during the periods in which those temporary differences become deductible. Potential for recovery of deferred tax assets is evaluated by estimating the future taxable profits expected and considering prudent and feasible tax planning strategies. Uncertain tax positions represent tax positions for which reserves have been established. The Company accounts for uncertainty in income taxes recognized in the consolidated financial statements by applying a two-step process to determine the amount to be recognized. First, the tax position must be evaluated to determine the likelihood that it will be sustained upon external examination by the taxing authorities. If the tax position is deemed more likely than not to be sustained, the tax position is then assessed to determine the amount of benefit to be recognized in the financial statements. The amount that may be recognized is the largest amount that has a greater than 50 % likelihood of being realized upon ultimate settlement. Income tax expense includes the effects of any resulting tax reserves, or unrecognized tax benefits, that are considered appropriate as well as the related net interest and penalties. Net Income (Loss) per Share Basic net income (loss) per common share is computed by dividing the net income by the weighted average number of shares of common stock outstanding for the period. Diluted net income per common share is computed by dividing net income by the weighted average number of common shares outstanding for the period, including potential dilutive common shares assuming the dilutive effect of outstanding stock options and unvested restricted stock units. Market-based awards are included in diluted net income per common share to the extent they would have vested if the period end date was the market criteria measurement date. In the event the Company reports a net loss for the period, the dilutive effect of options or awards is considered anti-dilutive and disclosed accordingly. Segment Data The Company manages its operations as a single segment for the purposes of assessing performance and making operating decisions. The Company is a biotechnology company focused on discovering and developing small molecule drugs for the treatment of viral infections and liver diseases. Revenue is generated exclusively from transactions occurring with partners located in the United States and all assets are held in the United States. Comprehensive Income (Loss) Comprehensive income (loss) includes net income (loss) as well as other changes in stockholders’ equity that result from transactions and economic events other than those with stockholders. The Company’s only element of other comprehensive income (loss) is unrealized gains and losses on available-for-sale marketable securities. Going Concern In August 2014, the Financial Accounting Standards Board (the “FASB”) issued ASU 2014-15, Presentation of Financial Statements - Going Concern (Subtopic 205-40) (“ASU 2014-15”). The Company adopted this standard as of September 30, 2017. The standard requires the Company to assess its ability to continue as a going concern one year beyond the date of filing and, in certain circumstances, provide additional footnote disclosures. Based on a detailed cash forecast incorporating current research and development activities and related spending plans, the Company believes that its current cash, cash equivalents and short-term and long-term marketable securities on hand at September 30, 2021 is sufficient to fund operations for at least the next twelve months beyond the date of issuance of these consolidated financial statements. The amount of capital available will depend on the Company’s management of its existing cash, cash equivalents and short-term and long-term marketable securities, as well as the level of future royalties the Company earns under its agreement with AbbVie. If the Company should require financing beyond these resources to fund its research and development efforts, it may not be able to obtain financing on acceptable terms, or at all. Recently Issued Accounting Pronouncements In June 2016, the FASB issued ASU No. 2016-13, Financial Instruments—Credit Losses (Topic 326) (“ASU 2016-13”), which introduces a new methodology for accounting for credit losses on financial instruments, including available-for-sale debt securities. The guidance establishes a new “expected loss model” that requires entities to estimate current expected credit losses on financial instruments by using all practical and relevant information. Any expected credit losses are to be reflected as allowances rather than reductions in the amortized cost of available-for-sale debt securities. The Company adopted ASU 2016-13 as of October 1, 2020. For available-for-sale debt securities with unrealized losses, the Company measures credit losses in a manner similar to previous U.S. GAAP, except that losses will be recognized as allowances instead of reductions in the amortized cost of the debt securities. The adoption of ASU 2016-13 did not have a material impact on the consolidated financial statements. The Company adopted ASU No. 2016-02, Leases (Topic 842) , as of October 1, 2019, using the modified retrospective method under ASU No. 2018-11, Leases (Topic 842): Targeted Improvements . The transition method allows entities to apply the transition requirements at the effective date rather than at the beginning of the earliest comparative period presented. The Company’s reporting for comparative periods is presented in accordance with ASC 840, Leases. Adoption of the new standard resulted in the recording of right of use (“ROU”) assets and lease liabilities of $ 7,151 and $ 8,622 , respectively. The adoption of the standard did not have a material impact on the Company’s results of operations or cash flows. The Company elected to use the transition package of three practical expedients, which among other things, allowed the Company to carry forward the historical lease classification. The Company has elected, under Topic 842, the further practical expedient not to separate non-lease components from the lease components to which they relate and instead to combine them and account for them as a single lease component. The Company also elected the accounting policy election to keep leases with a term of twelve months or less off the balance sheet and to recognize payments for those leases on a straight-line basis over the lease term. ROU assets represent the Company’s right to use an underlying asset for the lease term, and lease liabilities represent the Company’s obligation to make lease payments arising from the lease. At the inception of the arrangement, the Company determines if an arrangement is a lease based on an assessment of the terms and conditions of the contract. Operating lease ROU assets and lease liabilities are recognized at the commencement date, and thereafter, if modified, based on the present value of lease payments over the lease term. The lease term includes any renewal or early-termination options that the Company is reasonably assured to exercise. The present value of lease payments is determined by using the interest rate implicit in the lease, if that rate is readily determinable; otherwise, the Company uses its estimated secured incremental borrowing rate for that lease term. The underlying assets of the Company’s leases as of the adoption date consisted of office and laboratory space. In March 2017, the FASB issued ASU No. 2017-08, Receivables—Nonrefundable Fees and Other Costs (Subtopic 310-20): Premium Amortization on Purchased Callable Debt Securities (“ASU 2017-08”) which requires companies to amend the amortization period for premiums on debt securities with explicit call features to be the period through the earliest call date rather than through the contractual life of the debt instrument. This amendment aims to more closely align the recognition of interest income with the manner in which market participants price such instruments. The Company adopted the new standard on the effective date of October 1, 2019. The adoption of the standard did not have a material impact on the Company’s financial position and results of operations. In December 2019, the FASB issued ASU No. 2019-12, Simplifying the Accounting for Income Taxes (Topic 740), which removes certain exceptions to the general principles in Topic 740 – Income Taxes and improves consistent application of and simplifies GAAP for other areas of Topic 740 by clarifying and amending existing guidance. This ASU is effective for the Company beginning October 1, 2021 and interim periods within that year, with early adoption permitted. The Company does not expect the adoption of the standard to have a material impact on the Company's financial position or results of operations.

Fair Value of Financial Assets

Fair Value of Financial Assets and Liabilities	12 Months Ended
	Sep. 30, 2021
Fair Value Disclosures [Abstract]
Fair Value of Financial Assets and Liabilities	3. Fair Value of Financial Assets and Liabilities The following tables present information about the Company’s financial assets and liabilities that were subject to fair value measurement on a recurring basis as of September 30, 2021 and 2020 and indicate the fair value hierarchy of the valuation inputs utilized to determine such fair value: Fair Value Measurements at September 30, 2021 Using: Level 1 Level 2 Level 3 Total (in thousands) Assets: Cash equivalents: Money market funds $ 54,819 $ — $ — $ 54,819 Marketable securities: U.S. Treasury notes 83,038 — — 83,038 Corporate bonds — 124,703 — 124,703 Commercial paper — 87,471 — 87,471 $ 137,857 $ 212,174 $ — $ 350,031 Liabilities: Series 1 nonconvertible preferred stock — — 1,506 1,506 $ — $ — $ 1,506 $ 1,506 Fair Value Measurements at September 30, 2020 Using: Level 1 Level 2 Level 3 Total (in thousands) Assets: Cash equivalents: Money market funds $ 81,502 $ — $ — $ 81,502 Marketable securities: U.S. Treasury notes 94,208 — — 94,208 Commercial paper — 93,909 — 93,909 Corporate bonds — 144,035 — 144,035 $ 175,710 $ 237,944 $ — $ 413,654 Liabilities: Series 1 nonconvertible preferred stock — — 1,479 1,479 $ — $ — $ 1,479 $ 1,479 Cash equivalents at September 30, 2021 and 2020 consist of money market funds which are readily convertible to cash and with less than 90 days until maturity. During the years ended September 30, 2021, 2020, and 2019 , there were no transfers between Level 1, Level 2 and Level 3. The fair value of Level 2 instruments classified as marketable securities were determined through third-party pricing services. The pricing services use many observable market inputs to determine value, including reportable trades, benchmark yields, credit spreads, broker/dealer quotes, bids, offers, and current spot rates. The outstanding shares of Series 1 nonconvertible preferred stock as of September 30, 2021 and 2020 were measured at fair value. These outstanding shares were financial instruments that might have required a transfer of assets because of the liquidation features in the contract and were therefore recorded as liabilities and measured at fair value. The fair value of the outstanding shares were based on significant inputs not observable in the market, which represented a Level 3 measurement within the fair value hierarchy. The Company utilized a probability-weighted valuation model which takes into consideration various outcomes that may require the Company to transfer assets upon liquidation. Changes in the fair values of the Series 1 nonconvertible preferred stock are recognized in other income (expense), net in the consolidated statements of operations. The recurring Level 3 fair value measurements of the Company’s Series 1 nonconvertible preferred stock using probability-weighted discounted cash flow include the following significant unobservable inputs: Range September 30, Unobservable Input 2021 2020 Probabilities of payout 0 %- 65 % 0 %- 60 % Discount rate 4.2 5% 4.25 % The following table provides a rollforward of the aggregate fair value of the Company’s outstanding Series 1 nonconvertible preferred stock for which fair value is determined by Level 3 inputs: Series 1 (in thousands) Balance, September 30, 2018 $ 1,628 No change in fair value — Balance, September 30, 2019 1,628 Decrease in fair value ( 149 ) Balance, September 30, 2020 1,479 Increase in fair value 27 Balance, September 30, 2021 $ 1,506

Marketable Securities

Marketable Securities	12 Months Ended
	Sep. 30, 2021
Investments Debt And Equity Securities [Abstract]
Marketable Securities	4. Marketable Securities As of September 30, 2021 and 2020, the fair value of available-for-sale marketable securities, by type of security, was as follows: September 30, 2021 Amortized Gross Gross Credit Losses Fair Value (in thousands) Corporate bonds $ 124,678 $ 93 $ ( 68 ) $ — $ 124,703 Commercial paper 87,471 — — — 87,471 U.S. Treasury notes 83,061 3 ( 26 ) — 83,038 $ 295,210 $ 96 $ ( 94 ) $ — $ 295,212 September 30, 2020 Amortized Gross Gross Credit Losses Fair Value (in thousands) Corporate bonds $ 143,274 $ 775 $ ( 14 ) $ — $ 144,035 Commercial paper 93,909 — — — 93,909 U.S. Treasury notes 93,740 468 — — 94,208 $ 330,923 $ 1,243 $ ( 14 ) $ — $ 332,152 As of September 30, 2021 and 2020 , marketable securities consisted of investments that mature within one year , with the exception of certain corporate bonds and U.S. Treasury notes, which have maturities between one and three years and an aggregate fair value of $ 108,416 and $ 32,634 , respectively.

Property and Equipment, Net

Property and Equipment, Net	12 Months Ended
	Sep. 30, 2021
Property Plant And Equipment [Abstract]
Property and Equipment, Net	5. Property and Equipment, Net Property and equipment, net consisted of the following as of September 30, 2021 and 2020: September 30, 2021 2020 (in thousands) Laboratory and office equipment $ 14,499 $ 14,036 Leasehold improvements 7,140 7,089 Purchased software 1,387 1,364 Furniture 1,294 1,276 Computer equipment 529 505 Construction in progress 20 — 24,869 24,270 Less: Accumulated depreciation and amortization ( 18,926 ) ( 15,674 ) $ 5,943 $ 8,596 Depreciation and amortization expense for property and equipment, including assets acquired under capital leases, was $ 3,334 , $ 3,644 and $ 3,258 for the years ended September 30, 2021, 2020, and 2019 , respectively.

