Enanta Pharmaceuticals (ENTA) 10-Q 9 Aug 21 2021 Q3 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	9 Months Ended
	Jun. 30, 2021	Jul. 29, 2021
Cover [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Jun. 30, 2021
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	Q3
Trading Symbol	ENTA
Entity Registrant Name	ENANTA PHARMACEUTICALS, INC
Entity Central Index Key	0001177648
Current Fiscal Year End Date	--09-30
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity File Number	001-35839
Security Exchange Name	NASDAQ
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
Title of 12(b) Security	Common Stock, par value $0.01 per share
Local Phone Number	607-0800
Entity Incorporation, State or Country Code	DE
Document Transition Report	false
Document Quarterly Report	true
Entity Interactive Data Current	Yes
Entity Current Reporting Status	Yes
Entity Common Stock, Shares Outstanding		20,214,850

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Jun. 30, 2021	Sep. 30, 2020
Current assets:
Cash and cash equivalents	$ 4,601	$ 87,131
Short-term marketable securities	252,223	299,518
Accounts receivable	21,624	23,492
Prepaid expenses and other current assets	12,137	13,655
Income tax receivable	30,570	13,041
Total current assets	321,155	436,837
Long-term marketable securities	115,706	32,634
Property and equipment, net	6,613	8,596
Deferred tax assets	345	345
Operating lease, right-of-use assets	5,917	7,020
Restricted cash	608	608
Other long-term assets	92	92
Total assets	450,436	486,132
Current liabilities:
Accounts payable	5,895	5,737
Accrued expenses and other current liabilities	17,695	14,159
Operating lease liabilities	5,034	4,261
Total current liabilities	28,624	24,157
Operating lease liabilities, net of current portion	1,637	3,838
Series 1 nonconvertible preferred stock	1,479	1,479
Other long-term liabilities	846	1,078
Total liabilities	32,586	30,552
Commitments and contingencies (Note 11)
Stockholders' equity:
Common stock; $0.01 par value per share, 100,000 shares authorized; 20,211 and 20,077 shares issued and outstanding at June 30, 2021 and September 30, 2020, respectively	202	201
Additional paid-in capital	344,737	326,963
Accumulated other comprehensive income (loss)	(264)	844
Retained earnings	73,175	127,572
Total stockholders' equity	417,850	455,580
Total liabilities and stockholders' equity	$ 450,436	$ 486,132

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - $ / shares	Jun. 30, 2021	Sep. 30, 2020
Statement Of Financial Position [Abstract]
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	100,000,000	100,000,000
Common stock, shares issued	20,211,000	20,077,000
Common stock, shares outstanding	20,211,000	20,077,000

Consolidated Statements of Oper

Consolidated Statements of Operations - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Income Statement [Abstract]
Royalty revenue	$ 21,624	$ 18,653	$ 73,499	$ 98,842
Type Of Revenue Extensible List	us-gaap:RoyaltyMember	us-gaap:RoyaltyMember	us-gaap:RoyaltyMember	us-gaap:RoyaltyMember
Operating expenses:
Research and development	$ 46,994	$ 34,682	$ 125,165	$ 100,070
General and administrative	8,477	6,823	24,180	20,628
Total operating expenses	55,471	41,505	149,345	120,698
Income (Loss) from operations	(33,847)	(22,852)	(75,846)	(21,856)
Other income (expense):
Other income (expense), net	439	1,445	1,661	5,471
Total other income (expense), net	439	1,445	1,661	5,471
Income (Loss) before income taxes	(33,408)	(21,407)	(74,185)	(16,385)
Income tax benefit	9,384	7,142	19,788	9,558
Net Income (loss)	$ (24,024)	$ (14,265)	$ (54,397)	$ (6,827)
Net Income (loss) per share:
Basic	$ (1.19)	$ (0.71)	$ (2.70)	$ (0.34)
Diluted	$ (1.19)	$ (0.71)	$ (2.70)	$ (0.34)
Weighted average shares outstanding:
Basic	20,201	20,020	20,155	19,897
Diluted	20,201	20,020	20,155	19,897

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Income (Loss) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Statement Of Income And Comprehensive Income [Abstract]
Net Income (loss)	$ (24,024)	$ (14,265)	$ (54,397)	$ (6,827)
Other comprehensive income (loss):
Net unrealized gains (losses) on marketable securities, net of tax of $0, $271, $0 and $418	(319)	850	(1,108)	1,312
Total other comprehensive income (loss), net of tax	(319)	850	(1,108)	1,312
Comprehensive Income (loss)	$ (24,343)	$ (13,415)	$ (55,505)	$ (5,515)

Consolidated Statements of Co_2

Consolidated Statements of Comprehensive Income (Loss) (Parenthetical) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Statement Of Income And Comprehensive Income [Abstract]
Net unrealized gains (losses) on marketable securities, tax	$ 0	$ 271	$ 0	$ 418

