Enanta Pharmaceuticals (ENTA) 10-Q 10 May 21 2021 Q2 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	6 Months Ended
	Mar. 31, 2021	Apr. 26, 2021
Cover [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Mar. 31, 2021
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	Q2
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		20,195,129

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Mar. 31, 2021	Sep. 30, 2020
Current assets:
Cash and cash equivalents	$ 77,126	$ 87,131
Short-term marketable securities	298,821	299,518
Accounts receivable	20,132	23,492
Prepaid expenses and other current assets	32,140	26,696
Total current assets	428,219	436,837
Long-term marketable securities	24,493	32,634
Property and equipment, net	7,038	8,596
Deferred tax assets	345	345
Operating lease, right-of-use assets	6,972	7,020
Restricted cash	608	608
Other long-term assets	92	92
Total assets	467,767	486,132
Current liabilities:
Accounts payable	5,699	5,737
Accrued expenses and other current liabilities	15,744	14,159
Operating lease liabilities	5,175	4,261
Total current liabilities	26,618	24,157
Operating lease liabilities, net of current portion	2,644	3,838
Series 1 nonconvertible preferred stock	1,479	1,479
Other long-term liabilities	994	1,078
Total liabilities	31,735	30,552
Commitments and contingencies (Note 11)
Stockholders' equity:
Common stock; $0.01 par value per share, 100,000 shares authorized; 20,185 and 20,077 shares issued and outstanding at March 31, 2021 and September 30, 2020, respectively	202	201
Additional paid-in capital	338,576	326,963
Accumulated other comprehensive income	55	844
Retained earnings	97,199	127,572
Total stockholders' equity	436,032	455,580
Total liabilities and stockholders' equity	$ 467,767	$ 486,132

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - $ / shares	Mar. 31, 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	20,185,000	20,077,000
Common stock, shares outstanding	20,185,000	20,077,000

Consolidated Statements of Oper

Consolidated Statements of Operations - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2021	Mar. 31, 2020
Income Statement [Abstract]
Royalty revenue	$ 20,132	$ 27,619	$ 51,875	$ 80,189
Type Of Revenue Extensible List	us-gaap:RoyaltyMember	us-gaap:RoyaltyMember	us-gaap:RoyaltyMember	us-gaap:RoyaltyMember
Operating expenses:
Research and development	$ 41,506	$ 32,610	$ 78,171	$ 65,388
General and administrative	8,326	6,884	15,703	13,805
Total operating expenses	49,832	39,494	93,874	79,193
Income (loss) from operations	(29,700)	(11,875)	(41,999)	996
Other income (expense):
Other income (expense), net	545	1,950	1,222	4,026
Total other income (expense), net	545	1,950	1,222	4,026
Income (loss) before income taxes	(29,155)	(9,925)	(40,777)	5,022
Income tax benefit	7,110	3,920	10,404	2,416
Net income (loss)	$ (22,045)	$ (6,005)	$ (30,373)	$ 7,438
Net income (loss) per share:
Basic	$ (1.09)	$ (0.30)	$ (1.51)	$ 0.37
Diluted	$ (1.09)	$ (0.30)	$ (1.51)	$ 0.36
Weighted average shares outstanding:
Basic	20,171	19,922	20,131	19,836
Diluted	20,171	19,922	20,131	20,692

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Income (Loss) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2021	Mar. 31, 2020
Statement Of Income And Comprehensive Income [Abstract]
Net income (loss)	$ (22,045)	$ (6,005)	$ (30,373)	$ 7,438
Other comprehensive income (loss):
Net unrealized gains (losses) on marketable securities, net of tax of $0, $119, $0 and $147	(350)	374	(789)	462
Total other comprehensive income (loss), net of tax	(350)	374	(789)	462
Comprehensive income (loss)	$ (22,395)	$ (5,631)	$ (31,162)	$ 7,900

Consolidated Statements of Co_2

Consolidated Statements of Comprehensive Income (Loss) (Parenthetical) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2021	Mar. 31, 2020
Statement Of Income And Comprehensive Income [Abstract]
Net unrealized gains (losses) on marketable securities, tax	$ 0	$ 119	$ 0	$ 147