Accrued Expenses and Other Curr

Accrued Expenses and Other Current Liabilities and Other Long-Term Liabilities	12 Months Ended
	Sep. 30, 2021
Payables And Accruals [Abstract]
Accrued Expenses and Other Current Liabilities and Other Long-Term Liabilities	6. Accrued Expenses and Other Current Liabilities and Other Long-Term Liabilities Accrued expenses and other current liabilities and other long-term liabilities consisted of the following as of September 30, 2021 and 2020: September 30, 2021 2020 Accrued expenses and other current liabilities: (in thousands) Accrued research and development expenses $ 6,062 $ 5,407 Accrued payroll and related expenses 6,094 4,777 Accrued pharmaceutical drug manufacturing 8,402 2,885 Accrued professional fees 700 478 Accrued other 1,171 612 $ 22,429 $ 14,159 Other long-term liabilities: Uncertain tax positions $ 558 $ 788 Asset retirement obligation — 290 $ 558 $ 1,078

Collaboration Agreements

Collaboration Agreements	12 Months Ended
	Sep. 30, 2021
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Collaboration Agreements	7. Collaboration Agreements AbbVie Collaboration On November 27, 2006 , the Company entered into a Collaborative Development and License Agreement (the “AbbVie Agreement”) with Abbott Laboratories to identify, develop and commercialize HCV NS3 and NS3/4A protease inhibitor compounds, including paritaprevir and glecaprevir. The agreement was assigned by Abbott to AbbVie Inc. on January 1, 2013 in connection with Abbott’s transfer of its research-based pharmaceuticals business to AbbVie. Under the terms of the AbbVie Agreement, as amended, AbbVie paid the Company upfront license payments and full-time equivalent (“FTE”) reimbursements to fund research activities. The Company is also eligible to receive milestone payments for the successful development by AbbVie of one or more HCV compounds, as well as annually tiered, per-product royalties on the portion of AbbVie’s net sales of its HCV treatment regimens allocated to the protease inhibitor product. The Company determined that the deliverables under the AbbVie Agreement included (i) the non-exclusive, royalty-free, worldwide research license and the exclusive, royalty-bearing development and commercialization license, (ii) the research services, and (iii) a commitment to participate on a steering committee, all of which were to be delivered over a three-year period. The Company concluded that the license did not have standalone value as it was dependent, in part, upon the Company’s continuing involvement in the HCV protease inhibitor research and its involvement in the joint steering committee. Additionally, the undelivered items, including the Company’s participation in the joint steering committee, which was considered participatory due to its decision making responsibilities, and the research services, did not have vendor-specific objective evidence (“VSOE”) or vendor objective evidence (“VOE”) of fair value. Therefore, the license, the research services, and the joint steering committee participation were treated as a single unit of accounting. Accordingly, all amounts received were deferred, and revenue was recognized using the proportional performance model over the period during which the Company performed research services in connection with the AbbVie Agreement, as amended. Subsequent to the research and evaluation period, which ended in June 2011, all decisions related to the development, commercialization and marketing have been made by AbbVie. The Company has the right to continue to attend the joint steering committee meetings to monitor the development and marketing plans; however, the Company has no decision-making rights. As such, the joint steering committee commitment became protective in nature as of June 16, 2011. From commencement of the collaboration through September 30, 2021 the Company has received an upfront license payment, research funding, milestone payments, and preferred stock financing totaling $ 396,000 under the AbbVie agreement. Since the Company completed all its performance obligations under the AbbVie Agreement by the end of fiscal 2011, any milestone payments earned since then have been recognized as revenue when the associated milestone was achieved by AbbVie. The Company is also receiving annually tiered royalties per Company protease product ranging from ten percent up to twenty percent, or on a blended basis from the low double digits up to the high teens, on the portion of AbbVie’s calendar year net sales of each HCV regimen that is allocated to the protease inhibitor product in the regimen. Beginning with each January 1, the cumulative net sales of a given royalty-bearing protease inhibitor product start at zero for purposes of calculating the tiered royalties on a product-by-product basis. The following table details the royalty tiers associated with cumulative calendar year net sales allocated to each royalty-bearing product as provided in the AbbVie Agreement: Calendar Year Net Sales Royalty Tier (in thousands) (%) up to $ 500,000 10 % from $ 500,000 up to $ 750,000 12 % from $ 750,000 up to $ 1,000,000 14 % from $ 1,000,000 up to $ 2,500,000 17 % greater than or equal to $ 2,500,000 20 % Royalties owed to the Company under the agreement can be reduced by AbbVie in certain circumstances, including (i) if AbbVie exercises its right to license or otherwise acquire rights to intellectual property controlled by a third party where a product could not be legally developed or commercialized in a country without the third-party intellectual property right, (ii) where a product developed under the collaboration agreement is sold in a country and not covered by a valid patent claim in such country, and (iii) where sales of a generic product are equal to at least a specified percentage of AbbVie’s market share of its product in a country. AbbVie’s obligation to pay royalties on a product developed under the agreement expires on a country-by-country basis upon the later of (i) the date of expiration of the last of the licensed patents with a valid claim covering the product in the applicable country, or (ii) ten years after the first commercial sale of the product in the applicable country. Subject to certain exceptions, a party’s rights and obligations under the agreement continue until (i) such time as AbbVie is no longer developing a product candidate or (ii) if, as of the time AbbVie is no longer developing any product candidates, AbbVie is commercializing any other protease inhibitor product, such time as all royalty terms for all covered products have ended. Accordingly, the final expiration date of the agreement is currently indeterminable. Either party may terminate the agreement for cause in the event of a material breach, subject to prior notice and the opportunity to cure, or in the event of the other party’s bankruptcy. Additionally, AbbVie may terminate the agreement for any reason upon specified prior notice. If the Company terminates the agreement for cause or AbbVie terminates without cause, any licenses and other rights granted to AbbVie will terminate and AbbVie will be deemed to have granted the Company (i) a non-exclusive, perpetual, fully-paid, worldwide, royalty-free license, with the right to sublicense, under AbbVie’s intellectual property used in any product candidate, and (ii) an exclusive (even as to AbbVie), perpetual, fully-paid, worldwide, royalty-free license, with the right to sublicense, under AbbVie’s interest in any joint intellectual property rights to develop product candidates resulting from covered compounds and to commercialize any products derived from such compounds. Upon the Company’s request, AbbVie will also transfer to the Company all right, title and interest in any related product trademarks, regulatory filings and clinical trials. If AbbVie terminates the agreement for the Company’s uncured breach, the milestone and royalty payments payable by AbbVie may be reduced, the licenses granted to AbbVie will remain in place, the Company will be deemed to have granted AbbVie an exclusive license under the Company’s interest in joint intellectual property, AbbVie will continue to have the right to commercialize any covered products, and all rights and licenses granted to the Company by AbbVie will terminate.

Stockholders' Equity

Stockholders' Equity	12 Months Ended
	Sep. 30, 2021
Equity [Abstract]
Stockholders' Equity	8. Stockholders’ Equity The Company is authorized to issue 100,000 shares of common stock at a par value of $ 0.01 per share. Each share of common stock entitles the holder to one vote on all matters submitted to a vote of the Company’s stockholders. Common stockholders are entitled to receive such dividends as may be declared by the board of directors, if any. The Company also is authorized to issue 5,000 shares of preferred stock at a par value of $ 0.01 per share, of which 2,000 shares are designated as Series 1 Nonconvertible preferred stock and 3,000 shares are undesignated and unissued.

Series 1 Nonconvertible Preferr

Series 1 Nonconvertible Preferred Stock and Warrants	12 Months Ended
	Sep. 30, 2021
Debt Disclosure [Abstract]
Series 1 Nonconvertible Preferred Stock and Warrants	9. Series 1 Nonconvertible Preferred Stock and Warrants The Company’s Certificate of Incorporation authorizes the issuance of up to 2,000 shares of Series 1 nonconvertible preferred stock at a par value of $ 0.01 per share. Holders of Series 1 nonconvertible preferred stock are not entitled to receive dividends. In the event of any liquidation, deemed liquidation, dissolution or winding up of the Company, the Series 1 nonconvertible preferred stockholders are entitled to receive in preference to all other stockholders, an amount equal to $ 1.00 per share, adjusted for any stock dividends, stock splits or reclassifications. Series 1 nonconvertible preferred stockholders will not be entitled to vote unless required by the Company pursuant to the laws of the State of Delaware. The Company may redeem the Series 1 nonconvertible preferred stock with the approval of the holders of a majority of the outstanding shares of Series 1 nonconvertible preferred stock at a redemption price of $ 1.00 per share. The Company must redeem the stock within 60 days of such election. Shares that are redeemed will be retired or canceled and not reissued by the Company. As these shares qualify as a derivative, they are classified as a liability on the Company’s consolidated balance sheet. In October and November 2010, a total of 2,000 warrants to purchase Series 1 nonconvertible preferred stock were issued. The warrants had an expiration date of October 4, 2017 and any warrants exercised by that date were converted into Series 1 nonconvertible preferred stock. A total of 1,930 shares of Series 1 nonconvertible preferred stock were outstanding as of September 30, 2021 and 2020. For the years ended September 30, 2021, 2020, and 2019 , the remeasurement of the Series 1 nonconvertible preferred stock resulted in income (expense) of $( 27 ), $ 149 , and $ 0 , respectively, which was recorded in other income (expense), net in the consolidated statements of operations. The total fair value of the Series 1 nonconvertible preferred stock was $ 1,506 and $ 1,479 as of September 30, 2021 and 2020 , respectively.

Stock-Based Awards

Stock-Based Awards	12 Months Ended
	Sep. 30, 2021
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Stock-Based Awards	10. Stock-Based Awards The Company’s 2019 Equity Incentive Plan (the “2019 Plan”) permits the Company to sell or issue awards of common stock or restricted common stock or to grant awards of incentive stock options or nonqualified stock options for the purchase of common stock, restricted stock units, performance units, stock appreciation rights or other cash incentive awards, to employees, members of the board of directors and consultants of the Company. The number of shares of common stock that may be issued under the 2019 Plan is subject to increase by the number of shares forfeited under any options forfeited and not exercised under the 2019 Plan or any predecessor plans such as the 2012 Equity Incentive Plan or the 1995 Equity Incentive Plan. As of September 30, 2021, 1,093 shares remained available for future awards under the 2019 Plan. The 2019 Plan replaces and is the successor to the 2012 Equity Incentive Plan (the “2012 Plan”) and the 1995 Equity Incentive Plan (the “1995 Plan”). The 2012 and 1995 Plans provided for the Company to sell or issue awards of common stock or restricted common stock, or to grant awards of incentive stock options or nonqualified stock options for the purchase of common stock, to employees, members of the board of directors and consultants of the Company. Sales, issuances or grants of shares entitle the holder to purchase common stock from the Company, for a specified exercise price, during a period specified by the applicable equity award agreement. Upon the closing of the Company’s initial public offering, all remaining shares reserved for issuance under the 1995 Plan were transferred to the 2012 Plan and no further awards were made under the 1995 Plan. Upon the approval of the 2019 Plan by the Company’s shareholders in February 2019, all remaining shares reserved for issuance under the 2012 Plan were transferred to the 2019 Plan and no further awards have been made under the 2012 Plan. Under the Company’s Employee Stock Purchase Plan (“ESPP”) a total of 186 shares of common stock are reserved for issuance. As of September 30, 2021 , the Company had not commenced any offering under the ESPP and no ESPP shares have been issued. The Company applies the fair value recognition provisions for all stock-based awards granted or modified. In the case of service-based awards, the compensation cost is recorded over the requisite service period of the award on the straight-line method based on the grant-date fair value. The requisite service period for service-based option awards is generally four years . Options granted under the 2019 Plan to employees generally vest over four years and to non-employee directors over one year , and expire after ten years . Stock Option Valuation The fair value of each stock option award is determined on the date of grant using the Black-Scholes option-pricing model. The volatility has been determined using the Company’s traded stock price following our March 2013 IPO to estimate expected volatility. The expected term of the Company’s options has been determined utilizing the “simplified” method for awards that qualify as “plain-vanilla” options. 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. The expected dividend yield is zero on the fact that the Company has never paid cash dividends and does not expect to pay any cash dividends in the foreseeable future. As required under our equity plans, the exercise price for awards granted is not to be less than the fair value of common shares as estimated by the Company as of the date of grant. The relevant data used to determine the value of the stock option awards are as follows, presented on a weighted average basis: Years Ended September 30, 2021 2020 2019 Risk-free interest rate 0.61 % 1.41 % 2.76 % Expected term (in years) 6.05 6.02 6.05 Expected volatility 52 % 53 % 55 % Expected dividends 0 % 0 % 0 % Weighted average grant date fair value $ 21.76 $ 30.47 $ 44.66 The following table summarizes stock option activity, including aggregate intrinsic value for the year ended September 30, 2021: Shares Weighted Weighted Aggregate (in thousands) (in thousands) Outstanding as of September 30, 2020 3,262 $ 49.82 6.5 $ 21,860 Granted 901 45.01 Exercised ( 129 ) 27.99 Forfeited ( 182 ) 67.01 Outstanding as of September 30, 2021 3,852 $ 48.61 6.4 $ 49,173 Options vested and expected to vest as of September 30, 2021 3,852 $ 48.61 6.4 $ 49,173 Options exercisable as of September 30, 2021 2,520 $ 45.91 5.2 $ 39,356 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. The following tables summarize additional exercise and grant date information: Years Ended September 30, 2021 2020 2019 (in thousands) Aggregate intrinsic value of stock options exercised $ 2,704 $ 7,850 $ 13,855 Proceeds to Company from stock options exercised $ 3,614 $ 10,481 $ 6,848 Market and Performance-Based Stock Unit Awards The Company awards both performance share units, or PSUs, and relative total stockholder return units, or rTSRUs, to its executive officers. The PSUs vest and result in issuance, or settlement, of common shares for each recipient, based upon the recipient’s continued employment with the Company through the settlement date of the award and the Company’s achievement of specified research and development milestones. The requisite service period of the PSUs is generally 2 years. The fair value of PSUs is based on the fair value of the stock on the date of grant which is determined to be the closing price of our common stock. The fair value of PSUs is recorded in the financial statements when it is probable that the specified research and development milestone is achieved. The rTSRUs vest and result in the issuance of common stock based upon the recipient’s continuing employment with the Company through the settlement date of the award and the relative ranking of the total stockholder return, or TSR, of the Company’s common stock in relation to the TSR of the component companies in the NASDAQ Biotech Index over two specified periods that are two years apart, based on a comparison of average closing stock prices in specified periods noted in the award agreement. The number of market-based rTSRUs awarded represents the target number of shares of common stock that may be earned; however, the actual number of shares that may be earned ranges from 0 % to 150 % of the target number, depending on the award agreement and the year of the award. The Company used a Monte Carlo model to estimate the grant-date fair value of the rTSRUs. Assumptions and estimates utilized in the calculation of the fair value of the rTSRUs include the risk-free interest rate, dividend yield, expected volatility based on the historical volatility of publicly traded peer companies and the remaining performance period of the award. The table below sets forth the weighted average grant date fair value assumptions used to value the rTSRUs: Years Ended September 30, 2021 2020 2019 Risk-free interest rate 0.13 % 1.62 % 2.65 % Dividend yield 0 % 0 % 0 % Expected volatility 74 % 68 % 62 % Remaining performance period (years) 1.97 2.03 2.03 The following table summarizes PSU and rTSRU activity (at target) for the year ended September 30, 2021: PSUs rTSRUs Shares Weighted Shares Weighted (in thousands, except per share data) Unvested at September 30, 2020 46 $ 65.23 46 $ 46.46 Granted 84 44.58 84 26.55 Vested — — — — Cancelled ( 19 ) 67.13 ( 19 ) 47.42 Unvested at September 30, 2021 111 $ 49.31 111 $ 31.26 A total of 80 % of target PSUs and 200 % of target rTSRUs granted in January 2017 vested during the year ended September 30, 2019, resulting in the issuance of an aggregate of 125 common shares, net of share withholding for income taxes. A total of 15 % of target PSUs and 90 % of target rTSRUs granted in March 2018 vested during the year ended September 30, 2020, resulting in the issuance of 23 common shares, net of share withholding for income taxes. The total fair value of PSUs and rTSRUs vested during the years ended September 30, 2021, 2020, and 2019 were $ 0 , $ 1,227 and $ 11,074 , respectively. Restricted Stock Units In November 2016, the Company awarded restricted stock units to its employees, which vest as to 50 % of the units on the third anniversary of the award and 50 % on the fourth anniversary of the award, provided the employee remains employed with the Company at the time of vesting. The fair value of these awards was determined based on the fair value of the stock on the date of grant which is determined to be the closing price of the common stock on November 15, 2016 and is recognized as stock-based compensation expense over the requisite service period. The following table summarizes the restricted stock unit activity for the year to date period ending September 30, 2021: Restricted Weighted (in thousands, except per share data) Unvested at September 30, 2020 45 $ 30.00 Granted 123 43.57 Vested ( 45 ) 30.00 Cancelled ( 6 ) 41.40 Unvested at September 30, 2021 117 $ 43.57 The total fair value of restricted stock units vested during the years ended September 30, 2021, 2020, and 2019 were $ 1,897 , $ 3,149 and $ 0 , respectively. Stock-Based Compensation Expense The Company recorded the following stock-based compensation expense for the years ended September 30, 2021, 2020, and 2019: Years Ended September 30, 2021 2020 2019 (in thousands) Research and development $ 10,075 $ 10,096 $ 8,833 General and administrative 10,916 9,479 10,393 $ 20,991 $ 19,575 $ 19,226 Years Ended September 30, 2021 2020 2019 (in thousands) Stock options $ 18,004 $ 17,459 $ 15,854 rTSRUs 1,537 1,216 1,568 PSUs 235 259 1,278 Restricted stock units 1,215 641 526 $ 20,991 $ 19,575 $ 19,226 As of September 30, 2021, the Company had an aggregate of $ 42,222 of unrecognized stock-based compensation cost, which is expected to be recognized over a weighted average period of 2.3 years.