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, 2019	$ 462,492	$ 197	$ 298,409	$ 146	$ 163,740
Beginning Balance, Shares at Sep. 30, 2019		19,703
Exercise of stock options	2,306	$ 1	2,305
Exercise of stock options, Shares		76
Vesting of restricted stock units, net of withholding, Shares		31
Vesting of restricted stock units, net of withholding	(1,140)		(1,140)
Stock-based compensation expense	5,098		5,098
Other comprehensive income (loss), net of tax	88			88
Net Income (loss)	13,443				13,443
Ending Balance at Dec. 31, 2019	482,287	$ 198	304,672	234	177,183
Ending Balance, Shares at Dec. 31, 2019		19,810
Beginning Balance at Sep. 30, 2019	462,492	$ 197	298,409	146	163,740
Beginning Balance, Shares at Sep. 30, 2019		19,703
Other comprehensive income (loss), net of tax	1,312
Net Income (loss)	(6,827)
Ending Balance at Jun. 30, 2020	480,557	$ 201	321,985	1,458	156,913
Ending Balance, Shares at Jun. 30, 2020		20,070
Beginning Balance at Dec. 31, 2019	482,287	$ 198	304,672	234	177,183
Beginning Balance, Shares at Dec. 31, 2019		19,810
Exercise of stock options	4,716	$ 2	4,714
Exercise of stock options, Shares		160
Vesting of restricted stock units, net of withholding, Shares		16
Vesting of restricted stock units, net of withholding	(358)		(358)
Stock-based compensation expense	4,977		4,977
Other comprehensive income (loss), net of tax	374			374
Net Income (loss)	(6,005)				(6,005)
Ending Balance at Mar. 31, 2020	485,991	$ 200	314,005	608	171,178
Ending Balance, Shares at Mar. 31, 2020		19,986
Exercise of stock options	3,226	$ 1	3,225
Exercise of stock options, Shares		84
Stock-based compensation expense	4,755		4,755
Other comprehensive income (loss), net of tax	850			850
Net Income (loss)	(14,265)				(14,265)
Ending Balance at Jun. 30, 2020	480,557	$ 201	321,985	1,458	156,913
Ending Balance, Shares at Jun. 30, 2020		20,070
Beginning Balance at Sep. 30, 2020	455,580	$ 201	326,963	844	127,572
Beginning Balance, Shares at Sep. 30, 2020		20,077
Exercise of stock options	833		833
Exercise of stock options, Shares		33
Vesting of restricted stock units, net of withholding, Shares		32
Vesting of restricted stock units, net of withholding	(534)		(534)
Stock-based compensation expense	4,883		4,883
Other comprehensive income (loss), net of tax	(439)			(439)
Net Income (loss)	(8,328)				(8,328)
Ending Balance at Dec. 31, 2020	451,995	$ 201	332,145	405	119,244
Ending Balance, Shares at Dec. 31, 2020		20,142
Beginning Balance at Sep. 30, 2020	$ 455,580	$ 201	326,963	844	127,572
Beginning Balance, Shares at Sep. 30, 2020		20,077
Exercise of stock options, Shares	102
Other comprehensive income (loss), net of tax	$ (1,108)
Net Income (loss)	(54,397)
Ending Balance at Jun. 30, 2021	417,850	$ 202	344,737	(264)	73,175
Ending Balance, Shares at Jun. 30, 2021		20,211
Beginning Balance at Dec. 31, 2020	451,995	$ 201	332,145	405	119,244
Beginning Balance, Shares at Dec. 31, 2020		20,142
Exercise of stock options	1,152	$ 1	1,151
Exercise of stock options, Shares		43
Stock-based compensation expense	5,280		5,280
Other comprehensive income (loss), net of tax	(350)			(350)
Net Income (loss)	(22,045)				(22,045)
Ending Balance at Mar. 31, 2021	436,032	$ 202	338,576	55	97,199
Ending Balance, Shares at Mar. 31, 2021		20,185
Exercise of stock options	686		686
Exercise of stock options, Shares		26
Stock-based compensation expense	5,475		5,475
Other comprehensive income (loss), net of tax	(319)			(319)
Net Income (loss)	(24,024)				(24,024)
Ending Balance at Jun. 30, 2021	$ 417,850	$ 202	$ 344,737	$ (264)	$ 73,175
Ending Balance, Shares at Jun. 30, 2021		20,211

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Jun. 30, 2021	Jun. 30, 2020
Cash flows from operating activities
Net loss	$ (54,397)	$ (6,827)
Adjustments to reconcile net income to net cash provided by operating activities:
Stock-based compensation expense	15,638	14,830
Depreciation and amortization expense	2,528	2,735
Deferred income taxes		(4,366)
Premium paid on marketable securities	(3,427)	(3,094)
(Accretion) amortization of (discount) premium on marketable securities	1,516	(95)
Other non-cash items		(51)
Change in operating assets and liabilities:
Accounts receivable	1,868	32,660
Prepaid expenses and other current assets	1,518	(5,161)
Income tax receivable	(17,529)	(4,268)
Operating lease, right-of-use assets	4,019	2,182
Accounts payable	195	(672)
Accrued expenses	3,671	(1,936)
Operating lease liabilities	(4,343)	(2,446)
Other long-term liabilities	(232)	(942)
Net cash provided by (used in) operating activities	(48,975)	22,549
Cash flows from investing activities
Purchase of marketable securities	(307,949)	(267,587)
Proceeds from maturities and sale of marketable securities	272,974	286,028
Purchase of property and equipment	(717)	(1,115)
Net cash provided by (used in) investing activities	(35,692)	17,326
Cash flows from financing activities
Proceeds from exercise of stock options	2,671	10,248
Payments for settlement of share-based awards	(534)	(1,498)
Net cash provided by financing activities	2,137	8,750
Net increase (decrease) in cash, cash equivalents and restricted cash	(82,530)	48,625
Cash, cash equivalents and restricted cash at beginning of period	87,739	51,838
Cash, cash equivalents and restricted cash at end of period	5,209	100,463
Supplemental disclosure of non-cash information:
Purchases of fixed assets included in accounts payable and accrued expenses	16	299
Operating lease liabilities arising from obtaining right-of-use assets	$ 3,057	$ 2,676

Nature of the Business and Basi

Nature of the Business and Basis of Presentation	9 Months Ended
	Jun. 30, 2021
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Nature of the Business and Basis of Presentation	1. Nature of the Business and Basis of Presentation 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 ® ® 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: 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 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 SARS-CoV-2 virus. National, state and local governments in affected regions have implemented and may continue to implement varying 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 of the impact on the Company’s business and clinical trials to date has largely been delays in the conduct of out-sourced preclinical testing and ongoing and future clinical trials, as well as reductions in the number of patients accessing AbbVie’s HCV regimens. The full extent to which the COVID-19 pandemic will continue to 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 its variants, public health actions taken to contain the pandemic and mitigate its economic effects and to roll out vaccinations worldwide, as well as the cumulative economic impact of all of these factors . Unaudited Interim Financial Information The consolidated balance sheet at September 30, 2020 was derived from audited financial statements but does not include all disclosures required by accounting principles generally accepted in the United States of America (“GAAP”). The accompanying unaudited consolidated financial statements as of June 30, 2021 and for the three and nine months ended June 30, 2021 and 2020 have been prepared by the Company pursuant to the rules and regulations of the Securities and Exchange Commission (“SEC”) for interim financial statements. Certain information and footnote disclosures normally included in financial statements prepared in accordance with GAAP have been condensed or omitted pursuant to such rules and regulations. These financial statements should be read in conjunction with the Company’s audited financial statements and the notes thereto included in the Company’s Annual Report on Form 10-K for the year ended September 30, 2020. In the opinion of management, all adjustments, consisting of normal recurring adjustments necessary for a fair statement of the Company’s financial position as of June 30, 2021 and results of operations for the three and nine months ended June 30, 2021 and 2020 and cash flows for the nine months ended June 30, 2021 and 2020, have been made. The results of operations for the three and nine months ended June 30, 2021 are not necessarily indicative of the results of operations that may be expected for subsequent quarters or the year ending September 30, 2021. The accompanying consolidated financial statements have been prepared in conformity with GAAP. All amounts in the consolidated financial statements and in the notes to the consolidated financial statements, except per share amounts, are in thousands unless otherwise indicated.