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	462
Net income (loss)	7,438
Ending Balance at Mar. 31, 2020	485,991	$ 200	314,005	608	171,178
Ending Balance, Shares at Mar. 31, 2020		19,986
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
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	76
Other comprehensive income (loss), net of tax	$ (789)
Net income (loss)	(30,373)
Ending Balance at Mar. 31, 2021	436,032	$ 202	338,576	55	97,199
Ending Balance, Shares at Mar. 31, 2021		20,185
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

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	6 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Cash flows from operating activities
Net income (loss)	$ (30,373)	$ 7,438
Adjustments to reconcile net income to net cash provided by operating activities:
Stock-based compensation expense	10,163	10,076
Depreciation and amortization expense	1,705	1,819
Deferred income taxes		(1,224)
Premium paid on marketable securities	(1,238)	(2,398)
(Accretion) amortization of (discount) premium on marketable securities	956	(379)
Change in operating assets and liabilities:
Accounts receivable	3,360	23,694
Prepaid expenses and other current assets	(5,444)	(4,536)
Operating lease, right-of-use assets	2,565	1,311
Accounts payable	15	(731)
Accrued expenses	1,703	(5,585)
Operating lease liabilities	(2,797)	(1,484)
Other long-term liabilities	(84)	(964)
Net cash provided by (used in) operating activities	(19,469)	27,037
Cash flows from investing activities
Purchase of marketable securities	(171,586)	(171,884)
Proceeds from maturities and sale of marketable securities	179,917	163,273
Purchase of property and equipment	(318)	(842)
Net cash provided by (used in) investing activities	8,013	(9,453)
Cash flows from financing activities
Proceeds from exercise of stock options	1,985	7,022
Payments for settlement of share-based awards	(534)	(1,498)
Net cash provided by financing activities	1,451	5,524
Net increase (decrease) in cash, cash equivalents and restricted cash	(10,005)	23,108
Cash, cash equivalents and restricted cash at beginning of period	87,739	51,838
Cash, cash equivalents and restricted cash at end of period	77,734	74,946
Supplemental disclosure of non-cash operating and investing information:
Purchases of fixed assets included in accounts payable and accrued expenses	17	109
Operating lease liabilities arising from obtaining right-of-use assets	$ 2,517	$ 1,997

Nature of the Business and Basi

Nature of the Business and Basis of Presentation	6 Months Ended
	Mar. 31, 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 March 31, 2021 and for the three and six months ended March 31, 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 March 31, 2021 and results of operations for the three and six months ended March 31, 2021 and 2020 and cash flows for the six months ended March 31, 2021 and 2020, have been made. The results of operations for the three and six months ended March 31, 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	6 Months Ended
	Mar. 31, 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. March 31, 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	6 Months Ended
	Mar. 31, 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 March 31, 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 March 31, 2021 Using: Level 1 Level 2 Level 3 Total (in thousands) Assets: Cash equivalents: Money market funds $ 76,137 $ — $ — $ 76,137 Marketable securities: U.S. Treasury notes 51,556 — — 51,556 Commercial paper — 153,459 — 153,459 Corporate bonds — 118,299 — 118,299 $ 127,693 $ 271,758 $ — $ 399,451 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 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 During the six months ended March 31, 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 March 31, 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, March 31, 2021 $ 1,479

Marketable Securities

Marketable Securities	6 Months Ended
	Mar. 31, 2021
Investments Debt And Equity Securities [Abstract]
Marketable Securities	4. Marketable Securities As of March 31, 2021 and September 30, 2020, the fair value of available-for-sale marketable securities, by type of security, was as follows: March 31, 2021 Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Credit Losses Fair Value (in thousands) Commercial paper $ 153,459 $ — $ — $ — $ 153,459 Corporate bonds 118,001 339 (41 ) — 118,299 U.S. Treasury notes 51,414 142 — — 51,556 $ 322,874 $ 481 $ (41 ) $ — $ 323,314 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 March 31, 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 $24,493 and $32,634, respectively.