Net Income (Loss) Per Share

Net Income (Loss) Per Share	12 Months Ended
	Sep. 30, 2021
Earnings Per Share [Abstract]
Net Income (Loss) Per Share	11. Net Income (Loss) Per Share Basic and diluted net income (loss) per common share was calculated as follows for the years ended September 30, 2021, 2020, and 2019: Years Ended September 30, 2021 2020 2019 (in thousands, except per share data) Basic net income (loss) per share: Numerator: Net income (loss) $ ( 78,996 ) $ ( 36,168 ) $ 46,383 Denominator: Weighted average common shares outstanding — basic 20,171 19,940 19,584 Net income (loss) per share common share — basic $ ( 3.92 ) $ ( 1.81 ) $ 2.37 Diluted net income (loss) per share: Numerator: Net income (loss) $ ( 78,996 ) $ ( 36,168 ) $ 46,383 Denominator: Weighted average common shares outstanding — basic 20,171 19,940 19,584 Dilutive effect of common stock equivalents — — 1,384 Weighted average common shares outstanding — diluted 20,171 19,940 20,968 Net income (loss) per share common share — diluted $ ( 3.92 ) $ ( 1.81 ) $ 2.21 Anti-dilutive common stock equivalents excluded from above 4,297 3,502 843 The impact of certain common stock equivalents were excluded from the computation of diluted net income per common share for the years ended September 30, 2021, 2020, and 2019, because those awards had an anti-dilutive impact due to the assumed proceeds per share using the treasury stock method being greater than the average fair value of the Company’s common shares for those periods. In addition, for periods in which the Company reported a net loss no dilution was reported. As of September 30, 2019, the Company excluded unvested performance stock unit awards from the calculation of diluted net income per common share as these awards contain performance conditions that would not have been achieved as of the end of each reporting period had the measurement period ended as of that date.

Leases

Leases	12 Months Ended
	Sep. 30, 2021
Leases [Abstract]
Leases	12. Leases The Company has two real estate leases for properties located in Watertown, Massachusetts. The first lease, for office and laboratory space at 500 Arsenal Street, was effective in fiscal 2011 and expires in September 2022 with an option to extend the lease term for an additional five years. The second lease, for office space located at 400 Talcott Avenue, was effective September 2018 and expires in August 2024 with two options to extend the lease term for an additional three years each. The options to extend the lease terms were not included in the right-of-use assets and lease liabilities as they were not reasonably certain of being exercised. The lease payments for the office and laboratory space include fixed lease payments that escalate over the terms of the leases. Additionally, t he Company’s office and laboratory space leases require the Company to pay for certain operating expenses based on actual costs incurred and therefore as the amounts are variable in nature are expensed in the period incurred and included in variable lease costs. The leases do not include any restrictions or covenants that had to be accounted for under the lease guidance. In October 2019, the Company entered into an agreement to lease units of equipment over eighteen-month lease periods commencing upon shipment of each unit. The lease agreement contains an option to terminate the lease early, however this early-termination option was not included in the right-of-use asset and lease liability as it was not reasonably certain of being exercised. The equipment lease requires the Company to pay for certain consumable and peripheral equipment supplies based on actual costs incurred and therefore, as these costs are variable in nature, they are expensed in the period incurred and included in variable lease costs. The components of lease expense for the Company’s real estate and equipment leases were as follows: Years Ended September 30, 2021 2020 (in thousands) Operating lease cost $ 5,861 $ 3,776 Short-term lease cost — — Variable lease cost 4,057 2,338 $ 9,918 $ 6,114 Years Ended September 30, 2021 2020 (in thousands) Cash paid for amounts included in the measurement of operating lease liabilities $ 6,364 $ 4,126 Operating lease liabilities arising from obtaining right-of-use assets $ 3,320 $ 3,053 September 30, 2021 2020 Weighted-average remaining lease term - operating leases (in years) 1.43 2.20 Weighted-average discount rate - operating leases 6.08 % 6.50 % As the Company’s leases do not provide an implicit rate, the Company utilized its incremental borrowing rate based on information available at the lease commencement date, which represents an internally developed rate that would be incurred to borrow, on a collateralized basis, over a similar term, an amount equal to the lease payments in a similar economic environment. Future annual minimum lease payments under the Company’s real estate and equipment operating leases as of September 30, 2021 were as follows: Years ended September 30, (in thousands) 2022 4,391 2023 675 2024 519 2025 — 2026 — Total future minimum lease payments 5,585 Less: Imputed interest ( 256 ) Total operating lease liabilities $ 5,329 Included in the balance sheet: 2021 2020 (in thousands) Current operating lease liabilities $ 4,203 $ 4,261 Operating lease liabilities, net of current portion 1,126 3,838 Total operating lease liabilities $ 5,329 $ 8,099 In connection with one of the real estate leases, the Company has a total outstanding letter of credit in the amount of $ 608 as of September 30, 2021 and 2020 collateralized by a money market account. As of September 30, 2021 and 2020, the Company classified the $ 608 related to the money market account as long-term restricted cash.

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Sep. 30, 2021
Commitments And Contingencies Disclosure [Abstract]
Commitments and Contingencies	13. Commitments and Contingencies Litigation and Contingencies Related to Use of Intellectual Property From time to time, the Company may become subject to legal proceedings, claims and litigation arising in the ordinary course of business. The Company currently is not a party to any threatened or pending litigation. However, third parties might allege that the Company or its collaborators are infringing their patent rights or that the Company is otherwise violating their intellectual property rights. Such third parties may resort to litigation against the Company or its collaborators, which the Company has agreed to indemnify. With respect to some of these patents, the Company expects that it will be required to obtain licenses and could be required to pay license fees or royalties, or both. These licenses may not be available on acceptable terms, or at all. A costly license, or inability to obtain a necessary license, would have a material adverse effect on the Company’s financial condition, results of operations or cash flows. The Company accrues contingent liabilities when it is probable that future expenditures will be made and such expenditures can be reasonably estimated. Indemnification Agreements In the ordinary course of business, the Company may provide indemnifications of varying scope and terms to customers, vendors, lessors, business partners, and other parties with respect to certain matters including, but not limited to, losses arising out of breach of such agreements or from services to be provided to the Company, or from intellectual property infringement claims made by third parties. In addition, the Company has entered into indemnification agreements with members of its board of directors and its executive officers that will require the Company, among other things, to indemnify them against certain liabilities that may arise by reason of their status or service as directors or officers. The maximum potential amount of future payments the Company could be required to make under these indemnification agreements is, in many cases, unlimited. To date, the Company has not incurred any material costs as a result of such indemnifications. In addition, the Company maintains officers and directors insurance coverage. The Company does not believe that the outcome of any claims under indemnification arrangements will have a material effect on its financial position, results of operations or cash flows, and has not accrued any liabilities related to such obligations in its financial statements as of September 30, 2021 and 2020 .