Summary of Significant Accounti

Summary of Significant Accounting Policies	9 Months Ended
	Jun. 30, 2021
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	2. Summary of Significant Accounting Policies For the Company’s Significant Accounting Policies, please refer to its Annual Report on Form 10-K for the fiscal year ended September 30, 2020. Any reference in these notes to applicable guidance is meant to refer to the authoritative GAAP as found in the Accounting Standards Codification (“ASC”) and Accounting Standards Update (“ASU”) of the Financial Accounting Standards Board (“FASB”). 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 Series 1 nonconvertible preferred stock and stock-based awards; the accrual of research and development expenses, and the accounting for income taxes, including uncertain tax positions and the valuation of net deferred tax assets. quarantines, border closures, increased border controls, travel restrictions, shelter-in-place orders and shutdowns, business closures, cancellations of public gatherings and other measures. June 30, 2021 Recently Adopted 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. The adoption of ASU 2016-13 did not have a material impact on the consolidated financial statements. Recently Issued Accounting Pronouncements In December 2019, the FASB issued ASU 2019-12, Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes (“ASU 2019-12”). This standard simplifies various aspects of the income tax accounting guidance in ASC 740, including requirements related to hybrid tax regimes, the tax basis step-up in goodwill obtained in a transaction that is not a business combination, separate financial statements of entities not subject to tax, the intra-period tax allocation exception to the incremental approach, ownership changes in investments, changes from a subsidiary to an equity method investment, interim-period accounting for enacted changes in tax law, and the year-to-date loss limitation in interim-period tax accounting. This amendment is effective for the Company in the fiscal year beginning October 1, 2021; however, early adoption is permitted. The Company is currently in the process of evaluating the impact that ASU 2019-12 may have on its consolidated financial statements. Other accounting standards that have been issued or proposed by the FASB or other standards-setting bodies that do not require adoption until a future date are not expected to have a material impact on the Company’s consolidated financial statements upon adoption.

Fair Value of Financial Assets

Fair Value of Financial Assets and Liabilities	9 Months Ended
	Jun. 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 June 30, 2021 and September 30, 2020, and indicate the fair value hierarchy of the valuation inputs utilized to determine such fair value: Fair Value Measurements at June 30, 2021 Using: Level 1 Level 2 Level 3 Total (in thousands) Assets: Cash equivalents: Money market funds $ 1,687 $ — $ — $ 1,687 Marketable securities: U.S. Treasury notes 101,221 — — 101,221 Corporate bonds — 153,191 — 153,191 Commercial paper — 113,517 — 113,517 $ 102,908 $ 266,708 $ — $ 369,616 Liabilities: Series 1 nonconvertible preferred stock $ — $ — $ 1,479 $ 1,479 $ — $ — $ 1,479 $ 1,479 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 Corporate bonds — 144,035 — 144,035 Commercial paper — 93,909 — 93,909 $ 175,710 $ 237,944 $ — $ 413,654 Liabilities: Series 1 nonconvertible preferred stock $ — $ — $ 1,479 1,479 $ — $ — $ 1,479 $ 1,479 During the nine months ended June 30, 2021 and 2020, there were no transfers between Level 1, Level 2 and Level 3. The outstanding shares of Series 1 nonconvertible preferred stock are measured at fair value. The fair value of these instruments was 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 exercise. Changes in the fair value 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 outstanding Series 1 nonconvertible preferred stock using probability-weighted discounted cash flow include the following significant unobservable inputs: Range June 30, September 30, Unobservable Input 2021 2020 Probabilities of payout 0%-60% 0%-60% Discount rate 4.25% 4.25% The following table provides a rollforward of the aggregate fair values of the Company’s outstanding Series 1 nonconvertible preferred stock for which fair value is determined by Level 3 inputs: Series 1 Nonconvertible Preferred Stock Balance, September 30, 2020 $ 1,479 Change in fair value of nonconvertible preferred stock — Balance, June 30, 2021 $ 1,479

Marketable Securities

Marketable Securities	9 Months Ended
	Jun. 30, 2021
Investments Debt And Equity Securities [Abstract]
Marketable Securities	4. Marketable Securities As of June 30, 2021 and September 30, 2020, the fair value of available-for-sale marketable securities, by type of security, was as follows: June 30, 2021 Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Credit Losses Fair Value (in thousands) Corporate bonds $ 153,080 $ 211 $ (100 ) $ — $ 153,191 Commercial paper 113,517 — — — 113,517 U.S. Treasury notes 101,211 62 (52 ) — 101,221 $ 367,808 $ 273 $ (152 ) $ — $ 367,929 September 30, 2020 Amortized Cost Gross Unrealized Gains Gross Unrealized Losses 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 June 30, 2021 and September 30, 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 $115,706 and $32,634, respectively.

