Enanta Pharmaceuticals (ENTA) 10-Q 9 Feb 18 2018 Q1 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	3 Months Ended
	Dec. 31, 2017	Feb. 01, 2018
Document And Entity Information [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Dec. 31, 2017
Document Fiscal Year Focus	2,018
Document Fiscal Period Focus	Q1
Trading Symbol	ENTA
Entity Registrant Name	ENANTA PHARMACEUTICALS INC
Entity Central Index Key	1,177,648
Current Fiscal Year End Date	--09-30
Entity Filer Category	Accelerated Filer
Entity Common Stock, Shares Outstanding		19,160,667

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2017	Sep. 30, 2017
Current assets:
Cash and cash equivalents	$ 68,053	$ 65,675
Short-term marketable securities	152,389	157,994
Accounts receivable	23,109	10,614
Prepaid expenses and other current assets	4,075	3,536
Total current assets	247,626	237,819
Property and equipment, net	7,870	8,049
Long-term marketable securities	77,047	70,038
Deferred tax assets	7,568	10,123
Restricted cash	608	608
Total assets	340,719	326,637
Current liabilities:
Accounts payable	3,268	3,714
Accrued expenses and other current liabilities	5,697	7,970
Income taxes payable	10,257	9,298
Total current liabilities	19,222	20,982
Warrant liability		807
Series 1 nonconvertible preferred stock	1,528	762
Other long-term liabilities	2,390	2,410
Total liabilities	23,140	24,961
Commitments and contingencies (Note 11)
Stockholders' equity:
Common stock; $0.01 par value per share, 100,000 shares authorized; 19,150 and 19,120 shares issued and outstanding at December 31, 2017 and September 30, 2017, respectively	191	191
Additional paid-in capital	260,752	256,241
Accumulated other comprehensive loss	(458)	(112)
Retained earnings	57,094	45,356
Total stockholders' equity	317,579	301,676
Total liabilities and stockholders' equity	$ 340,719	$ 326,637

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - $ / shares	Dec. 31, 2017	Sep. 30, 2017
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	19,150,000	19,120,000
Common stock, shares outstanding	19,150,000	19,120,000

Consolidated Statements of Oper

Consolidated Statements of Operations - USD ($) shares in Thousands, $ in Thousands	3 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Revenue
Royalties	$ 23,109	$ 10,417
Milestones	15,000
Total revenue	38,109	10,417
Operating expenses:
Research and development	17,962	12,526
General and administrative	5,770	4,937
Total operating expenses	23,732	17,463
Income (loss) from operations	14,377	(7,046)
Other income (expense):
Interest income	928	549
Interest expense	(9)	(12)
Change in fair value of warrant liability and Series 1 nonconvertible preferred stock	41	(13)
Total other income (expense), net	960	524
Income (loss) before income taxes	15,337	(6,522)
Income tax (expense) benefit	(3,644)	1,542
Net income (loss)	$ 11,693	$ (4,980)
Net income (loss) per share:
Basic	$ 0.61	$ (0.26)
Diluted	$ 0.59	$ (0.26)
Weighted average shares outstanding:
Basic	19,130	19,038
Diluted	19,918	19,038

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Income (Loss) - USD ($) $ in Thousands	3 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Statement Of Income And Comprehensive Income [Abstract]
Net income (loss)	$ 11,693	$ (4,980)
Other comprehensive loss:
Net unrealized losses on marketable securities, net of tax of ($107) and ($63)	(346)	(104)
Total other comprehensive loss	(346)	(104)
Comprehensive income (loss)	$ 11,347	$ (5,084)

Consolidated Statements of Com6

Consolidated Statements of Comprehensive Income (Loss) (Parenthetical) - USD ($) $ in Thousands	3 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Statement Of Income And Comprehensive Income [Abstract]
Net unrealized losses on marketable securities, tax	$ (107)	$ (63)