Income Taxes

Income Taxes	12 Months Ended
	Sep. 30, 2021
Income Tax Disclosure [Abstract]
Income Taxes	14. Income Taxes Income before income taxes for all periods presented is from domestic operations, which are the Company’s only operations. During the years ended September 30, 2021, 2020, and 2019, the Company recorded income tax benefit (expense) as follows: Years Ended September 30, 2021 2020 2019 (in thousands) Current income tax benefit (expense): Federal $ 28,721 $ 8,491 $ ( 1,841 ) State 205 941 ( 372 ) Deferred income tax benefit (expense): Federal ( 343 ) ( 8,916 ) 2,431 State — ( 1,665 ) 608 Income tax (expense) benefit $ 28,583 $ ( 1,149 ) $ 826 A reconciliation of the U.S. federal statutory income tax rate to the Company’s effective tax rate is as follows: Years Ended September 30, 2021 2020 2019 Federal statutory income tax rate ( 21.0 %) ( 21.0 %) 21.0 % State taxes, net of federal benefit ( 2.3 ) ( 2.8 ) 1.8 Change in valuation allowance 9.9 52.1 — Federal research and development tax credit ( 5.3 ) ( 13.3 ) ( 12.8 ) Share-based compensation 2.4 2.8 ( 6.7 ) Change in deferred tax rate ( 9.5 ) ( 10.2 ) — Foreign-derived intangible income — — ( 3.2 ) Other ( 0.8 ) ( 4.3 ) ( 1.9 ) Effective income tax rate ( 26.6 %) 3.3 % ( 1.8 %) The negative federal statutory income tax rate during the years ended September 30, 2021 and 2020 reflects an income tax benefit due to the Company’s ability to carryback the pre-tax loss for the year under the Coronavirus Aid, Relief and Economic Security Act (“CARES Act”). The Company recorded an income tax receivable of $ 37,255 and $ 13,041 as of September 30, 2021 and 2020 which primarily consists of the federal net operating loss carryback generated during the years ended September 30, 2021 and 2020. Changes in the valuation allowance for deferred tax assets during the years ended September 30, 2021, 2020, and 2019 are as follows: Years Ended September 30, 2021 2020 2019 (in thousands) Valuation allowance, beginning of year $ ( 18,259 ) $ — $ — Increase recorded to valuation allowance ( 11,039 ) — — Initial recording of valuation allowance — ( 18,259 ) — Valuation allowance, end of year $ ( 29,298 ) $ ( 18,259 ) $ — Net deferred tax assets as of September 30, 2021 and 2020 consisted of the following: September 30, 2021 2020 (in thousands) Deferred tax assets: Share-based compensation $ 11,843 $ 11,071 Tax credit carryforwards 13,170 6,574 Operating lease liability 1,232 2,468 Accrued compensation 1,284 1,598 Net operating loss carryforward 3,095 861 Accrued expenses 378 245 Other temporary differences 366 444 Total deferred tax assets 31,368 23,261 Valuation allowance ( 29,298 ) ( 18,259 ) Net deferred tax assets 2,070 5,002 Deferred tax liabilities: Right of use asset ( 1,110 ) ( 2,221 ) Depreciation ( 684 ) ( 1,650 ) Prepaid expenses ( 275 ) ( 364 ) Unrealized loss ( 1 ) ( 422 ) Total deferred tax liabilities ( 2,070 ) ( 4,657 ) Net deferred income tax assets (liabilities) $ — $ 345 The net deferred tax asset is presented as a long-term asset on the consolidated balance sheets. As of September 30, 2021, the Company had a federal and state research and developm ent tax credit carryforward of $ 11,251 and $ 2,058 , respectively, for tax return purposes, a m ajority of which begin to expire in 2039 . In addition, the Company had state net operating losses of $ 3,095 as of September 30, 2021 which begin to expire in 2040 . As of September 30, 2021 , the Company has $ 29,298 in net deferred tax assets, prior to consideration of a valuation allowance. These deferred tax assets include $ 11,843 related to stock compensation awards that would create a tax benefit in the future against future taxable income and federal research and development tax credit carryforwards totaling $ 13,170 . The Company considers it more likely that it will not have sufficient taxable income in the future that will allow it to realize all of its existing deferred tax assets. This is due to the fact the Company continues to progress its wholly-owned research and development programs and its declining royalty revenues from its Collaboration Agreement with AbbVie. As a result, the Company continued to record a valuation allowance of $ 29,298 as of September 30, 2021 against its deferred tax assets to reduce a portion of the Company’s deferred tax assets for which the Company does not believe it is more likely than not these will be realized. The Company files tax returns as prescribed by the tax laws of the jurisdictions in which it operates. In the normal course of business, the Company is subject to examination by federal and state jurisdictions, where applicable. The Company’s tax years in the U.S. are still open under statute from 2017 to the present. Earlier years may be examined to the extent that tax credit or net operating loss carryforwards are used in future periods. The Company has not received notice of examination by any other jurisdictions for any other tax year open under statute. In response to the COVID-19 pandemic, the CARES Act was signed into law in March 2020. The CARES Act lifts certain deduction limitations originally imposed by the Tax Cuts and Jobs Act of 2017 (the “Tax Act”). Under the CARES Act, the Company is permitted to carryback net operating losses for up to five years for losses generated in fiscal 2018 through fiscal 2021. Net operating loss carrybacks were previously prohibited under the Tax Act. The CARES Act also eliminates the 80% of taxable income limitations by allowing corporate entities to fully utilize net operating loss carryforwards to offset taxable income in fiscal years 2018, 2019 or 2020. In addition, the CARES Act makes qualified improvement property eligible for 15-year cost-recovery and 100% bonus depreciation. The enactment of the CARES Act resulted in a $ 28,721 and $ 8,581 income tax benefit related to a federal net operating loss carryback at the previously enacted 35 % rate in the Company’s consolidated financial statements during the years ended September 30, 2021 and 2020 , respectively. Uncertain tax positions represent tax positions for which reserves have been established. The Company’s policy is to record interest and penalties related to uncertain tax positions as part of income tax expense. Total interest related to uncertain tax positions recorded as a liability on the Company’s consolidated balance sheets were $ 105 and $ 103 as of September 30, 2021 and 2020 , respectively. A reconciliation of the beginning and ending amount of uncertain tax positions is summarized as follows: September 30, 2021 2020 (in thousands) Beginning Balance $ 844 $ 1,650 Additions based on tax positions for the current period 10 11 Reductions for tax positions due to lapse of statute of limitations ( 134 ) ( 719 ) Reductions for tax positions of prior periods ( 98 ) ( 98 ) Ending Balance $ 622 $ 844 The Company does not expect that its uncertain tax position will materially change within the next twelve months.

401(k) Plan

401(k) Plan	12 Months Ended
	Sep. 30, 2021
Postemployment Benefits [Abstract]
401(k) Plan	15. 401(k) Plan The Company has a 401(k) plan. This plan covers substantially all employees who meet minimum age and service requirements. During the years ended September 30, 2021, 2020, and 2019, the Company recognized $ 1,353 , $ 1,190 , and $ 1,068 respectively, of expense related to its contributions to this plan.

Subsequent Events

Subsequent Events	12 Months Ended
	Sep. 30, 2021
Subsequent Events [Abstract]
Subsequent Events	16. Subsequent Events On November 19, 2021, the Company exercised its option to extend the lease term of its existing office and laboratory space at 500 Arsenal Street for an additional 5 years through September 1, 2027 . The updated minimum lease payments related to the 500 Arsenal Street lease as a result of the extension are as follows: Years ended September 30, (in thousands) 2022 2,487 2023 3,502 2024 3,607 2025 3,715 2026 3,827 Thereafter 3,604 Total future minimum lease payments $ 20,742

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Sep. 30, 2021
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The accompanying consolidated financial statements include those of the Company and its subsidiary, Enanta Pharmaceuticals Security Corporation, after elimination of all intercompany accounts and transactions. The accompanying consolidated financial statements have been prepared in conformity with accounting principles generally accepted in the United States of America (“GAAP”).
Use of Estimates	Use of Estimates The preparation of consolidated financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, the disclosure of contingent assets and liabilities at the date of the consolidated financial statements, and the reported amounts of revenues and expenses during the reporting period. Significant estimates and assumptions reflected in these consolidated financial statements include, but are not limited to, management’s judgments with respect to its revenue arrangements; valuation of stock-based awards and the accrual of research and development expenses. Estimates are periodically reviewed in light of changes in circumstances, facts and experience. The future developments of the COVID-19 pandemic also may directly or indirectly impact the Company’s business. The Company has made estimates of the impact of COVID-19 in the Company’s consolidated financial statements as of September 30, 2021 . Actual results could differ from the Company’s estimates.
Cash Equivalents and Marketable Securities	Cash Equivalents and Marketable Securities The Company considers all short-term, highly liquid investments with original maturities of ninety days or less at acquisition date to be cash equivalents. Marketable securities with original maturities of greater than ninety days and remaining maturities of less than one year from the balance sheet date are classified as short-term marketable securities. Marketable securities with remaining maturities of greater than one year from the balance sheet date are classified as long-term marketable securities. The Company classifies all of its marketable securities as available-for-sale. The Company continually evaluates the credit ratings of its investment portfolio and underlying securities. The Company invests in accordance with its investment policy and invests at the date of purchase in securities with a rating of A3/A- or higher according to Moody’s or S&P or A- by Fitch. The Company reports available-for-sale investments at fair value as of each balance sheet date and records any unrealized gains or losses as a component of stockholders’ equity. The cost of securities sold is determined on a specific identification basis, and realized gains and losses are included in other income (expense), net within the consolidated statements of operations. When the fair value is below the amortized cost of a marketable security, an estimate of expected credit losses is made. The credit-related impairment amount is recognized in the consolidated statements of operations. Credit losses are recognized through the use of an allowance for credit losses account in the consolidated balance sheet and subsequent improvements in expected credit losses are recognized as a reversal of an amount in the allowance account. If the Company has the intent to sell the security or it is more likely than not that the Company will be required to sell the security prior to recovery of its amortized cost basis, then the allowance for the credit loss is written-off and the excess of the amortized cost basis of the asset over its fair value is recorded in the consolidated statements of operations. There were no credit losses recorded during the years ended September 30, 2021, 2020, and 2019 .
Restricted Cash	Restricted Cash As of September 30, 2021 and 2020 the Company had an outstanding letter of credit collateralized by a money market account of $ 608 to the benefit of the landlord of one of the Company’s existing building leases. This amount was classified as long-term restricted cash as of September 30, 2021 and 2020 .
Concentration of Credit Risk and of Significant Customers and Suppliers	Concentration of Credit Risk and of Significant Customers and Suppliers Financial instruments that potentially expose the Company to concentrations of credit risk consist primarily of cash, cash equivalents, marketable securities and accounts receivable. The Company has all cash and investment balances at one accredited financial institution, including cash in amounts that exceed federally insured limits. The Company does not believe that it is subject to unusual credit risk beyond the normal credit risk associated with commercial banking relationships. The Company has historically generated the majority of its revenue from its collaborative research and license agreements. As of September 30, 2021 and 2020, accounts receivable consisted of amounts due from the Company’s principal collaborator (see Note 7). The Company is completely dependent on third-party manufacturers for product supply for preclinical and clinical research activities. The Company relies and expects to continue to rely exclusively on several manufacturers to supply the Company with its drug supply requirements related to these activities. These research programs would be adversely affected by a significant interruption in the supply from these third-party manufacturers.
Fair Value Measurements	Fair Value Measurements Certain assets and liabilities are carried at fair value under GAAP. Fair value is defined as the exchange price that would be received for an asset or paid to transfer a liability (an exit price) in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants on the measurement date. Valuation techniques used to measure fair value must maximize the use of observable inputs and minimize the use of unobservable inputs. A fair value hierarchy is based on three levels of inputs which are used to measure fair value, of which the first two levels are considered observable and the last is considered unobservable:  Level 1—Quoted prices in active markets for identical assets or liabilities.  Level 2—Observable inputs (other than Level 1 quoted prices) such as quoted prices in active markets for similar assets or liabilities, quoted prices in markets that are not active for identical or similar assets or liabilities, or other inputs that are observable or can be corroborated by observable market data.  Level 3—Unobservable inputs that are supported by little or no market activity and that are significant to determining the fair value of the assets or liabilities, including pricing models, discounted cash flow methodologies and similar techniques. The Company’s instruments that are carried at fair value are cash equivalents, marketable securities and the Series 1 nonconvertible preferred stock. The carrying values of accounts receivable, prepaid and other assets, accounts payable and accrued expenses approximate their fair value due to the short-term nature of these assets and liabilities.
Property and Equipment	Property and Equipment Property and equipment are stated at cost less accumulated depreciation. Depreciation expense is recognized using the straight-line method over the following estimated useful lives: Laboratory and office equipment 5 years Leasehold improvements Shorter of life of lease or estimated useful life Purchased software 3 years Computer equipment 3 years Furniture 7 years Expenditures for repairs and maintenance of assets are charged to expense as incurred. Costs of major additions and betterments are capitalized and depreciated on a straight-line basis over their useful lives. Upon retirement or sale, the cost and related accumulated depreciation of assets disposed are removed from the accounts and any resulting gain or loss is included in income from operations in the consolidated statements of operations.
Impairment of Long-Lived Assets	Impairment of Long-Lived Assets The Company reviews long-lived assets, primarily property and equipment, for impairment whenever events or changes in business circumstances indicate that the carrying amount of the assets may not be fully recoverable. Factors that the Company considers in deciding when to perform an impairment review include significant underperformance of the business in relation to expectations, significant negative industry or economic trends, and significant changes or planned changes in the use of the assets. If an impairment review is performed to evaluate a long-lived asset for recoverability, the Company compares forecasts of undiscounted cash flows expected to result from the use and eventual disposition of the long-lived asset to its carrying value. An impairment loss would be recognized when estimated undiscounted future cash flows expected to result from the use of an asset are less than its carrying amount. The impairment loss would be based on the excess of the carrying value of the impaired asset over its fair value, determined based on discounted cash flows. To date, the Company has not recorded any impairment losses on long-lived assets.
Revenue Recognition	Revenue Recognition The Company’s revenue has been generated primarily through collaborative research and license agreements. The terms of these agreements contain multiple deliverables, which may include (i) licenses, (ii) research and development activities, and (iii) participation in joint research and development steering committees. The terms of these agreements may include nonrefundable upfront license fees, payments for research and development activities, payments based upon the achievement of certain milestones, and royalty payments based on product sales derived from the collaboration. The Company recognizes revenue to depict the transfer of promised goods or services to customers in an amount that reflects the consideration to which the Company expects to be entitled in exchange for those goods or services. The Company receives sales-based royalties for which the license is deemed to be the predominant item to which the royalties relate and thus the Company recognizes sales-based royalties as the underlying sales are earned.
Research and Development Costs	Research and Development Costs Included in research and development costs are wages, stock-based compensation and benefits of employees performing research and development, third-party license fees and other operational costs related to the Company’s research and development activities, including facility-related expenses and external costs of outside contractors engaged to conduct both preclinical and clinical studies and manufacture quantities of product for preclinical and clinical studies. The Company expenses the cost of each contract as the work is performed. Upfront payments and milestone payments made for the licensing of technology are expensed as research and development in the period in which they are incurred. Advance payments for goods or services to be received in the future for use in research and development activities are recorded as prepaid expenses. The prepaid amounts are expensed as the related goods are delivered or the services are performed.
Research and Development and Clinical Manufacturing Accruals	Research and Development and Pharmaceutical Drug Manufacturing Accruals The Company has entered into various contracts with third parties to perform research and development and pharmaceutical drug manufacturing. This includes contracts with contract research organizations (“CROs”), clinical manufacturing organizations (“CMOs”), testing laboratories, research hospitals and not for profit organizations and other entities to support our research and development activities. When billing terms under these contracts do not coincide with the timing of when the work is performed, the Company is required to make estimates of outstanding obligations as of period end to those third parties. The accrual estimates are based on a number of factors, including the Company’s knowledge of the research and development programs and pharmaceutical drug manufacturing activities and associated timelines, invoicing to date, and the provisions in the contract. Significant judgments and estimates are made in determining the accrued balances at the end of any reporting period. Actual results could differ from our estimates.
Patent Costs	Patent Costs All patent-related costs incurred in connection with filing and prosecuting patent applications are recorded as general and administrative expenses as incurred.
Stock-Based Compensation	Stock-Based Compensation The Company measures all stock options and other stock-based awards granted to employees at fair value on the date of grant. The Company uses the Black-Scholes option-pricing model in the valuation of its stock options. The fair value of performance-based awards and restricted stock units is based on the fair value of the stock on the date of grant. The Company uses the Monte-Carlo model in order to calculate the fair value of the market-based awards. The fair value of options is recognized as stock-based compensation expense over the requisite service period, which is generally the vesting period of the respective award. The Company accounts for stock-based compensation expense related to forfeitures as the forfeitures occur. For awards with graded vesting, the straight-line method of expense recognition is applied to all awards with service-only based conditions. The Company records stock-based compensation expense related to performance-based awards when the performance-based targets are probable of being achieved. The Company classifies stock-based compensation expense in the consolidated statements of operations in the same manner in which the award recipient’s payroll costs are classified.
Income Taxes	Income Taxes The Company accounts for income taxes using the asset and liability method, which requires the recognition of deferred tax assets and liabilities for the expected future tax consequences of events that have been recognized in the financial statements or in the Company’s tax returns. Deferred taxes are determined based on the difference between the financial reporting and tax basis of assets and liabilities using enacted tax rates in effect in the years in which the differences are expected to reverse. Changes in deferred tax assets and liabilities are recorded in income tax expense. The Company assesses the likelihood that its deferred tax assets will be recovered from future taxable income and, to the extent it believes based upon the weight of available evidence, that it is more likely than not that all or a portion of deferred tax assets will not be realized, a valuation allowance is established through a charge to income tax expense. The realization of deferred tax assets is dependent upon the Company’s ability to generate future taxable income during the periods in which those temporary differences become deductible. Potential for recovery of deferred tax assets is evaluated by estimating the future taxable profits expected and considering prudent and feasible tax planning strategies. Uncertain tax positions represent tax positions for which reserves have been established. The Company accounts for uncertainty in income taxes recognized in the consolidated financial statements by applying a two-step process to determine the amount to be recognized. First, the tax position must be evaluated to determine the likelihood that it will be sustained upon external examination by the taxing authorities. If the tax position is deemed more likely than not to be sustained, the tax position is then assessed to determine the amount of benefit to be recognized in the financial statements. The amount that may be recognized is the largest amount that has a greater than 50 % likelihood of being realized upon ultimate settlement. Income tax expense includes the effects of any resulting tax reserves, or unrecognized tax benefits, that are considered appropriate as well as the related net interest and penalties.
Net Income (Loss) per Share	Net Income (Loss) per Share Basic net income (loss) per common share is computed by dividing the net income by the weighted average number of shares of common stock outstanding for the period. Diluted net income per common share is computed by dividing net income by the weighted average number of common shares outstanding for the period, including potential dilutive common shares assuming the dilutive effect of outstanding stock options and unvested restricted stock units. Market-based awards are included in diluted net income per common share to the extent they would have vested if the period end date was the market criteria measurement date. In the event the Company reports a net loss for the period, the dilutive effect of options or awards is considered anti-dilutive and disclosed accordingly.
Segment Data	Segment Data The Company manages its operations as a single segment for the purposes of assessing performance and making operating decisions. The Company is a biotechnology company focused on discovering and developing small molecule drugs for the treatment of viral infections and liver diseases. Revenue is generated exclusively from transactions occurring with partners located in the United States and all assets are held in the United States.
Comprehensive Income (Loss)	Comprehensive Income (Loss) Comprehensive income (loss) includes net income (loss) as well as other changes in stockholders’ equity that result from transactions and economic events other than those with stockholders. The Company’s only element of other comprehensive income (loss) is unrealized gains and losses on available-for-sale marketable securities.
Going Concern	Going Concern In August 2014, the Financial Accounting Standards Board (the “FASB”) issued ASU 2014-15, Presentation of Financial Statements - Going Concern (Subtopic 205-40) (“ASU 2014-15”). The Company adopted this standard as of September 30, 2017. The standard requires the Company to assess its ability to continue as a going concern one year beyond the date of filing and, in certain circumstances, provide additional footnote disclosures. Based on a detailed cash forecast incorporating current research and development activities and related spending plans, the Company believes that its current cash, cash equivalents and short-term and long-term marketable securities on hand at September 30, 2021 is sufficient to fund operations for at least the next twelve months beyond the date of issuance of these consolidated financial statements. The amount of capital available will depend on the Company’s management of its existing cash, cash equivalents and short-term and long-term marketable securities, as well as the level of future royalties the Company earns under its agreement with AbbVie. If the Company should require financing beyond these resources to fund its research and development efforts, it may not be able to obtain financing on acceptable terms, or at all.
Recently Issued Accounting Pronouncements	Recently Issued Accounting Pronouncements In June 2016, the FASB issued ASU No. 2016-13, Financial Instruments—Credit Losses (Topic 326) (“ASU 2016-13”), which introduces a new methodology for accounting for credit losses on financial instruments, including available-for-sale debt securities. The guidance establishes a new “expected loss model” that requires entities to estimate current expected credit losses on financial instruments by using all practical and relevant information. Any expected credit losses are to be reflected as allowances rather than reductions in the amortized cost of available-for-sale debt securities. The Company adopted ASU 2016-13 as of October 1, 2020. For available-for-sale debt securities with unrealized losses, the Company measures credit losses in a manner similar to previous U.S. GAAP, except that losses will be recognized as allowances instead of reductions in the amortized cost of the debt securities. The adoption of ASU 2016-13 did not have a material impact on the consolidated financial statements. The Company adopted ASU No. 2016-02, Leases (Topic 842) , as of October 1, 2019, using the modified retrospective method under ASU No. 2018-11, Leases (Topic 842): Targeted Improvements . The transition method allows entities to apply the transition requirements at the effective date rather than at the beginning of the earliest comparative period presented. The Company’s reporting for comparative periods is presented in accordance with ASC 840, Leases. Adoption of the new standard resulted in the recording of right of use (“ROU”) assets and lease liabilities of $ 7,151 and $ 8,622 , respectively. The adoption of the standard did not have a material impact on the Company’s results of operations or cash flows. The Company elected to use the transition package of three practical expedients, which among other things, allowed the Company to carry forward the historical lease classification. The Company has elected, under Topic 842, the further practical expedient not to separate non-lease components from the lease components to which they relate and instead to combine them and account for them as a single lease component. The Company also elected the accounting policy election to keep leases with a term of twelve months or less off the balance sheet and to recognize payments for those leases on a straight-line basis over the lease term. ROU assets represent the Company’s right to use an underlying asset for the lease term, and lease liabilities represent the Company’s obligation to make lease payments arising from the lease. At the inception of the arrangement, the Company determines if an arrangement is a lease based on an assessment of the terms and conditions of the contract. Operating lease ROU assets and lease liabilities are recognized at the commencement date, and thereafter, if modified, based on the present value of lease payments over the lease term. The lease term includes any renewal or early-termination options that the Company is reasonably assured to exercise. The present value of lease payments is determined by using the interest rate implicit in the lease, if that rate is readily determinable; otherwise, the Company uses its estimated secured incremental borrowing rate for that lease term. The underlying assets of the Company’s leases as of the adoption date consisted of office and laboratory space. In March 2017, the FASB issued ASU No. 2017-08, Receivables—Nonrefundable Fees and Other Costs (Subtopic 310-20): Premium Amortization on Purchased Callable Debt Securities (“ASU 2017-08”) which requires companies to amend the amortization period for premiums on debt securities with explicit call features to be the period through the earliest call date rather than through the contractual life of the debt instrument. This amendment aims to more closely align the recognition of interest income with the manner in which market participants price such instruments. The Company adopted the new standard on the effective date of October 1, 2019. The adoption of the standard did not have a material impact on the Company’s financial position and results of operations. In December 2019, the FASB issued ASU No. 2019-12, Simplifying the Accounting for Income Taxes (Topic 740), which removes certain exceptions to the general principles in Topic 740 – Income Taxes and improves consistent application of and simplifies GAAP for other areas of Topic 740 by clarifying and amending existing guidance. This ASU is effective for the Company beginning October 1, 2021 and interim periods within that year, with early adoption permitted. The Company does not expect the adoption of the standard to have a material impact on the Company's financial position or results of operations.