Accrued Expenses and Other Long

Accrued Expenses and Other Long-Term Liabilities	9 Months Ended
	Jun. 30, 2021
Payables And Accruals [Abstract]
Accrued Expenses and Other Long-Term Liabilities	5. Accrued Expenses and Other Long-Term Liabilities Accrued expenses and other current liabilities, as well as other long-term liabilities, consisted of the following as of June 30, 2021 and September 30, 2020: June 30, September 2021 2020 (in thousands) Accrued expenses: Accrued research and development expenses $ 7,277 $ 5,407 Accrued pharmaceutical drug manufacturing 4,303 2,885 Accrued payroll and related expenses 4,363 4,777 Accrued professional fees 697 478 Accrued other 1,055 612 $ 17,695 $ 14,159 Other long-term liabilities: Uncertain tax positions $ 529 $ 788 Asset retirement obligation 317 290 $ 846 $ 1,078

AbbVie Collaboration

AbbVie Collaboration	9 Months Ended
	Jun. 30, 2021
Organization Consolidation And Presentation Of Financial Statements [Abstract]
AbbVie Collaboration	6. AbbVie Collaboration The Company has a Collaborative Development and License Agreement (as amended, the “AbbVie Agreement”), with AbbVie to identify, develop and commercialize HCV NS3 and NS3/4A protease inhibitor compounds, including paritaprevir and glecaprevir, under which the Company has received license payments, proceeds from a sale of preferred stock, research funding payments, milestone payments and royalties totaling approximately $1,096,000 through June 30, 2021. Since the Company satisfied all of its performance obligations under the AbbVie Agreement by the end of fiscal 2011, all milestone payments received since then have been recognized as revenue when the milestones were achieved by AbbVie. The Company is receiving annually tiered royalties per Company protease product ranging from ten percent up to twenty percent, or on a blended basis from ten percent 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 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.

Series 1 Nonconvertible Preferr

Series 1 Nonconvertible Preferred Stock	9 Months Ended
	Jun. 30, 2021
Debt Disclosure [Abstract]
Series 1 Nonconvertible Preferred Stock	7. Series 1 Nonconvertible Preferred Stock As of June 30, 2021, 1,930 shares of Series 1 nonconvertible preferred stock were issued and outstanding. Since these shares qualify as a derivative, the outstanding shares are carried at fair value as a liability on the Company’s consolidated balance sheet.

Stock-Based Awards

Stock-Based Awards	9 Months Ended
	Jun. 30, 2021
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Stock-Based Awards	8. Stock-Based Awards The Company grants stock-based awards, including stock options, restricted stock units and other unit awards under its 2019 Equity Incentive Plan (the “2019 Plan”), which was approved by its stockholders on February 28, 2019 and amended in March 2021. The Company also has outstanding stock option awards under its 2012 Equity Incentive Plan (the “2012 Plan”) and its amended and restated 1995 Equity Incentive Plan (the “1995 Plan”), but is no longer granting awards under these plans. The following table summarizes stock option activity, including performance-based options, for the year-to-date period ending June 30, 2021: Shares Issuable Under Options Weighted Average Exercise Price Weighted Average Remaining Contractual Term Aggregate Intrinsic Value (in thousands) (in years) (in thousands) Outstanding as of September 30, 2020 3,262 $ 49.82 6.5 $ 21,860 Granted 855 44.95 Exercised (102 ) 26.08 Forfeited (139 ) 67.27 Outstanding as of June 30, 2021 3,876 $ 48.75 6.6 $ 17,654 Options vested and expected to vest as of June 30, 2021 3,876 $ 48.75 6.6 $ 17,654 Options exercisable as of June 30, 2021 2,418 $ 45.26 5.3 $ 17,312 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 number of units granted 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. The number of shares cancelled represents the target number of shares, less any shares that vested. PSUs rTSRUs Shares Weighted Average Grant Date Fair Value Shares Weighted Average Grant Date Fair Value (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 June 30, 2021 111 $ 49.31 111 $ 31.26 Restricted Stock Units During the three months ended December 31, 2016, the Company awarded restricted stock units to its employees, which vested 50% in December 2019 and 50% in December 2020, provided the employee remained employed with the Company at the time of vesting. The fair value per share of these awards was determined based on the intrinsic value of the stock on the date of grant and is being recognized as stock-based compensation expense over the requisite service period. In November 2020, the Company awarded additional restricted stock units to its employees, which vest in equal annual installments over four years, so long as the employee remains employed with the Company at the time of vesting. The fair value per share of these awards was determined based on the intrinsic value of the stock on the date of grant and is being 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 June 30, 2021: Restricted Stock Units Weighted Average Grant Date Fair Value (in thousands, except per share data) Unvested at September 30, 2020 45 $ 30.00 Granted 123 43.57 Vested (45 ) 30.00 Cancelled (3 ) 41.15 Unvested at June 30, 2021 120 $ 43.57 Stock-Based Compensation Expense During the three and nine months ended June 30, 2021 and 2020, the Company recognized the following stock-based compensation expense: Three Months ended Nine Months Ended June 30, June 30, 2021 2020 2021 2020 (in thousands) Research and development $ 2,569 $ 2,499 $ 7,525 $ 7,678 General and administrative 2,906 2,256 8,113 7,152 $ 5,475 $ 4,755 $ 15,638 $ 14,830 Three Months ended Nine Months Ended June 30, June 30, 2021 2020 2021 2020 (in thousands) Stock options $ 4,555 $ 4,339 $ 13,418 $ 13,114 rTSRUs 405 246 1,126 968 Performance stock units 198 — 198 259 Restricted stock units 317 170 896 489 $ 5,475 $ 4,755 $ 15,638 $ 14,830 During the three months ended December 31, 2019 and three months ended June 30, 2021, the Company recognized stock-based compensation expense for performance-based stock units for which vesting became probable upon achievement of performance-based targets that occurred during the performance period. As of June 30, 2021, the Company had an aggregate of $49,337 of unrecognized stock-based compensation cost, which is expected to be recognized over a weighted average period of 2.3 years.

Net Loss Per Share

Net Loss Per Share	9 Months Ended
	Jun. 30, 2021
Earnings Per Share [Abstract]
Net Loss Per Share	9. Net Loss Per Share Basic and diluted net loss per share attributable to common stockholders was calculated as follows for the three and nine months ended June 30, 2021 and 2020: Three Months Ended Nine Months Ended June 30, June 30, 2021 2020 2021 2020 (in thousands, except per share data) Basic net loss per share: Numerator: Net loss $ (24,024 ) $ (14,265 ) $ (54,397 ) $ (6,827 ) Denominator: Weighted average common shares outstanding —basic 20,201 20,020 20,155 19,897 Net loss per share common share—basic $ (1.19 ) $ (0.71 ) $ (2.70 ) $ (0.34 ) Diluted net loss per share: Numerator: Net loss $ (24,024 ) $ (14,265 ) $ (54,397 ) $ (6,827 ) Denominator: Weighted average common shares outstanding —basic 20,201 20,020 20,155 19,897 Dilutive effect of common stock equivalents — — — — Weighted average common shares outstanding —diluted 20,201 20,020 20,155 19,897 Net loss per share common share—diluted $ (1.19 ) $ (0.71 ) $ (2.70 ) $ (0.34 ) Anti-dilutive common stock equivalents excluded from above 4,322 3,640 6,468 3,423 The impact of certain common stock equivalents was excluded from the computation of diluted net loss per share for the periods in which the Company incurred a net loss since the impact of such common stock equivalents would have been anti-dilutive.