Accrued Expenses and Other Long

Accrued Expenses and Other Long-Term Liabilities	6 Months Ended
	Mar. 31, 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 March 31, 2021 and September 30, 2020: March 31, September 2021 2020 (in thousands) Accrued expenses: Accrued research and development expenses $ 7,031 $ 5,407 Accrued pharmaceutical drug manufacturing 4,404 2,885 Accrued payroll and related expenses 2,592 4,777 Accrued professional fees 684 478 Accrued other 1,033 612 $ 15,744 $ 14,159 Other long-term liabilities: Uncertain tax positions $ 686 $ 788 Asset retirement obligation 308 290 $ 994 $ 1,078

AbbVie Collaboration

AbbVie Collaboration	6 Months Ended
	Mar. 31, 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 $1,076,000 through March 31, 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	6 Months Ended
	Mar. 31, 2021
Debt Disclosure [Abstract]
Series 1 Nonconvertible Preferred Stock	7. Series 1 Nonconvertible Preferred Stock As of March 31, 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	6 Months Ended
	Mar. 31, 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 March 31, 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 805 44.76 Exercised (76 ) 26.27 Forfeited (105 ) 66.81 Outstanding as of March 31, 2021 3,886 $ 48.77 6.8 $ 29,478 Options vested and expected to vest as of March 31, 2021 3,886 $ 48.77 6.8 $ 29,478 Options exercisable as of March 31, 2021 2,312 $ 44.40 5.4 $ 25,801 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 March 31, 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 vest 50% in three years and 50% in four years, provided 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. These units became fully vested during the three months ended December 31, 2020. In November 2020, the Company awarded additional restricted stock units to its employees, which vest in equal annual installments over four years, provided 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 March 31, 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 (1 ) 37.68 Unvested at March 31, 2021 122 $ 43.57 Stock-Based Compensation Expense During the three and six months ended March 31, 2021 and 2020, the Company recognized the following stock-based compensation expense: Three Months ended Six Months Ended March 31, March 31, 2021 2020 2021 2020 (in thousands) Research and development $ 2,536 $ 2,688 $ 4,955 $ 5,180 General and administrative 2,744 2,289 5,208 4,896 $ 5,280 $ 4,977 $ 10,163 $ 10,076 Three Months ended Six Months Ended March 31, March 31, 2021 2020 2021 2020 (in thousands) Stock options $ 4,514 $ 4,441 $ 8,863 $ 8,777 Performance stock units — 16 — 259 rTSRUs 444 359 721 721 Restricted stock units 322 161 579 319 $ 5,280 $ 4,977 $ 10,163 $ 10,076 During the three months ended December 31, 2019, 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. During the three months ended no such units vested. As of March 31, 2021, the Company had an aggregate of $54,137 of unrecognized stock-based compensation cost, which is expected to be recognized over a weighted average period of 2.5 years.

Net Income (Loss) Per Share

Net Income (Loss) Per Share	6 Months Ended
	Mar. 31, 2021
Earnings Per Share [Abstract]
Net Income (Loss) Per Share	9. Net Income (Loss) Per Share Basic and diluted net income (loss) per share attributable to common stockholders was calculated as follows for the three and six months ended March 31, 2021 and 2020: Three Months Ended Six Months Ended March 31, March 31, 2021 2020 2021 2020 (in thousands, except per share data) Basic net income (loss) per share: Numerator: Net income (loss) $ (22,045 ) $ (6,005 ) $ (30,373 ) $ 7,438 Denominator: Weighted average common shares outstanding —basic 20,171 19,922 20,131 19,836 Net income (loss) per share common share—basic $ (1.09 ) $ (0.30 ) $ (1.51 ) $ 0.37 Diluted net income (loss) per share: Numerator: Net income (loss) $ (22,045 ) $ (6,005 ) $ (30,373 ) $ 7,438 Denominator: Weighted average common shares outstanding —basic 20,171 19,922 20,131 19,836 Dilutive effect of common stock equivalents — — — 856 Weighted average common shares outstanding —diluted 20,171 19,922 20,131 20,692 Net income (loss) per share common share—diluted $ (1.09 ) $ (0.30 ) $ (1.51 ) $ 0.36 Anti-dilutive common stock equivalents excluded from above 4,268 3,714 4,307 2,457 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	6 Months Ended
	Mar. 31, 2021
Income Tax Disclosure [Abstract]
Income Taxes	10. Income Taxes For the three months ended March 31, 2021 and 2020, the Company recorded an income tax benefit of $7,110 and $3,920, respectively, both of which were attributable to the Company’s domestic operations. The Company recorded an income tax benefit during the three and six months ended March 31, 2021 due to the Company’s ability and intent to carryback its current year tax loss under the CARES Act”) which . As of March 31, 2021 and September 30, 2020, the Company recorded prepaid federal income taxes of $18,804 and $10,487, respectively. 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 the prior 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, 2017 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 $686 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 six months ended March 31, 2021 . As of March 31, 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 continues to progress its wholly-owned research and development programs and its declining royalty revenues from its Collaboration Agreement with AbbVie.