Summary of Significant Accoun_3

Summary of Significant Accounting Policies (Tables)	12 Months Ended
	Sep. 30, 2021
Accounting Policies [Abstract]
Property and Equipment Estimated Useful Lives	Property and equipment are stated at cost less accumulated depreciation. Depreciation expense is recognized using the straight-line method over the following estimated useful lives: Laboratory and office equipment 5 years Leasehold improvements Shorter of life of lease or estimated useful life Purchased software 3 years Computer equipment 3 years Furniture 7 years

Fair Value of Financial Asset_2

Fair Value of Financial Assets and Liabilities (Tables)	12 Months Ended
	Sep. 30, 2021
Fair Value Disclosures [Abstract]
Financial Assets and Liabilities that were Subject to Fair Value Measurement on Recurring Basis	The following tables present information about the Company’s financial assets and liabilities that were subject to fair value measurement on a recurring basis as of September 30, 2021 and 2020 and indicate the fair value hierarchy of the valuation inputs utilized to determine such fair value: Fair Value Measurements at September 30, 2021 Using: Level 1 Level 2 Level 3 Total (in thousands) Assets: Cash equivalents: Money market funds $ 54,819 $ — $ — $ 54,819 Marketable securities: U.S. Treasury notes 83,038 — — 83,038 Corporate bonds — 124,703 — 124,703 Commercial paper — 87,471 — 87,471 $ 137,857 $ 212,174 $ — $ 350,031 Liabilities: Series 1 nonconvertible preferred stock — — 1,506 1,506 $ — $ — $ 1,506 $ 1,506 Fair Value Measurements at September 30, 2020 Using: Level 1 Level 2 Level 3 Total (in thousands) Assets: Cash equivalents: Money market funds $ 81,502 $ — $ — $ 81,502 Marketable securities: U.S. Treasury notes 94,208 — — 94,208 Commercial paper — 93,909 — 93,909 Corporate bonds — 144,035 — 144,035 $ 175,710 $ 237,944 $ — $ 413,654 Liabilities: Series 1 nonconvertible preferred stock — — 1,479 1,479 $ — $ — $ 1,479 $ 1,479
Fair Value Measurements of the Company's Series 1 Nonconvertible Preferred Stock	The recurring Level 3 fair value measurements of the Company’s Series 1 nonconvertible preferred stock using probability-weighted discounted cash flow include the following significant unobservable inputs: Range September 30, Unobservable Input 2021 2020 Probabilities of payout 0 %- 65 % 0 %- 60 % Discount rate 4.2 5% 4.25 %
Rollforward of Aggregate Fair Value of Company's Outstanding Series 1 Nonconvertible Preferred Stock	The following table provides a rollforward of the aggregate fair value of the Company’s outstanding Series 1 nonconvertible preferred stock for which fair value is determined by Level 3 inputs: Series 1 (in thousands) Balance, September 30, 2018 $ 1,628 No change in fair value — Balance, September 30, 2019 1,628 Decrease in fair value ( 149 ) Balance, September 30, 2020 1,479 Increase in fair value 27 Balance, September 30, 2021 $ 1,506

Marketable Securities (Tables)

Marketable Securities (Tables)	12 Months Ended
	Sep. 30, 2021
Investments Debt And Equity Securities [Abstract]
Fair Value of Available-for-Sale Marketable Securities by Type of Security	As of September 30, 2021 and 2020, the fair value of available-for-sale marketable securities, by type of security, was as follows: September 30, 2021 Amortized Gross Gross Credit Losses Fair Value (in thousands) Corporate bonds $ 124,678 $ 93 $ ( 68 ) $ — $ 124,703 Commercial paper 87,471 — — — 87,471 U.S. Treasury notes 83,061 3 ( 26 ) — 83,038 $ 295,210 $ 96 $ ( 94 ) $ — $ 295,212 September 30, 2020 Amortized Gross Gross Credit Losses Fair Value (in thousands) Corporate bonds $ 143,274 $ 775 $ ( 14 ) $ — $ 144,035 Commercial paper 93,909 — — — 93,909 U.S. Treasury notes 93,740 468 — — 94,208 $ 330,923 $ 1,243 $ ( 14 ) $ — $ 332,152

Property and Equipment, Net (Ta

Property and Equipment, Net (Tables)	12 Months Ended
	Sep. 30, 2021
Property Plant And Equipment [Abstract]
Schedule of Property and Equipment, Net	Property and equipment, net consisted of the following as of September 30, 2021 and 2020: September 30, 2021 2020 (in thousands) Laboratory and office equipment $ 14,499 $ 14,036 Leasehold improvements 7,140 7,089 Purchased software 1,387 1,364 Furniture 1,294 1,276 Computer equipment 529 505 Construction in progress 20 — 24,869 24,270 Less: Accumulated depreciation and amortization ( 18,926 ) ( 15,674 ) $ 5,943 $ 8,596