Income Taxes

Income Taxes	9 Months Ended
	Jun. 30, 2021
Income Tax Disclosure [Abstract]
Income Taxes	10. Income Taxes For the three months ended June 30, 2021 and 2020, the Company recorded income tax benefits of $9,384 and $7,142, respectively, both of which were attributable to the Company’s domestic operations. The Company recorded an income tax benefit during the three and nine months ended June 30, 2021 due to the Company’s ability and intent to carryback its current year tax loss under the CARES Act”), which . As of June 30, 2021 the Company recorded an income tax receivable of $30,570 consisting of refunds due with respect to prior year tax payments as well as an estimated federal net operating loss carryback for fiscal 2021 for which the Company will request a refund in the future. For the three and nine months ended June 30, 2020, the Company determined the use of the discrete method was more appropriate than the annual effective tax rate method due to the sensitivity of the Company’s tax rate in that period to small changes in projected pre-tax earnings, which resulted in significant variations in the customary relationship between income tax expense and pretax income. 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 are still open under the statute for the year ended September 30, 2018 to the present. Earlier years may be examined to the extent that tax credit or net operating loss carryforwards are used in future or prior periods. The Company is not currently under examination by any jurisdiction for any tax year open under the statute. The Company had unrecognized tax benefits totaling $529 and $788 as of and , respectively. Unrecognized tax benefits 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 its income tax provision. The CARES Act lifts certain deduction limitations originally imposed by the Tax Cuts and Jobs Act of 2017 (the “2017 Tax Act”). Under the CARES Act, the Company is permitted to carry back net operating losses originating beginning in fiscal 2018 through fiscal 2021 for up to five years. Net operating loss carrybacks were previously prohibited under the 2017 Tax Act. The CARES Act also eliminates the 80% of taxable income limitations by allowing corporate entities to fully utilize net operating losses to offset taxable income in those prior years. In addition, the CARES Act makes qualified improvement property eligible for 15-year cost-recovery and 100% bonus depreciation. The impact of the CARES Act has been incorporated into the consolidated financial statements during the nine months ended June 30, 2021 and 2020 . As of June 30, 2021, the Company recorded a valuation allowance against substantially all The Company continues to believe 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’s expenses are increasing as it continues to progress its wholly-owned research and development programs, while its royalty revenues from its Collaboration Agreement with AbbVie are not increasing.

Commitments and Contingencies

Commitments and Contingencies	9 Months Ended
	Jun. 30, 2021
Commitments And Contingencies Disclosure [Abstract]
Commitments and Contingencies	1 1 . 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 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 it has not accrued any liabilities related to such obligations in its financial statements as of June 30, 2021 .

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	9 Months Ended
	Jun. 30, 2021
Accounting Policies [Abstract]
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 Series 1 nonconvertible preferred stock and stock-based awards; the accrual of research and development expenses, and the accounting for income taxes, including uncertain tax positions and the valuation of net deferred tax assets. quarantines, border closures, increased border controls, travel restrictions, shelter-in-place orders and shutdowns, business closures, cancellations of public gatherings and other measures. June 30, 2021
Recently Adopted and Issued Accounting Pronouncements	Recently Adopted 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. The adoption of ASU 2016-13 did not have a material impact on the consolidated financial statements. Recently Issued Accounting Pronouncements In December 2019, the FASB issued ASU 2019-12, Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes (“ASU 2019-12”). This standard simplifies various aspects of the income tax accounting guidance in ASC 740, including requirements related to hybrid tax regimes, the tax basis step-up in goodwill obtained in a transaction that is not a business combination, separate financial statements of entities not subject to tax, the intra-period tax allocation exception to the incremental approach, ownership changes in investments, changes from a subsidiary to an equity method investment, interim-period accounting for enacted changes in tax law, and the year-to-date loss limitation in interim-period tax accounting. This amendment is effective for the Company in the fiscal year beginning October 1, 2021; however, early adoption is permitted. The Company is currently in the process of evaluating the impact that ASU 2019-12 may have on its consolidated financial statements.

Fair Value of Financial Asset_2

Fair Value of Financial Assets and Liabilities (Tables)	9 Months Ended
	Jun. 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 June 30, 2021 and September 30, 2020, and indicate the fair value hierarchy of the valuation inputs utilized to determine such fair value: Fair Value Measurements at June 30, 2021 Using: Level 1 Level 2 Level 3 Total (in thousands) Assets: Cash equivalents: Money market funds $ 1,687 $ — $ — $ 1,687 Marketable securities: U.S. Treasury notes 101,221 — — 101,221 Corporate bonds — 153,191 — 153,191 Commercial paper — 113,517 — 113,517 $ 102,908 $ 266,708 $ — $ 369,616 Liabilities: Series 1 nonconvertible preferred stock $ — $ — $ 1,479 $ 1,479 $ — $ — $ 1,479 $ 1,479 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 Corporate bonds — 144,035 — 144,035 Commercial paper — 93,909 — 93,909 $ 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 Outstanding Series 1 Nonconvertible Preferred Stock	The recurring Level 3 fair value measurements of the Company’s outstanding Series 1 nonconvertible preferred stock using probability-weighted discounted cash flow include the following significant unobservable inputs: Range June 30, September 30, Unobservable Input 2021 2020 Probabilities of payout 0%-60% 0%-60% Discount rate 4.25% 4.25%
Rollforward of Aggregate Fair Values of Outstanding Series 1 Nonconvertible Preferred Stock	The following table provides a rollforward of the aggregate fair values of the Company’s outstanding Series 1 nonconvertible preferred stock for which fair value is determined by Level 3 inputs: Series 1 Nonconvertible Preferred Stock Balance, September 30, 2020 $ 1,479 Change in fair value of nonconvertible preferred stock — Balance, June 30, 2021 $ 1,479