Commitments and Contingencies

Commitments and Contingencies	6 Months Ended
	Mar. 31, 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 March 31, 2021.

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	6 Months Ended
	Mar. 31, 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. March 31, 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)	6 Months Ended
	Mar. 31, 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 March 31, 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 March 31, 2021 Using: Level 1 Level 2 Level 3 Total (in thousands) Assets: Cash equivalents: Money market funds $ 76,137 $ — $ — $ 76,137 Marketable securities: U.S. Treasury notes 51,556 — — 51,556 Commercial paper — 153,459 — 153,459 Corporate bonds — 118,299 — 118,299 $ 127,693 $ 271,758 $ — $ 399,451 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 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 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 March 31, 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, March 31, 2021 $ 1,479

Marketable Securities (Tables)

Marketable Securities (Tables)	6 Months Ended
	Mar. 31, 2021
Investments Debt And Equity Securities [Abstract]
Fair Value of Available-for-Sale Marketable Securities by Type of Security	As of March 31, 2021 and September 30, 2020, the fair value of available-for-sale marketable securities, by type of security, was as follows: March 31, 2021 Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Credit Losses Fair Value (in thousands) Commercial paper $ 153,459 $ — $ — $ — $ 153,459 Corporate bonds 118,001 339 (41 ) — 118,299 U.S. Treasury notes 51,414 142 — — 51,556 $ 322,874 $ 481 $ (41 ) $ — $ 323,314 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)	6 Months Ended
	Mar. 31, 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 March 31, 2021 and September 30, 2020: March 31, September 2021 2020 (in thousands) Accrued expenses: Accrued research and development expenses $ 7,031 $ 5,407 Accrued pharmaceutical drug manufacturing 4,404 2,885 Accrued payroll and related expenses 2,592 4,777 Accrued professional fees 684 478 Accrued other 1,033 612 $ 15,744 $ 14,159 Other long-term liabilities: Uncertain tax positions $ 686 $ 788 Asset retirement obligation 308 290 $ 994 $ 1,078

Stock-Based Awards (Tables)

Stock-Based Awards (Tables)	6 Months Ended
	Mar. 31, 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 March 31, 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 805 44.76 Exercised (76 ) 26.27 Forfeited (105 ) 66.81 Outstanding as of March 31, 2021 3,886 $ 48.77 6.8 $ 29,478 Options vested and expected to vest as of March 31, 2021 3,886 $ 48.77 6.8 $ 29,478 Options exercisable as of March 31, 2021 2,312 $ 44.40 5.4 $ 25,801
Summary of Restricted Stock Unit Activity	The following table summarizes the restricted stock unit activity for the year-to-date period ending March 31, 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 (1 ) 37.68 Unvested at March 31, 2021 122 $ 43.57
Stock-Based Compensation Expense	During the three and six months ended March 31, 2021 and 2020, the Company recognized the following stock-based compensation expense: Three Months ended Six Months Ended March 31, March 31, 2021 2020 2021 2020 (in thousands) Research and development $ 2,536 $ 2,688 $ 4,955 $ 5,180 General and administrative 2,744 2,289 5,208 4,896 $ 5,280 $ 4,977 $ 10,163 $ 10,076 Three Months ended Six Months Ended March 31, March 31, 2021 2020 2021 2020 (in thousands) Stock options $ 4,514 $ 4,441 $ 8,863 $ 8,777 Performance stock units — 16 — 259 rTSRUs 444 359 721 721 Restricted stock units 322 161 579 319 $ 5,280 $ 4,977 $ 10,163 $ 10,076
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 March 31, 2021 111 49.31 111 $ 31.26