Accrued Expenses and Other Cu_2

Accrued Expenses and Other Current Liabilities and Other Long-Term Liabilities (Tables)	12 Months Ended
	Sep. 30, 2021
Payables And Accruals [Abstract]
Accrued Expenses and Other Current Liabilities and Other Long-Term Liabilities	Accrued expenses and other current liabilities and other long-term liabilities consisted of the following as of September 30, 2021 and 2020: September 30, 2021 2020 Accrued expenses and other current liabilities: (in thousands) Accrued research and development expenses $ 6,062 $ 5,407 Accrued payroll and related expenses 6,094 4,777 Accrued pharmaceutical drug manufacturing 8,402 2,885 Accrued professional fees 700 478 Accrued other 1,171 612 $ 22,429 $ 14,159 Other long-term liabilities: Uncertain tax positions $ 558 $ 788 Asset retirement obligation — 290 $ 558 $ 1,078

Collaboration Agreements (Table

Collaboration Agreements (Tables)	12 Months Ended
	Sep. 30, 2021
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Summary of Royalty Tiers Associated with Cumulative Calendar Year Net Sales Allocated to Each Royalty-bearing Product	The following table details the royalty tiers associated with cumulative calendar year net sales allocated to each royalty-bearing product as provided in the AbbVie Agreement: Calendar Year Net Sales Royalty Tier (in thousands) (%) up to $ 500,000 10 % from $ 500,000 up to $ 750,000 12 % from $ 750,000 up to $ 1,000,000 14 % from $ 1,000,000 up to $ 2,500,000 17 % greater than or equal to $ 2,500,000 20 %

Stock-Based Awards (Tables)

Stock-Based Awards (Tables)	12 Months Ended
	Sep. 30, 2021
Data Used to Determine Value of Stock Option Grants, Presented on Weighted Average Basis	The relevant data used to determine the value of the stock option awards are as follows, presented on a weighted average basis: Years Ended September 30, 2021 2020 2019 Risk-free interest rate 0.61 % 1.41 % 2.76 % Expected term (in years) 6.05 6.02 6.05 Expected volatility 52 % 53 % 55 % Expected dividends 0 % 0 % 0 % Weighted average grant date fair value $ 21.76 $ 30.47 $ 44.66
Summary of Stock Option Activity Including Performance Based Options	The following table summarizes stock option activity, including aggregate intrinsic value for the year ended September 30, 2021: Shares Weighted Weighted Aggregate (in thousands) (in thousands) Outstanding as of September 30, 2020 3,262 $ 49.82 6.5 $ 21,860 Granted 901 45.01 Exercised ( 129 ) 27.99 Forfeited ( 182 ) 67.01 Outstanding as of September 30, 2021 3,852 $ 48.61 6.4 $ 49,173 Options vested and expected to vest as of September 30, 2021 3,852 $ 48.61 6.4 $ 49,173 Options exercisable as of September 30, 2021 2,520 $ 45.91 5.2 $ 39,356
Summary of Additional Exercise and Grant Date Information	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. The following tables summarize additional exercise and grant date information: Years Ended September 30, 2021 2020 2019 (in thousands) Aggregate intrinsic value of stock options exercised $ 2,704 $ 7,850 $ 13,855 Proceeds to Company from stock options exercised $ 3,614 $ 10,481 $ 6,848
Summary of Restricted Stock Unit Activity	The following table summarizes the restricted stock unit activity for the year to date period ending September 30, 2021: Restricted Weighted (in thousands, except per share data) Unvested at September 30, 2020 45 $ 30.00 Granted 123 43.57 Vested ( 45 ) 30.00 Cancelled ( 6 ) 41.40 Unvested at September 30, 2021 117 $ 43.57
Stock-Based Compensation Expense	The Company recorded the following stock-based compensation expense for the years ended September 30, 2021, 2020, and 2019: Years Ended September 30, 2021 2020 2019 (in thousands) Research and development $ 10,075 $ 10,096 $ 8,833 General and administrative 10,916 9,479 10,393 $ 20,991 $ 19,575 $ 19,226 Years Ended September 30, 2021 2020 2019 (in thousands) Stock options $ 18,004 $ 17,459 $ 15,854 rTSRUs 1,537 1,216 1,568 PSUs 235 259 1,278 Restricted stock units 1,215 641 526 $ 20,991 $ 19,575 $ 19,226
Relative Total Stockholder Return Units [Member]
Data Used to Determine Value of Stock Option Grants, Presented on Weighted Average Basis	The table below sets forth the weighted average grant date fair value assumptions used to value the rTSRUs: Years Ended September 30, 2021 2020 2019 Risk-free interest rate 0.13 % 1.62 % 2.65 % Dividend yield 0 % 0 % 0 % Expected volatility 74 % 68 % 62 % Remaining performance period (years) 1.97 2.03 2.03
Performance Share Units and Relative Total Stockholder Return Units [Member]
Summary of PSUs and rTSRUs Activity	The following table summarizes PSU and rTSRU activity (at target) for the year ended September 30, 2021: PSUs rTSRUs Shares Weighted Shares Weighted (in thousands, except per share data) Unvested at September 30, 2020 46 $ 65.23 46 $ 46.46 Granted 84 44.58 84 26.55 Vested — — — — Cancelled ( 19 ) 67.13 ( 19 ) 47.42 Unvested at September 30, 2021 111 $ 49.31 111 $ 31.26

Net Income (Loss) Per Share (Ta

Net Income (Loss) Per Share (Tables)	12 Months Ended
	Sep. 30, 2021
Earnings Per Share [Abstract]
Basic and Diluted Net Income (Loss) Per Common Share	Basic and diluted net income (loss) per common share was calculated as follows for the years ended September 30, 2021, 2020, and 2019: Years Ended September 30, 2021 2020 2019 (in thousands, except per share data) Basic net income (loss) per share: Numerator: Net income (loss) $ ( 78,996 ) $ ( 36,168 ) $ 46,383 Denominator: Weighted average common shares outstanding — basic 20,171 19,940 19,584 Net income (loss) per share common share — basic $ ( 3.92 ) $ ( 1.81 ) $ 2.37 Diluted net income (loss) per share: Numerator: Net income (loss) $ ( 78,996 ) $ ( 36,168 ) $ 46,383 Denominator: Weighted average common shares outstanding — basic 20,171 19,940 19,584 Dilutive effect of common stock equivalents — — 1,384 Weighted average common shares outstanding — diluted 20,171 19,940 20,968 Net income (loss) per share common share — diluted $ ( 3.92 ) $ ( 1.81 ) $ 2.21 Anti-dilutive common stock equivalents excluded from above 4,297 3,502 843

Leases (Tables)

Leases (Tables)	12 Months Ended
	Sep. 30, 2021
Leases [Abstract]
Components of Lease Expense for Real Estate and Equipment Leases and Other Information Related to Leases	The components of lease expense for the Company’s real estate and equipment leases were as follows: Years Ended September 30, 2021 2020 (in thousands) Operating lease cost $ 5,861 $ 3,776 Short-term lease cost — — Variable lease cost 4,057 2,338 $ 9,918 $ 6,114 Years Ended September 30, 2021 2020 (in thousands) Cash paid for amounts included in the measurement of operating lease liabilities $ 6,364 $ 4,126 Operating lease liabilities arising from obtaining right-of-use assets $ 3,320 $ 3,053 September 30, 2021 2020 Weighted-average remaining lease term - operating leases (in years) 1.43 2.20 Weighted-average discount rate - operating leases 6.08 % 6.50 %
Schedule of Future Annual Minimum Lease Payments	Future annual minimum lease payments under the Company’s real estate and equipment operating leases as of September 30, 2021 were as follows: Years ended September 30, (in thousands) 2022 4,391 2023 675 2024 519 2025 — 2026 — Total future minimum lease payments 5,585 Less: Imputed interest ( 256 ) Total operating lease liabilities $ 5,329
Schedule of Lease Included in Balance Sheet	Included in the balance sheet: 2021 2020 (in thousands) Current operating lease liabilities $ 4,203 $ 4,261 Operating lease liabilities, net of current portion 1,126 3,838 Total operating lease liabilities $ 5,329 $ 8,099

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Sep. 30, 2021
Income Tax Disclosure [Abstract]
Summary of Income Tax Benefit (Expense)	During the years ended September 30, 2021, 2020, and 2019, the Company recorded income tax benefit (expense) as follows: Years Ended September 30, 2021 2020 2019 (in thousands) Current income tax benefit (expense): Federal $ 28,721 $ 8,491 $ ( 1,841 ) State 205 941 ( 372 ) Deferred income tax benefit (expense): Federal ( 343 ) ( 8,916 ) 2,431 State — ( 1,665 ) 608 Income tax (expense) benefit $ 28,583 $ ( 1,149 ) $ 826
Reconciliation of Income Tax Provision at Federal Statutory Income Tax Rate and Effective Tax Rate	A reconciliation of the U.S. federal statutory income tax rate to the Company’s effective tax rate is as follows: Years Ended September 30, 2021 2020 2019 Federal statutory income tax rate ( 21.0 %) ( 21.0 %) 21.0 % State taxes, net of federal benefit ( 2.3 ) ( 2.8 ) 1.8 Change in valuation allowance 9.9 52.1 — Federal research and development tax credit ( 5.3 ) ( 13.3 ) ( 12.8 ) Share-based compensation 2.4 2.8 ( 6.7 ) Change in deferred tax rate ( 9.5 ) ( 10.2 ) — Foreign-derived intangible income — — ( 3.2 ) Other ( 0.8 ) ( 4.3 ) ( 1.9 ) Effective income tax rate ( 26.6 %) 3.3 % ( 1.8 %)
Changes in the Valuation Allowance for Deferred Tax Assets	Changes in the valuation allowance for deferred tax assets during the years ended September 30, 2021, 2020, and 2019 are as follows: Years Ended September 30, 2021 2020 2019 (in thousands) Valuation allowance, beginning of year $ ( 18,259 ) $ — $ — Increase recorded to valuation allowance ( 11,039 ) — — Initial recording of valuation allowance — ( 18,259 ) — Valuation allowance, end of year $ ( 29,298 ) $ ( 18,259 ) $ —
Net Deferred Tax Assets and Liabilities	Net deferred tax assets as of September 30, 2021 and 2020 consisted of the following: September 30, 2021 2020 (in thousands) Deferred tax assets: Share-based compensation $ 11,843 $ 11,071 Tax credit carryforwards 13,170 6,574 Operating lease liability 1,232 2,468 Accrued compensation 1,284 1,598 Net operating loss carryforward 3,095 861 Accrued expenses 378 245 Other temporary differences 366 444 Total deferred tax assets 31,368 23,261 Valuation allowance ( 29,298 ) ( 18,259 ) Net deferred tax assets 2,070 5,002 Deferred tax liabilities: Right of use asset ( 1,110 ) ( 2,221 ) Depreciation ( 684 ) ( 1,650 ) Prepaid expenses ( 275 ) ( 364 ) Unrealized loss ( 1 ) ( 422 ) Total deferred tax liabilities ( 2,070 ) ( 4,657 ) Net deferred income tax assets (liabilities) $ — $ 345
Schedule of Reconciliation of Uncertain Tax Positions	A reconciliation of the beginning and ending amount of uncertain tax positions is summarized as follows: September 30, 2021 2020 (in thousands) Beginning Balance $ 844 $ 1,650 Additions based on tax positions for the current period 10 11 Reductions for tax positions due to lapse of statute of limitations ( 134 ) ( 719 ) Reductions for tax positions of prior periods ( 98 ) ( 98 ) Ending Balance $ 622 $ 844

Subsequent Events (Tables)

Subsequent Events (Tables)	12 Months Ended
	Sep. 30, 2021
Subsequent Events [Abstract]
Schedule of Subsequent Events	The updated minimum lease payments related to the 500 Arsenal Street lease as a result of the extension are as follows: Years ended September 30, (in thousands) 2022 2,487 2023 3,502 2024 3,607 2025 3,715 2026 3,827 Thereafter 3,604 Total future minimum lease payments $ 20,742

Nature of the Business - Additi

Nature of the Business - Additional Information (Detail)	12 Months Ended
	Sep. 30, 2021
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Entity incorporated, in year	1995

Summary of Significant Accoun_4

Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($)	12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019	Oct. 01, 2019
Summary of Accounting and Financial Policies [Line Items]
Adjustment to fair value	$ 0	$ 0	$ 0
Cash and investment restricted as a collateral for outstanding letter of credit	608,000	608,000
Operating lease, right-of-use assets	4,711,000	7,020,000		$ 8,622,000
Total operating lease liabilities	5,329,000	8,099,000		$ 7,151,000
Money Market Funds [Member]
Summary of Accounting and Financial Policies [Line Items]
Cash and investment restricted as a collateral for outstanding letter of credit	$ 608,000	$ 608,000
Maximum [Member]
Summary of Accounting and Financial Policies [Line Items]
Short-term investments maturity period	90 days
Short-term marketable securities maturity period	1 year
Minimum [Member]
Summary of Accounting and Financial Policies [Line Items]
Short-term marketable securities maturity period	90 days
Long-term marketable securities maturity period	1 year
Income tax benefit recognition, percentage of likelihood of being realized upon settlement	50.00%