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Cash flows from operating activities
Net income (loss)	$ 11,693	$ (4,980)
Adjustments to reconcile net income (loss) to net cash provided by operating activities:
Stock-based compensation expense	4,120	3,267
Depreciation and amortization expense	587	493
Deferred income taxes	2,662	(1,910)
Income tax benefit from exercise of stock options	245
Premium on marketable securities	(1)	(324)
Amortization of premium on marketable securities	88	188
Change in fair value of warrant liability and Series 1 nonconvertible preferred stock	(41)	13
Change in operating assets and liabilities:
Accounts receivable	(12,495)	2,424
Prepaid expenses and other current assets	(539)	4,941
Accounts payable	(129)	(1,290)
Accrued expenses	(2,494)	(10)
Income taxes payable	714
Other long-term liabilities	(1)	333
Net cash provided by operating activities	4,409	3,145
Cash flows from investing activities
Purchase of property and equipment	(504)	(953)
Purchase of marketable securities	(54,710)	(73,671)
Proceeds from maturities and sales of marketable securities	52,766	75,489
Net cash provided by (used in) investing activities	(2,448)	865
Cash flows from financing activities
Proceeds from exercise of stock options	436	49
Payments of capital lease obligations	(19)	(18)
Net cash provided by financing activities	417	31
Net increase in cash and cash equivalents	2,378	4,041
Cash and cash equivalents at beginning of period	65,675	16,577
Cash and cash equivalents at end of period	68,053	20,618
Supplemental disclosure of cash flow information:
Cash paid for income taxes	$ 13	$ 1,018