Marketable Securities (Tables)

Marketable Securities (Tables)	9 Months Ended
	Jun. 30, 2021
Investments Debt And Equity Securities [Abstract]
Fair Value of Available-for-Sale Marketable Securities by Type of Security	As of June 30, 2021 and September 30, 2020, the fair value of available-for-sale marketable securities, by type of security, was as follows: June 30, 2021 Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Credit Losses Fair Value (in thousands) Corporate bonds $ 153,080 $ 211 $ (100 ) $ — $ 153,191 Commercial paper 113,517 — — — 113,517 U.S. Treasury notes 101,211 62 (52 ) — 101,221 $ 367,808 $ 273 $ (152 ) $ — $ 367,929 September 30, 2020 Amortized Cost Gross Unrealized Gains Gross Unrealized Losses 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

Accrued Expenses and Other Lo_2

Accrued Expenses and Other Long-Term Liabilities (Tables)	9 Months Ended
	Jun. 30, 2021
Payables And Accruals [Abstract]
Accrued Expenses and Other Current Liabilities as well as Other Long-Term Liabilities	Accrued expenses and other current liabilities, as well as other long-term liabilities, consisted of the following as of June 30, 2021 and September 30, 2020: June 30, September 2021 2020 (in thousands) Accrued expenses: Accrued research and development expenses $ 7,277 $ 5,407 Accrued pharmaceutical drug manufacturing 4,303 2,885 Accrued payroll and related expenses 4,363 4,777 Accrued professional fees 697 478 Accrued other 1,055 612 $ 17,695 $ 14,159 Other long-term liabilities: Uncertain tax positions $ 529 $ 788 Asset retirement obligation 317 290 $ 846 $ 1,078

Stock-Based Awards (Tables)

Stock-Based Awards (Tables)	9 Months Ended
	Jun. 30, 2021
Summary of Stock Option Activity Including Performance Based Options	The following table summarizes stock option activity, including performance-based options, for the year-to-date period ending June 30, 2021: Shares Issuable Under Options Weighted Average Exercise Price Weighted Average Remaining Contractual Term Aggregate Intrinsic Value (in thousands) (in years) (in thousands) Outstanding as of September 30, 2020 3,262 $ 49.82 6.5 $ 21,860 Granted 855 44.95 Exercised (102 ) 26.08 Forfeited (139 ) 67.27 Outstanding as of June 30, 2021 3,876 $ 48.75 6.6 $ 17,654 Options vested and expected to vest as of June 30, 2021 3,876 $ 48.75 6.6 $ 17,654 Options exercisable as of June 30, 2021 2,418 $ 45.26 5.3 $ 17,312
Summary of Restricted Stock Unit Activity	The following table summarizes the restricted stock unit activity for the year-to-date period ending June 30, 2021: Restricted Stock Units Weighted Average Grant Date Fair Value (in thousands, except per share data) Unvested at September 30, 2020 45 $ 30.00 Granted 123 43.57 Vested (45 ) 30.00 Cancelled (3 ) 41.15 Unvested at June 30, 2021 120 $ 43.57
Stock-Based Compensation Expense	During the three and nine months ended June 30, 2021 and 2020, the Company recognized the following stock-based compensation expense: Three Months ended Nine Months Ended June 30, June 30, 2021 2020 2021 2020 (in thousands) Research and development $ 2,569 $ 2,499 $ 7,525 $ 7,678 General and administrative 2,906 2,256 8,113 7,152 $ 5,475 $ 4,755 $ 15,638 $ 14,830 Three Months ended Nine Months Ended June 30, June 30, 2021 2020 2021 2020 (in thousands) Stock options $ 4,555 $ 4,339 $ 13,418 $ 13,114 rTSRUs 405 246 1,126 968 Performance stock units 198 — 198 259 Restricted stock units 317 170 896 489 $ 5,475 $ 4,755 $ 15,638 $ 14,830
Performance Share Units and Relative Total Stockholder Return Units [Member]
Summary of PSUs and rTSRUs Activity	The following table summarizes PSU and rTSRU activity for the year-to-date period ending March 31, 2021: PSUs rTSRUs Shares Weighted Average Grant Date Fair Value Shares Weighted Average Grant Date Fair Value (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 June 30, 2021 111 $ 49.31 111 $ 31.26

Net Loss Per Share (Tables)

Net Loss Per Share (Tables)	9 Months Ended
	Jun. 30, 2021
Earnings Per Share [Abstract]
Basic and Diluted Net Loss Per Share Attributable to Common Stockholders	Basic and diluted net loss per share attributable to common stockholders was calculated as follows for the three and nine months ended June 30, 2021 and 2020: Three Months Ended Nine Months Ended June 30, June 30, 2021 2020 2021 2020 (in thousands, except per share data) Basic net loss per share: Numerator: Net loss $ (24,024 ) $ (14,265 ) $ (54,397 ) $ (6,827 ) Denominator: Weighted average common shares outstanding —basic 20,201 20,020 20,155 19,897 Net loss per share common share—basic $ (1.19 ) $ (0.71 ) $ (2.70 ) $ (0.34 ) Diluted net loss per share: Numerator: Net loss $ (24,024 ) $ (14,265 ) $ (54,397 ) $ (6,827 ) Denominator: Weighted average common shares outstanding —basic 20,201 20,020 20,155 19,897 Dilutive effect of common stock equivalents — — — — Weighted average common shares outstanding —diluted 20,201 20,020 20,155 19,897 Net loss per share common share—diluted $ (1.19 ) $ (0.71 ) $ (2.70 ) $ (0.34 ) Anti-dilutive common stock equivalents excluded from above 4,322 3,640 6,468 3,423

Nature of the Business and Ba_2

Nature of the Business and Basis of Presentation - Additional Information (Detail)	9 Months Ended
	Jun. 30, 2021
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Entity incorporated, in year	1995