Summary of Significant Accoun_5

Summary of Significant Accounting Policies - Property and Equipment Estimated Useful Lives (Detail)	12 Months Ended
	Sep. 30, 2021
Laboratory and Office Equipment [Member]
Property, Plant and Equipment [Line Items]
Property plant and equipment useful life	5 years
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Leasehold improvements useful life	Shorter of life of lease or estimated useful life
Purchased Software [Member]
Property, Plant and Equipment [Line Items]
Property plant and equipment useful life	3 years
Computer Equipment [Member]
Property, Plant and Equipment [Line Items]
Property plant and equipment useful life	3 years
Furniture [Member]
Property, Plant and Equipment [Line Items]
Property plant and equipment useful life	7 years

Fair Value of Financial Asset_3

Fair Value of Financial Assets and Liabilities - Financial Assets and Liabilities that were Subject to Fair Value Measurement on Recurring Basis (Detail) - USD ($) $ in Thousands	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Assets:
Marketable securities	$ 295,212	$ 332,152
Assets, Fair Value Disclosure, Total	350,031	413,654
Liabilities:
Liabilities, Fair Value Disclosure, Total	1,506	1,479
Series 1 Nonconvertible Preferred Stock [Member]
Liabilities:
Liabilities	1,506	1,479	$ 1,628	$ 1,628
Level 1 [Member]
Assets:
Assets, Fair Value Disclosure, Total	137,857	175,710
Level 2 [Member]
Assets:
Assets, Fair Value Disclosure, Total	212,174	237,944
Level 3 [Member]
Liabilities:
Liabilities, Fair Value Disclosure, Total	1,506	1,479
Level 3 [Member] | Series 1 Nonconvertible Preferred Stock [Member]
Liabilities:
Liabilities	1,506	1,479
U.S. Treasury Notes [Member]
Assets:
Marketable securities	83,038	94,208
U.S. Treasury Notes [Member] | Level 1 [Member]
Assets:
Marketable securities	83,038	94,208
Money Market Funds [Member]
Assets:
Cash equivalents	54,819	81,502
Money Market Funds [Member] | Level 1 [Member]
Assets:
Cash equivalents	54,819	81,502
Commercial Paper [Member]
Assets:
Marketable securities	87,471	93,909
Commercial Paper [Member] | Level 2 [Member]
Assets:
Marketable securities	87,471	93,909
Corporate Bonds [Member]
Assets:
Marketable securities	124,703	144,035
Corporate Bonds [Member] | Level 2 [Member]
Assets:
Marketable securities	$ 124,703	$ 144,035

Fair Value of Financial Asset_4

Fair Value of Financial Assets and Liabilities - Additional Information (Detail) - USD ($)	12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019
Fair Value Disclosures [Abstract]
Transfers between Level 1, Level 2 and Level 3	$ 0	$ 0	$ 0

Fair Value of Financial Asset_5

Fair Value of Financial Assets and Liabilities - Fair Value Measurements of the Company's Series 1 Nonconvertible Preferred Stock (Detail) - Level 3 [Member] - Series 1 Nonconvertible Preferred Stock [Member]	Sep. 30, 2021	Sep. 30, 2020
Probabilities of Payout [Member] | Minimum [Member]
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Range	0	0
Probabilities of Payout [Member] | Maximum [Member]
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Range	0.65	0.60
Discount Rate [Member]
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Range	0.042	0.0425

Fair Value of Financial Asset_6

Fair Value of Financial Assets and Liabilities - Rollforward of Aggregate Fair Value of Company's Outstanding Series 1 Nonconvertible Preferred Stock (Detail) - Series 1 Nonconvertible Preferred Stock [Member] - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning Balance	$ 1,479	$ 1,628	$ 1,628
Increase (Decrease) in fair value	27	(149)	0
Ending Balance	$ 1,506	$ 1,479	$ 1,628

Marketable Securities - Fair Va

Marketable Securities - Fair Value of Available-for-Sale Marketable Securities by Type of Security (Detail) - USD ($) $ in Thousands	Sep. 30, 2021	Sep. 30, 2020
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 295,210	$ 330,923
Gross Unrealized Gains	96	1,243
Gross Unrealized Losses	(94)	(14)
Fair value	295,212	332,152
Corporate Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	124,678	143,274
Gross Unrealized Gains	93	775
Gross Unrealized Losses	(68)	(14)
Fair value	124,703	144,035
Commercial Paper [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	87,471	93,909
Fair value	87,471	93,909
U.S. Treasury Notes [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	83,061	93,740
Gross Unrealized Gains	3	468
Gross Unrealized Losses	(26)
Fair value	$ 83,038	$ 94,208

Marketable Securities - Additio

Marketable Securities - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Schedule of Available-for-sale Securities [Line Items]
Long-term marketable securities	$ 108,416	$ 32,634
Short Term Marketable Securities [Member] | Maximum [Member]
Schedule of Available-for-sale Securities [Line Items]
Maturity period of the marketable securities	1 year
Corporate Bonds and U.S. Treasury Notes [Member] | Long Term Marketable Securities [Member] | Maximum [Member]
Schedule of Available-for-sale Securities [Line Items]
Maturity period of the marketable securities	3 years
Corporate Bonds and U.S. Treasury Notes [Member] | Long Term Marketable Securities [Member] | Minimum [Member]
Schedule of Available-for-sale Securities [Line Items]
Maturity period of the marketable securities	1 year

Property and Equipment, Net - S

Property and Equipment, Net - Schedule of Property and Equipment, Net (Detail) - USD ($) $ in Thousands	Sep. 30, 2021	Sep. 30, 2020
Property, Plant and Equipment [Line Items]
Property and equipment	$ 24,869	$ 24,270
Less: Accumulated depreciation and amortization	(18,926)	(15,674)
Property and equipment, net	5,943	8,596
Laboratory and Office Equipment [Member]
Property, Plant and Equipment [Line Items]
Property and equipment	14,499	14,036
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Property and equipment	7,140	7,089
Purchased Software [Member]
Property, Plant and Equipment [Line Items]
Property and equipment	1,387	1,364
Furniture [Member]
Property, Plant and Equipment [Line Items]
Property and equipment	1,294	1,276
Computer Equipment [Member]
Property, Plant and Equipment [Line Items]
Property and equipment	529	$ 505
Construction in Progress [Member]
Property, Plant and Equipment [Line Items]
Property and equipment	$ 20

Property and Equipment, Net - A

Property and Equipment, Net - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019
Property Plant And Equipment [Line Items]
Depreciation and amortization expense	$ 3,334	$ 3,644	$ 3,258
Property, Plant and Equipment [Member]
Property Plant And Equipment [Line Items]
Depreciation and amortization expense	$ 3,334	$ 3,644	$ 3,258

Accrued Expenses and Other Cu_3

Accrued Expenses and Other Current Liabilities and Other Long-Term Liabilities - Accrued Expenses and Other Current Liabilities and Other Long-term Liabilities (Detail) - USD ($) $ in Thousands	Sep. 30, 2021	Sep. 30, 2020
Accrued expenses and other current liabilities:
Accrued research and development expenses	$ 6,062	$ 5,407
Accrued payroll and related expenses	6,094	4,777
Accrued pharmaceutical drug manufacturing	8,402	2,885
Accrued professional fees	700	478
Accrued other	1,171	612
Accrued expenses	22,429	14,159
Other long-term liabilities:
Uncertain tax positions	558	788
Asset retirement obligation		290
Other long-term liabilities	$ 558	$ 1,078

Collaboration Agreements - Addi

Collaboration Agreements - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Milestone revenue payments received	$ 97,074	$ 122,473	$ 205,197
AbbVie [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaboration agreement date	Nov. 27, 2006
Proceed received to fund research activities and preferred stock financing	$ 396,000
Collaboration agreement tiered royalty description	from ten percent up to twenty percent, or on a blended basis from the low double digits up to the high teens, on the portion of AbbVie’s calendar year net sales
Agreement continuation period	10 years

Collaboration Agreements - Summ

Collaboration Agreements - Summary of Royalty Tiers Associated with Cumulative Calendar Year Net Sales Allocated to Each Royalty-bearing Product (Detail) - AbbVie [Member] $ in Thousands	12 Months Ended
	Sep. 30, 2021USD ($)
Scenario One [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Royalty Tier	10.00%
Scenario One [Member] | Maximum [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Calendar Year Net Sales	$ 500,000
Scenario Two [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Royalty Tier	12.00%
Scenario Two [Member] | Minimum [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Calendar Year Net Sales	$ 500,000
Scenario Two [Member] | Maximum [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Calendar Year Net Sales	$ 750,000
Scenario Three [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Royalty Tier	14.00%
Scenario Three [Member] | Minimum [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Calendar Year Net Sales	$ 750,000
Scenario Three [Member] | Maximum [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Calendar Year Net Sales	$ 1,000,000
Scenario Four [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Royalty Tier	17.00%
Scenario Four [Member] | Minimum [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Calendar Year Net Sales	$ 1,000,000
Scenario Four [Member] | Maximum [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Calendar Year Net Sales	2,500,000
Scenario Five [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Calendar Year Net Sales	$ 2,500,000
Royalty Tier	20.00%

Stockholders' Equity - Addition

Stockholders' Equity - Additional Information (Detail) - $ / shares shares in Thousands	Sep. 30, 2021	Sep. 30, 2020
Class Of Stock [Line Items]
Common stock, shares authorized	100,000	100,000
Common stock, par value	$ 0.01	$ 0.01
Preferred stock, shares authorized	5,000
Preferred stock, par value per share	$ 0.01
Shares are undesignated and unissued	3,000
Series 1 Nonconvertible Preferred Stock [Member]
Class Of Stock [Line Items]
Preferred stock, shares authorized	2,000
Preferred stock, par value per share	$ 0.01
Preferred stock, shares issued	2,000

Series 1 Nonconvertible Prefe_2

Series 1 Nonconvertible Preferred Stock and Warrants - Additional Information (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019	Nov. 30, 2010
Class Of Stock [Line Items]
Preferred stock, shares authorized	5,000
Preferred stock, par value per share	$ 0.01
Fair value of the Series 1 nonconvertible preferred stock	$ 1,506	$ 1,479
Series 1 Nonconvertible Preferred Stock [Member]
Class Of Stock [Line Items]
Preferred stock, shares authorized	2,000
Preferred stock, par value per share	$ 0.01
Per share value adjusted for stock dividend	1
Preferred stock redemption price per share	$ 1
Redemption period	60 days
Number of shares issuable upon exercise of the warrants				2,000
Warrant expiration date	Oct. 4, 2017
Preferred stock, shares outstanding	1,930	1,930
Change in fair value of warrants	$ (27)	$ 149	$ 0
Fair value of the Series 1 nonconvertible preferred stock	$ 1,506	$ 1,479

Stock-Based Awards - Additional

Stock-Based Awards - Additional Information (Detail) - USD ($) shares in Thousands, $ in Thousands	1 Months Ended	12 Months Ended
	Nov. 30, 2016	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares remained available for future awards under the 2019 Plan		1,093
Expected dividend yield		0.00%	0.00%	0.00%
Aggregate of unrecognized stock-based compensation cost		$ 42,222
Weighted average recognition period		2 years 3 months 18 days
Common Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Aggregate of target share issued			23	125
PSUs [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of target shares vested			15.00%	80.00%
Relative Total Stockholder Return Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of target shares vested			90.00%	200.00%
PSUs and rTSRUs [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total fair value, vested during period		$ 0	$ 1,227	$ 11,074
Restricted Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total fair value, vested during period		$ 1,897	$ 3,149	$ 0
Restricted Stock Units [Member] | Tranche One [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting percentage	50.00%
Restricted Stock Units [Member] | Tranche Two [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting percentage	50.00%
Certain Executives [Member] | PSUs [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options granted, requisite service period		2 years
Executive Officers [Member] | Relative Total Stockholder Return Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares range percentage		0.00%
Number of shares range percentage		150.00%
Employee Stock Purchase Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares available for future grant		186
Shares issued		0
2019 Equity Incentive Plan [Member] | Employees [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options granted, requisite service period		4 years
Options granted, expiration period		10 years
2019 Equity Incentive Plan [Member] | Employees [Member] | Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period		4 years
2019 Equity Incentive Plan [Member] | Non-Employee Directors [Member] | Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period		1 year

Stock-Based Awards - Data Used

Stock-Based Awards - Data Used to Determine Value of Stock Option Grants, Presented on Weighted Average Basis (Detail) - $ / shares	12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019
Share Based Payment Award Stock Options Valuation Assumptions [Line Items]
Risk-free interest rate	0.61%	1.41%	2.76%
Expected term (in years)	6 years 18 days	6 years 7 days	6 years 18 days
Expected volatility	52.00%	53.00%	55.00%
Expected dividends	0.00%	0.00%	0.00%
Weighted average grant date fair value	$ 21.76	$ 30.47	$ 44.66
Executive Officer [Member] | Relative Total Stockholder Return Units [Member]
Share Based Payment Award Stock Options Valuation Assumptions [Line Items]
Expected term (in years)	1 year 11 months 19 days	2 years 10 days	2 years 10 days
Expected volatility	74.00%	68.00%	62.00%
Risk-free interest rate	0.13%	1.62%	2.65%
Dividend yield	0.00%	0.00%	0.00%