Net Income (Loss) Per Share (Ta

Net Income (Loss) Per Share (Tables)	6 Months Ended
	Mar. 31, 2021
Earnings Per Share [Abstract]
Basic and Diluted Net Income (Loss) Per Share Attributable to Common Stockholders	Basic and diluted net income (loss) per share attributable to common stockholders was calculated as follows for the three and six months ended March 31, 2021 and 2020: Three Months Ended Six Months Ended March 31, March 31, 2021 2020 2021 2020 (in thousands, except per share data) Basic net income (loss) per share: Numerator: Net income (loss) $ (22,045 ) $ (6,005 ) $ (30,373 ) $ 7,438 Denominator: Weighted average common shares outstanding —basic 20,171 19,922 20,131 19,836 Net income (loss) per share common share—basic $ (1.09 ) $ (0.30 ) $ (1.51 ) $ 0.37 Diluted net income (loss) per share: Numerator: Net income (loss) $ (22,045 ) $ (6,005 ) $ (30,373 ) $ 7,438 Denominator: Weighted average common shares outstanding —basic 20,171 19,922 20,131 19,836 Dilutive effect of common stock equivalents — — — 856 Weighted average common shares outstanding —diluted 20,171 19,922 20,131 20,692 Net income (loss) per share common share—diluted $ (1.09 ) $ (0.30 ) $ (1.51 ) $ 0.36 Anti-dilutive common stock equivalents excluded from above 4,268 3,714 4,307 2,457

Nature of the Business and Ba_2

Nature of the Business and Basis of Presentation - Additional Information (Detail)	6 Months Ended
	Mar. 31, 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	Mar. 31, 2021	Sep. 30, 2020
Assets:
Marketable securities	$ 323,314	$ 332,152
Assets, Fair Value Disclosure, Total	399,451	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	127,693	175,710
Level 2 [Member]
Assets:
Assets, Fair Value Disclosure, Total	271,758	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	76,137	81,502
Money Market Funds [Member] | Level 1 [Member]
Assets:
Cash equivalents	76,137	81,502
Corporate Bonds [Member]
Assets:
Marketable securities	118,299	144,035
Corporate Bonds [Member] | Level 2 [Member]
Assets:
Marketable securities	118,299	144,035
Commercial Paper [Member]
Assets:
Marketable securities	153,459	93,909
Commercial Paper [Member] | Level 2 [Member]
Assets:
Marketable securities	153,459	93,909
U.S. Treasury Notes [Member]
Assets:
Marketable securities	51,556	94,208
U.S. Treasury Notes [Member] | Level 1 [Member]
Assets:
Marketable securities	$ 51,556	$ 94,208

Fair Value of Financial Asset_4

Fair Value of Financial Assets and Liabilities - Additional Information (Detail) - USD ($)	6 Months Ended
	Mar. 31, 2021	Mar. 31, 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]	Mar. 31, 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	Mar. 31, 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	Mar. 31, 2021	Sep. 30, 2020
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 322,874	$ 330,923
Gross Unrealized Gains	481	1,243
Gross Unrealized Losses	(41)	(14)
Fair Value	323,314	332,152
Commercial Paper [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	153,459	93,909
Fair Value	153,459	93,909
Corporate Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	118,001	143,274
Gross Unrealized Gains	339	775
Gross Unrealized Losses	(41)	(14)
Fair Value	118,299	144,035
U.S. Treasury Notes [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	51,414	93,740
Gross Unrealized Gains	142	468
Fair Value	$ 51,556	$ 94,208

Marketable Securities - Additio

Marketable Securities - Additional Information (Detail) - USD ($) $ in Thousands	6 Months Ended
	Mar. 31, 2021	Sep. 30, 2020
Schedule of Available-for-sale Securities [Line Items]
Long-term marketable securities	$ 24,493	$ 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	Mar. 31, 2021	Sep. 30, 2020
Accrued expenses:
Accrued research and development expenses	$ 7,031	$ 5,407
Accrued pharmaceutical drug manufacturing	4,404	2,885
Accrued payroll and related expenses	2,592	4,777
Accrued professional fees	684	478
Accrued other	1,033	612
Accrued expenses	15,744	14,159
Other long-term liabilities:
Uncertain tax positions	686	788
Asset retirement obligation	308	290
Other long-term liabilities	$ 994	$ 1,078