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	Jun. 30, 2021	Sep. 30, 2020
Assets:
Marketable securities	$ 367,929	$ 332,152
Assets, Fair Value Disclosure, Total	369,616	413,654
Liabilities:
Liabilities, Fair Value Disclosure, Total	1,479	1,479
Series 1 Nonconvertible Preferred Stock [Member]
Liabilities:
Liabilities	1,479	1,479
Level 1 [Member]
Assets:
Assets, Fair Value Disclosure, Total	102,908	175,710
Level 2 [Member]
Assets:
Assets, Fair Value Disclosure, Total	266,708	237,944
Level 3 [Member]
Liabilities:
Liabilities, Fair Value Disclosure, Total	1,479	1,479
Level 3 [Member] | Series 1 Nonconvertible Preferred Stock [Member]
Liabilities:
Liabilities	1,479	1,479
Money Market Funds [Member]
Assets:
Cash equivalents	1,687	81,502
Money Market Funds [Member] | Level 1 [Member]
Assets:
Cash equivalents	1,687	81,502
Corporate Bonds [Member]
Assets:
Marketable securities	153,191	144,035
Corporate Bonds [Member] | Level 2 [Member]
Assets:
Marketable securities	153,191	144,035
Commercial Paper [Member]
Assets:
Marketable securities	113,517	93,909
Commercial Paper [Member] | Level 2 [Member]
Assets:
Marketable securities	113,517	93,909
U.S. Treasury Notes [Member]
Assets:
Marketable securities	101,221	94,208
U.S. Treasury Notes [Member] | Level 1 [Member]
Assets:
Marketable securities	$ 101,221	$ 94,208

Fair Value of Financial Asset_4

Fair Value of Financial Assets and Liabilities - Additional Information (Detail) - USD ($)	9 Months Ended
	Jun. 30, 2021	Jun. 30, 2020
Fair Value Disclosures [Abstract]
Transfers between Level 1, Level 2 and Level 3	$ 0	$ 0

Fair Value of Financial Asset_5

Fair Value of Financial Assets and Liabilities - Fair Value Measurements of the Company's Outstanding Series 1 Nonconvertible Preferred Stock (Detail) - Level 3 [Member]	Jun. 30, 2021	Sep. 30, 2020
Discount Rate [Member]
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Range	4.25	4.25
Minimum [Member] | Probabilities of Payout [Member]
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Range	0	0
Maximum [Member] | Probabilities of Payout [Member]
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Range	60	60

Fair Value of Financial Asset_6

Fair Value of Financial Assets and Liabilities - Rollforward of Aggregate Fair Values of Outstanding Series 1 Nonconvertible Preferred Stock (Detail) - Series 1 Nonconvertible Preferred Stock [Member] $ in Thousands	Jun. 30, 2021USD ($)
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning Balance	$ 1,479
Ending Balance	$ 1,479

Marketable Securities - Fair Va

Marketable Securities - Fair Value of Available-for-Sale Marketable Securities by Type of Security (Detail) - USD ($) $ in Thousands	Jun. 30, 2021	Sep. 30, 2020
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 367,808	$ 330,923
Gross Unrealized Gains	273	1,243
Gross Unrealized Losses	(152)	(14)
Fair Value	367,929	332,152
Commercial Paper [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	113,517	93,909
Fair Value	113,517	93,909
Corporate Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	153,080	143,274
Gross Unrealized Gains	211	775
Gross Unrealized Losses	(100)	(14)
Fair Value	153,191	144,035
U.S. Treasury Notes [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	101,211	93,740
Gross Unrealized Gains	62	468
Gross Unrealized Losses	(52)
Fair Value	$ 101,221	$ 94,208

Marketable Securities - Additio

Marketable Securities - Additional Information (Detail) - USD ($) $ in Thousands	9 Months Ended
	Jun. 30, 2021	Sep. 30, 2020
Schedule of Available-for-sale Securities [Line Items]
Long-term marketable securities	$ 115,706	$ 32,634
Maximum [Member] | Short Term Marketable Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Maturity period of the marketable securities	1 year
Long Term Marketable Securities [Member] | Maximum [Member] | Corporate Bonds and U.S. Treasury Notes [Member]
Schedule of Available-for-sale Securities [Line Items]
Maturity period of the marketable securities	3 years
Long Term Marketable Securities [Member] | Minimum [Member] | Corporate Bonds and U.S. Treasury Notes [Member]
Schedule of Available-for-sale Securities [Line Items]
Maturity period of the marketable securities	1 year

Accrued Expenses and Other Lo_3

Accrued Expenses and Other Long-Term Liabilities - Accrued Expenses and Other Current Liabilities as well as Other Long-Term Liabilities (Detail) - USD ($) $ in Thousands	Jun. 30, 2021	Sep. 30, 2020
Accrued expenses:
Accrued research and development expenses	$ 7,277	$ 5,407
Accrued pharmaceutical drug manufacturing	4,303	2,885
Accrued payroll and related expenses	4,363	4,777
Accrued professional fees	697	478
Accrued other	1,055	612
Accrued expenses	17,695	14,159
Other long-term liabilities:
Uncertain tax positions	529	788
Asset retirement obligation	317	290
Other long-term liabilities	$ 846	$ 1,078

AbbVie Collaboration - Addition

AbbVie Collaboration - Additional Information (Detail) - AbbVie [Member] $ in Thousands	9 Months Ended
	Jun. 30, 2021USD ($)
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Cash consideration received under collaboration from sale of preferred stock, research funding payments, milestone payments and royalties	$ 1,096,000
Collaboration agreement tiered royalty description	from ten percent up to twenty percent, or on a blended basis from ten percent up to the high teens, on the portion of AbbVie’s calendar year net sales

Series 1 Nonconvertible Prefe_2

Series 1 Nonconvertible Preferred Stock - Additional Information (Detail) - Series 1 Nonconvertible Preferred Stock [Member] shares in Thousands	Jun. 30, 2021shares
Class Of Stock [Line Items]
Preferred stock, shares issued	1,930
Preferred stock, shares outstanding	1,930