Stock-Based Awards - Summary of

Stock-Based Awards - Summary of Stock Option Activity Including Performance Based Options (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019
Options
Outstanding as of beginning of period	3,262
Granted	901
Exercised	(129)
Forfeited	(182)
Outstanding as of end of period	3,852	3,262
Options vested and expected to vest as of end of period	3,852
Options exercisable as of end of period	2,520
Weighted Average Exercise Price
Outstanding	$ 49.82
Granted	45.01
Exercised	27.99
Forfeited	67.01
Outstanding	48.61	$ 49.82
Options vested and expected to vest as of end of period	48.61
Options exercisable as of end of period	$ 45.91
Weighted Average Remaining Contractual Term
Outstanding as of end of period	6 years 4 months 24 days	6 years 6 months
Options vested and expected to vest as of end period	6 years 4 months 24 days
Options exercisable as of end of period	5 years 2 months 12 days
Aggregate intrinsic value of stock options exercised	$ 2,704	$ 7,850	$ 13,855
Proceeds to Company from stock options exercised	$ 3,614	$ 10,481	$ 6,848

Stock-Based Awards - Summary _2

Stock-Based Awards - Summary of Stock Option Activity Including Performance Based Options - Stock Option Activity (Detail) - USD ($) $ in Thousands	Sep. 30, 2021	Sep. 30, 2020
Aggregate Intrinsic Value
Aggregate Intrinsic Value	$ 49,173	$ 21,860
Options vested and expected to vest as of end of period	49,173
Options exercisable as of end of period	$ 39,356

Stock-Based Awards - Summary _3

Stock-Based Awards - Summary of PSUs and rTSRUs Activity (Detail) shares in Thousands	12 Months Ended
	Sep. 30, 2021$ / sharesshares
PSUs [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unvested, beginning balance | shares	46
Granted | shares	84
Cancelled | shares	(19)
Unvested, ending balance | shares	111
Weighted Average Grant Date Fair Value Per Share, Unvested beginning balance | $ / shares	$ 65.23
Weighted Average Grant Date Fair Value Per Share, Granted | $ / shares	44.58
Weighted Average Grant Date Fair Value Per Share, Cancelled | $ / shares	67.13
Weighted Average Grant Date Fair Value Per Share, Unvested ending balance | $ / shares	$ 49.31
rTSRUs [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unvested, beginning balance | shares	46
Granted | shares	84
Cancelled | shares	(19)
Unvested, ending balance | shares	111
Weighted Average Grant Date Fair Value Per Share, Unvested beginning balance | $ / shares	$ 46.46
Weighted Average Grant Date Fair Value Per Share, Granted | $ / shares	26.55
Weighted Average Grant Date Fair Value Per Share, Cancelled | $ / shares	47.42
Weighted Average Grant Date Fair Value Per Share, Unvested ending balance | $ / shares	$ 31.26

Stock-Based Awards - Summary _4

Stock-Based Awards - Summary of Restricted Stock Unit Activity (Detail) - Restricted Stock Units [Member] shares in Thousands	12 Months Ended
	Sep. 30, 2021$ / sharesshares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unvested, beginning balance | shares	45
Granted | shares	123
Vested | shares	(45)
Cancelled | shares	(6)
Unvested, ending balance | shares	117
Weighted Average Grant Date Fair Value Per Share, Unvested beginning balance | $ / shares	$ 30
Weighted Average Grant Date Fair Value Per Share, Granted | $ / shares	43.57
Weighted Average Grant Date Fair Value Per Share, Vested | $ / shares	30
Weighted Average Grant Date Fair Value Per Share, Cancelled | $ / shares	41.40
Weighted Average Grant Date Fair Value Per Share, Unvested ending balance | $ / shares	$ 43.57

Stock-Based Awards - Stock-Base

Stock-Based Awards - Stock-Based Compensation Expense (Detail) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	$ 20,991	$ 19,575	$ 19,226
Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	18,004	17,459	15,854
PSUs [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	235	259	1,278
rTSRUs [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	1,537	1,216	1,568
Restricted Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	1,215	641	526
Research and Development [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	10,075	10,096	8,833
General and Administrative [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	$ 10,916	$ 9,479	$ 10,393

Net Income (Loss) Per Share - B

Net Income (Loss) Per Share - Basic and Diluted Net Income (Loss) Per Common Share (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019
Basic net income (loss) per share:
Net income (loss)	$ (78,996)	$ (36,168)	$ 46,383
Weighted average common shares outstanding — basic	20,171	19,940	19,584
Net income (loss) per share common share -basic	$ (3.92)	$ (1.81)	$ 2.37
Diluted net income (loss) per share:
Net income (loss)	$ (78,996)	$ (36,168)	$ 46,383
Basic	20,171	19,940	19,584
Dilutive effect of common stock equivalents			1,384
Weighted average common shares outstanding — diluted	20,171	19,940	20,968
Net income (loss) per share common share — diluted	$ (3.92)	$ (1.81)	$ 2.21
Anti-dilutive common stock equivalents excluded from above	4,297	3,502	843

Leases - Additional Information

Leases - Additional Information (Detail) $ in Thousands	12 Months Ended
	Sep. 30, 2021USD ($)Lease	Sep. 30, 2020USD ($)	Oct. 31, 2019
Lessee Lease Description [Line Items]
Number of Leases | Lease	2
Lease option to extend	two options to extend the lease term for an additional three years each.
Lease periods commencing upon shipment			18 months
Outstanding letter of credit	$ 608	$ 608
Cash and investment restricted as a collateral for outstanding letter of credit	$ 608	$ 608
First Lease [Member] | 500 Arsenal Street, Watertown, Massachusetts [Member]
Lessee Lease Description [Line Items]
Office lease expiration period	2022-09
Lease option to extend	an option to extend the lease term for an additional five years.
Second Lease [Member] | 400 Talcott Avenue, Watertown, Massachusetts [Member]
Lessee Lease Description [Line Items]
Office lease expiration period	2024-08
Period of lease agreement	2018-09

Leases - Components of Lease Ex

Leases - Components of Lease Expense for Real Estate and Equipment Leases and Other Information Related to Leases (Detail) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Leases [Abstract]
Operating lease cost	$ 5,861	$ 3,776
Short-term lease cost	0	0
Variable lease cost	4,057	2,338
Lease, cost	9,918	6,114
Cash paid for amounts included in the measurement of operating lease liabilities	6,364	4,126
Operating lease liabilities arising from obtaining right-of-use assets	$ 3,320	$ 3,053
Weighted-average remaining lease term - operating leases (in years)	1 year 5 months 4 days	2 years 2 months 12 days
Weighted-average discount rate - operating leases	6.08%	6.50%

Leases - Schedule of Future Ann

Leases - Schedule of Future Annual Minimum Lease Payments (Detail) - USD ($) $ in Thousands	Sep. 30, 2021	Sep. 30, 2020	Oct. 01, 2019
Leases [Abstract]
2022	$ 4,391
2023	675
2024	519
2025	0
2026	0
Total future minimum lease payments	5,585
Less: Imputed interest	(256)
Total operating lease liabilities	$ 5,329	$ 8,099	$ 7,151

Leases - Schedule of Lease Incl

Leases - Schedule of Lease Included in Balance Sheet (Detail) - USD ($) $ in Thousands	Sep. 30, 2021	Sep. 30, 2020	Oct. 01, 2019
Leases [Abstract]
Operating lease liabilities	$ 4,203	$ 4,261
Operating lease liabilities, net of current portion	1,126	3,838
Total operating lease liabilities	$ 5,329	$ 8,099	$ 7,151

Income Taxes - Summary of Incom

Income Taxes - Summary of Income Tax Benefit (Expense) (Detail) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019
Current income tax benefit (expense):
Federal	$ 28,721	$ 8,491	$ (1,841)
State	(205)	941	(372)
Deferred income tax benefit (expense):
Federal	(343)	(8,916)	2,431
State		(1,665)	608
Income tax (expense) benefit	$ 28,583	$ (1,149)	$ 826

Income Taxes - Reconciliation o

Income Taxes - Reconciliation of Income Tax Provision at Federal Statutory Income Tax Rate and Effective Tax Rate (Detail)	12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019
Income Tax Disclosure [Abstract]
Federal statutory income tax rate	(21.00%)	(21.00%)
Federal statutory income tax rate			21.00%
State taxes, net of federal benefit	(2.30%)	(2.80%)	1.80%
Change in valuation allowance	9.90%	52.10%
Federal research and development tax credit	(5.30%)	(13.30%)	(12.80%)
Share-based compensation	2.40%	2.80%	(6.70%)
Change in deferred tax rate	(9.50%)	(10.20%)
Foreign-derived intangible income			(3.20%)
Other	(0.80%)	(4.30%)	(1.90%)
Effective income tax rate	(26.60%)	3.30%	(1.80%)

Income Taxes - Changes in the V

Income Taxes - Changes in the Valuation Allowance for Deferred Tax Assets (Detail) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Income Tax Disclosure [Abstract]
Valuation allowance, beginning of year	$ (18,259)
Increase recorded to valuation allowance	(11,039)
Initial recording of valuation allowance		$ (18,259)
Valuation allowance, end of year	$ (29,298)	$ (18,259)

Income Taxes - Net Deferred Tax

Income Taxes - Net Deferred Tax Assets and Liabilities (Detail) - USD ($) $ in Thousands	Sep. 30, 2021	Sep. 30, 2020
Deferred tax assets:
Share-based compensation	$ 11,843	$ 11,071
Tax credit carryforwards	13,170	6,574
Operating lease liability	1,232	2,468
Accrued compensation	1,284	1,598
Net operating loss carryforward	3,095	861
Accrued expenses	378	245
Other temporary differences	366	444
Total deferred tax assets	31,368	23,261
Valuation allowance, beginning of year	(29,298)	(18,259)
Net deferred tax assets	2,070	5,002
Deferred tax liabilities:
Right of use asset	(1,110)	(2,221)
Depreciation	(684)	(1,650)
Prepaid expenses	(275)	(364)
Unrealized loss	(1)	(422)
Total deferred tax liabilities	$ (2,070)	(4,657)
Net deferred income tax assets (liabilities)		$ 345

Income Taxes - Additional Infor

Income Taxes - Additional Information (Detail) $ in Thousands	12 Months Ended
	Sep. 30, 2021USD ($)	Sep. 30, 2020USD ($)
Income Tax [Line Items]
Research and development tax credit carryforward expiration year	2039
Deferred tax assets net prior to the consideration of valuation allowance	$ 29,298
Stock compensation awards	11,843
Valuation allowance	$ 29,298	$ 18,259
Description of effects of COVID-19	In response to the COVID-19 pandemic, the CARES Act was signed into law in March 2020. The CARES Act lifts certain deduction limitations originally imposed by the Tax Cuts and Jobs Act of 2017 (the “Tax Act”). Under the CARES Act, the Company is permitted to carryback net operating losses for up to five years for losses generated in fiscal 2018 through fiscal 2021. Net operating loss carrybacks were previously prohibited under the Tax Act. The CARES Act also eliminates the 80% of taxable income limitations by allowing corporate entities to fully utilize net operating loss carryforwards to offset taxable income in fiscal years 2018, 2019 or 2020. In addition, the CARES Act makes qualified improvement property eligible for 15-year cost-recovery and 100% bonus depreciation. The enactment of the CARES Act resulted in a $28,721 and $8,581 income tax benefit related to a federal net operating loss carryback at the previously enacted 35% rate in the Company’s consolidated financial statements during the years ended September 30, 2021 and 2020, respectively.
Federal income tax expense (benefit), continuing operations	$ 28,721	$ 8,581
Effective income tax rate reconciliation, tax cuts and jobs act, percent	0.35	0.35
Liability for uncertainty in income taxes, current	$ 105	$ 103
Income tax receivable	37,255	13,041
Net operating loss carryforward	$ 3,095	$ 861
Net operating loss carryforward, state, expiration year	2040
Federal [Member]
Income Tax [Line Items]
Research and development tax credit carryforward	$ 11,251
State [Member]
Income Tax [Line Items]
Research and development tax credit carryforward	2,058
Federal Research and Development [Member]
Income Tax [Line Items]
Research and development tax credit carryforward	$ 13,170

Income Taxes - Schedule of Reco

Income Taxes - Schedule of Reconciliation of Uncertain Tax Positions (Detail) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Income Tax Disclosure [Abstract]
Beginning Balance	$ 844	$ 1,650
Additions based on tax positions for the current period	10	11
Reductions for tax positions due to lapse of statute of limitations	(134)	(719)
Reductions for tax positions of prior periods	(98)	(98)
Ending Balance	$ 622	$ 844

401(k) Plan - Additional Inform

401(k) Plan - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019
Compensation Related Costs [Abstract]
Benefits charged to operating expenses	$ 1,353	$ 1,190	$ 1,068

Subsequent Events - Additional

Subsequent Events - Additional Information (Detail) - Subsequent Events [Member] - First Lease [Member] - 500 Arsenal Street, Watertown, Massachusetts [Member]	Nov. 19, 2021
Subsequent Event [Line Items]
Lease extend period	5 years
Lease expiration date	Sep. 1, 2027

Subsequent Events - Schedule of

Subsequent Events - Schedule of Subsequent Events (Detail) - USD ($) $ in Thousands	Nov. 19, 2021	Sep. 30, 2021
Subsequent Event [Line Items]
2022		$ 4,391
2023		675
2024		519
2025		0
2026		0
Total future minimum lease payments		$ 5,585
Subsequent Events [Member]
Subsequent Event [Line Items]
2022	$ 2,487
2023	3,502
2024	3,607
2025	3,715
2026	3,827
Thereafter	3,604
Total future minimum lease payments	$ 20,742