AbbVie Collaboration - Addition

AbbVie Collaboration - Additional Information (Detail) - AbbVie [Member] $ in Thousands	6 Months Ended
	Mar. 31, 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	$ 1,076,000
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	Mar. 31, 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) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	6 Months Ended	12 Months Ended
	Mar. 31, 2021	Sep. 30, 2019	Sep. 30, 2020
Options
Outstanding as of beginning of period	3,262
Granted	805
Exercised	(76)
Forfeited	(105)
Outstanding as of end of period	3,886
Options vested and expected to vest as of end of period	3,886
Options exercisable as of end of period	2,312
Weighted Average Exercise Price
Outstanding	$ 49.82
Granted	44.76
Exercised	26.27
Forfeited	66.81
Outstanding	48.77
Options vested and expected to vest as of end of period	48.77
Options exercisable as of end of period	$ 44.40
Weighted Average Remaining Contractual Term
Outstanding as of end of period	6 years 9 months 18 days	6 years 6 months
Options vested and expected to vest as of end period	6 years 9 months 18 days
Options exercisable as of end of period	5 years 4 months 24 days
Aggregate Intrinsic Value
Aggregate Intrinsic Value	$ 29,478		$ 21,860
Options vested and expected to vest as of March 31, 2021	29,478
Options exercisable as of end of period	$ 25,801

Stock-Based Awards - Additional

Stock-Based Awards - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Dec. 31, 2020	Dec. 31, 2016	Mar. 31, 2021
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period	4 years
Aggregate of unrecognized stock-based compensation cost			$ 54,137
Weighted average recognition period			2 years 6 months
Restricted Stock Units [Member] | Tranche One [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting percentage		50.00%
Vesting period		3 years
Restricted Stock Units [Member] | Tranche Two [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting percentage		50.00%
Vesting period		4 years
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	6 Months Ended
	Mar. 31, 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	6 Months Ended
	Mar. 31, 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	(1)
Unvested, ending balance | shares	122
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	37.68
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		6 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2021	Mar. 31, 2020
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	$ 5,280	$ 4,977	$ 10,163	$ 10,076
Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	4,514	4,441	8,863	8,777
Performance Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense		16		259
rTSRUs [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	444	359	721	721
Restricted Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	322	161	579	319
Research and Development [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	2,536	2,688	4,955	5,180
General and Administrative [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	$ 2,744	$ 2,289	$ 5,208	$ 4,896

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				6 Months Ended
	Mar. 31, 2021	Dec. 31, 2020	Mar. 31, 2020	Dec. 31, 2019	Mar. 31, 2021	Mar. 31, 2020
Basic net income (loss) per share:
Net income (loss)	$ (22,045)	$ (8,328)	$ (6,005)	$ 13,443	$ (30,373)	$ 7,438
Weighted average common shares outstanding —basic	20,171		19,922		20,131	19,836
Net income (loss) per share common share—basic	$ (1.09)		$ (0.30)		$ (1.51)	$ 0.37
Diluted net income (loss) per share:
Net income (loss)	$ (22,045)	$ (8,328)	$ (6,005)	$ 13,443	$ (30,373)	$ 7,438
Basic	20,171		19,922		20,131	19,836
Dilutive effect of common stock equivalents						856
Weighted average common shares outstanding —diluted	20,171		19,922		20,131	20,692
Net income (loss) per share common share—diluted	$ (1.09)		$ (0.30)		$ (1.51)	$ 0.36
Anti-dilutive common stock equivalents excluded from above	4,268		3,714		4,307	2,457

Income Taxes - Additional Infor

Income Taxes - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2021	Mar. 31, 2020	Sep. 30, 2020
Income Tax [Line Items]
Income tax benefit	$ 7,110	$ 3,920	$ 10,404	$ 2,416
Unrecognized tax benefits	686		$ 686		$ 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.
Federal [Member]
Income Tax [Line Items]
Prepaid federal income taxes	$ 18,804		$ 18,804		$ 10,487