Stock-Based Awards - Summary of

Stock-Based Awards - Summary of Stock Option Activity Including Performance Based Options (Detail) $ / shares in Units, shares in Thousands, $ in Thousands	9 Months Ended	12 Months Ended
	Jun. 30, 2021USD ($)$ / sharesshares	Sep. 30, 2020USD ($)$ / sharesshares
Options
Outstanding as of beginning of period | shares	3,262
Granted | shares	855
Exercised | shares	(102)
Forfeited | shares	(139)
Outstanding as of end of period | shares	3,876	3,262
Options vested and expected to vest as of end of period | shares	3,876
Options exercisable as of end of period | shares	2,418
Weighted Average Exercise Price
Outstanding | $ / shares	$ 49.82
Granted | $ / shares	44.95
Exercised | $ / shares	26.08
Forfeited | $ / shares	67.27
Outstanding | $ / shares	48.75	$ 49.82
Options vested and expected to vest as of end of period | $ / shares	48.75
Options exercisable as of end of period | $ / shares	$ 45.26
Weighted Average Remaining Contractual Term
Outstanding as of end of period	6 years 7 months 6 days	6 years 6 months
Options vested and expected to vest as of end period	6 years 7 months 6 days
Options exercisable as of end of period	5 years 3 months 19 days
Aggregate Intrinsic Value
Aggregate Intrinsic Value | $	$ 17,654	$ 21,860
Options vested and expected to vest as of June 30, 2021 | $	17,654
Options exercisable as of end of period | $	$ 17,312

Stock-Based Awards - Additional

Stock-Based Awards - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Dec. 31, 2020	Dec. 31, 2016	Jun. 30, 2021
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period	4 years
Aggregate of unrecognized stock-based compensation cost			$ 49,337
Weighted average recognition period			2 years 3 months 18 days
Restricted Stock Units [Member] | Tranche One [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting percentage		50.00%
Vested period		2019-12
Restricted Stock Units [Member] | Tranche Two [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting percentage		50.00%
Vested period		2020-12
Executive Officers [Member] | Relative Total Stockholder Return Units [Member] | Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares range percentage			0.00%
Executive Officers [Member] | Relative Total Stockholder Return Units [Member] | Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares range percentage			150.00%

Stock-Based Awards - Summary _2

Stock-Based Awards - Summary of PSUs and rTSRUs Activity (Detail) shares in Thousands	9 Months Ended
	Jun. 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, Unvested beginning balance | $ / shares	$ 65.23
Weighted Average Grant Date Fair Value, Granted | $ / shares	44.58
Weighted Average Grant Date Fair Value, Cancelled | $ / shares	67.13
Weighted Average Grant Date Fair Value, 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, Unvested beginning balance | $ / shares	$ 46.46
Weighted Average Grant Date Fair Value, Granted | $ / shares	26.55
Weighted Average Grant Date Fair Value, Cancelled | $ / shares	47.42
Weighted Average Grant Date Fair Value, Unvested ending balance | $ / shares	$ 31.26

Stock-Based Awards - Summary _3

Stock-Based Awards - Summary of Restricted Stock Unit Activity (Detail) - Restricted Stock Units [Member] shares in Thousands	9 Months Ended
	Jun. 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	(3)
Unvested, ending balance | shares	120
Weighted Average Grant Date Fair Value, Unvested beginning balance | $ / shares	$ 30
Weighted Average Grant Date Fair Value, Granted | $ / shares	43.57
Weighted Average Grant Date Fair Value, Vested | $ / shares	30
Weighted Average Grant Date Fair Value, Cancelled | $ / shares	41.15
Weighted Average Grant Date Fair Value, Unvested ending balance | $ / shares	$ 43.57

Stock-Based Awards - Stock-Base

Stock-Based Awards - Stock-Based Compensation Expense (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	$ 5,475	$ 4,755	$ 15,638	$ 14,830
Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	4,555	4,339	13,418	13,114
Performance Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	198		198	259
rTSRUs [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	405	246	1,126	968
Restricted Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	317	170	896	489
Research and Development [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	2,569	2,499	7,525	7,678
General and Administrative [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	$ 2,906	$ 2,256	$ 8,113	$ 7,152

Net Income (Loss) Per Share - B

Net Income (Loss) Per Share - Basic and Diluted Net Income (Loss) Per Share Attributable to Common Stockholders (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended						9 Months Ended
	Jun. 30, 2021	Mar. 31, 2021	Dec. 31, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Jun. 30, 2021	Jun. 30, 2020
Basic net loss per share:
Net loss	$ (24,024)	$ (22,045)	$ (8,328)	$ (14,265)	$ (6,005)	$ 13,443	$ (54,397)	$ (6,827)
Weighted average common shares outstanding —basic	20,201			20,020			20,155	19,897
Net loss per share common share—basic	$ (1.19)			$ (0.71)			$ (2.70)	$ (0.34)
Diluted net loss per share:
Net loss	$ (24,024)	$ (22,045)	$ (8,328)	$ (14,265)	$ (6,005)	$ 13,443	$ (54,397)	$ (6,827)
Basic	20,201			20,020			20,155	19,897
Weighted average common shares outstanding —diluted	20,201			20,020			20,155	19,897
Net loss per share common share—diluted	$ (1.19)			$ (0.71)			$ (2.70)	$ (0.34)
Anti-dilutive common stock equivalents excluded from above	4,322			3,640			6,468	3,423

Income Taxes - Additional Infor

Income Taxes - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Sep. 30, 2020
Income Tax Disclosure [Abstract]
Income tax benefit	$ 9,384	$ 7,142	$ 19,788	$ 9,558
Income tax receivable	30,570		30,570		$ 13,041
Unrecognized tax benefits	$ 529		$ 529		$ 788
Description of effects of COVID-19			The CARES Act lifts certain deduction limitations originally imposed by the Tax Cuts and Jobs Act of 2017 (the “2017 Tax Act”). Under the CARES Act, the Company is permitted to carry back net operating losses originating beginning in fiscal 2018 through fiscal 2021 for up to five years. Net operating loss carrybacks were previously prohibited under the 2017 Tax Act. The CARES Act also eliminates the 80% of taxable income limitations by allowing corporate entities to fully utilize net operating losses to offset taxable income in those prior years. In addition, the CARES Act makes qualified improvement property eligible for 15-year cost-recovery and 100% bonus depreciation.