Nature of the Business and Basi

Nature of the Business and Basis of Presentation	3 Months Ended
	Dec. 31, 2017
Accounting Policies [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 create small molecule drugs primarily 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 and marketed as part of AbbVie’s new direct-acting antiviral (DAA) regimen under the tradenames MAVYRET™ (U.S.) or MAVIRET™ (ex-U.S.) (glecaprevir/pibrentasvir) for the treatment of chronic hepatitis C virus, or HCV. The other protease inhibitor under its HCV collaboration is part of AbbVie’s initial DAA regimens for the treatment of chronic HCV marketed under the tradenames VIEKIRA PAK ® ® Royalties from the Company’s AbbVie collaboration and its existing financial resources provide funding to support its wholly owned research and development efforts , which are currently focused on the following disease targets The Company is subject to 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 regulations and the need to obtain additional financing. 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. Unaudited Interim Financial Information The consolidated balance sheet at September 30, 2017 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 December 31, 2017 and for the three months ended December 31, 2017 and 2016 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, 2017. 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 December 31, 2017 and results of operations for the three months ended December 31, 2017 and 2016 and cash flows for the three months ended December 31, 2017 and 2016, have been made. The results of operations for the three months ended December 31, 2017 are not necessarily indicative of the results of operations that may be expected for subsequent quarters or the year ending September 30, 2018. The accompanying consolidated financial statements have been prepared in conformity with GAAP. All dollar 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	3 Months Ended
	Dec. 31, 2017
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, 2017. Other than the adoption of ASU 2016-09 as of October 1, 2017, there were no other significant changes to the Company’s Significant Accounting Policies during the quarter. 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 of separate units of accounting and best estimate of selling price of those units of accounting within its revenue arrangements; valuation of stock-based awards; and the accounting for income taxes, including uncertain tax positions and the valuation of net deferred tax assets. . Recently Issued Accounting Pronouncements In March 2016, the FASB issued ASU No. 2016-09, Improvements to Employee Share-Based Payment Accounting (“ASU 2016-09”), which intends to simplify several aspects of accounting for share-based payment transactions, including the income tax consequences, classification of awards as either equity or liabilities, a choice to recognize gross stock compensation expense with actual forfeitures recognized as they occur, as well as certain classifications on the statement of cash flows. This amendment is effective for the Company in the fiscal year beginning October 1, 2017. As a result of the adoption this quarter, the Company changed its forfeiture rate policy to recognize forfeitures as they occur. Upon adoption, the cumulative impact of this change in policy on retained earnings and deferred tax assets in the consolidated balance sheet was not material. In addition, the consolidated statements of cash flows will present excess tax benefits, if any, as part of cash flows from operating activities. The Company elected to adopt this change on a prospective basis and, therefore, excess tax benefits from prior periods in the statement of cash flow were not restated. The adoption of the standard is also expected to create variability in the consolidated statements of operations in years in which the Company is expected to have taxable income, as the tax consequences of settled share-based payments will be recognized in income tax expense when share-based payment awards are settled. In May 2014, the FASB issued ASU No. 2014-09, Revenue from Contracts with Customers (Topic 606) (“ASU 2014-09”) which supersedes all existing revenue recognition requirements, including most industry-specific guidance. The new standard requires a company to recognize revenue when it transfers goods or services to customers in an amount that reflects the consideration that the company expects to receive for those goods or services. The FASB has continued to issue accounting standards updates to clarify and provide implementation guidance related to Revenue from Contracts with Customers, including ASU 2016-08 , Revenue from Contract with Customers: Principal versus Agent Considerations , ASU 2016-10, Revenue from Contracts with Customers: Identifying Performance Obligations and Licensing , and ASU 2016-12, Revenue from Contracts with Customers: Narrow-Scope Improvements and Practical Expedients. These amendments address a number of areas, including an entity’s identification of its performance obligations in a contract, collectibility, non-cash consideration, presentation of sales tax and an entity’s evaluation of the nature of its promise to grant a license of intellectual property and whether or not that revenue is recognized over time or at a point in time. The new guidance must be adopted using either a modified retrospective approach or a full retrospective approach for all periods presented. Under the modified retrospective method, the cumulative effect of applying the new standard would be recognized at the adoption date in retained earnings on the consolidated balance sheet. Under the full retrospective approach, the new standard would be applied to each prior reporting period presented. These new standards will be effective for the Company beginning October 1, 2018. Currently, the Company has only one revenue-generating contract – the AbbVie Agreement. The Company has completed its substantial performance obligations under the contract and is eligible to earn annually tiered per-product royalties on the portion of AbbVie’s net sales of HCV regimens allocable to the protease inhibitor in the regimen. The Company is in process of determining the method of adoption but under either method, the impact of adoption is not expected to have a material impact on the Company’s consolidated financial statements as presently, the AbbVie Agreement is the only revenue-generating arrangement outstanding, and all performance obligations under the agreement have been achieved. In November 2016, the FASB issued ASU No. 2016-18, Statement of Cash Flows (Topic 230): Restricted Cash (“ASU 2016-18”) that changes the presentation of restricted cash and cash equivalents on the statement of cash flows. Restricted cash and restricted cash equivalents will be included with cash and cash equivalents when reconciling the beginning-of-period and end-of-period total amounts shown on the statement of cash flows. This amendment is effective for the Company in the fiscal year beginning October 1, 2018, but early adoption is permissible. Upon adoption, the Company will adjust the presentation of the statement of cash flows to include restricted cash related to an outstanding letter of credit collateralized by a money market fund of $608 so that it is included in the beginning balance of cash and cash equivalents. In May 2017, the FASB issued ASU No. 2017-09, Compensation—Stock Compensation (Topic 718) (“ASU 2017-09”) which This amendment is effective for the Company in the fiscal year beginning October 1, 2018, but early adoption is permissible. In February 2016, the FASB issued ASU No. 2016-02, Leases (“ASU 2016-02”), which will replace the existing guidance in ASC 840, “Leases.” The updated standard aims to increase transparency and comparability among organizations by requiring lessees to recognize leased assets and leased liabilities on the consolidated balance sheets and requiring disclosure of key information about leasing arrangements. This amendment is effective for the Company in the fiscal year beginning October 1, 2019, but early adoption is permissible. The Company is currently evaluating the potential impact that ASU 2016-02 may have on its financial position and results of operations. In March 2017, the FASB issued ASU No. 2017-08, Receivables—Nonrefundable Fees and Other Costs (Subtopic 310-20): Premium Amortization on Purchased Callable Debt Securities (“ASU 2017-08”) which requires companies to amend the amortization period for premiums on debt securities with explicit call features to be the earliest call date rather than through the contractual life of the debt instrument. This amendment aims to more closely align the recognition of interest income with the manner in which market participants price such instruments. This amendment is effective for the Company in the fiscal year beginning October 1, 2019, but early adoption is permissible. The Company is currently evaluating the potential impact that ASU 2017-08 may have on its financial position and results of operations. In June 2016, the FASB issued ASU No. 2016-13, Financial Instruments—Credit Losses (“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. This amendment is effective for the Company in the fiscal year beginning October 1, 2020. The Company is currently evaluating the potential impact that ASU 2016-13 may have on its financial position and results of operations. 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	3 Months Ended
	Dec. 31, 2017
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 December 31, 2017 and September 30, 2017 and indicate the fair value hierarchy of the valuation inputs utilized to determine such fair value: Fair Value Measurements at December 31, 2017 Using: Level 1 Level 2 Level 3 Total (in thousands) Assets: Cash equivalents: Money market funds $ 36,702 $ — $ — $ 36,702 U.S. Treasury notes — 5,990 — 5,990 Commercial paper — 8,984 — 8,984 Marketable securities: U.S. Treasury notes 51,698 — — 51,698 Corporate bonds — 154,286 — 154,286 Commercial paper — 23,452 — 23,452 $ 88,400 $ 192,712 $ — $ 281,112 Liabilities: Warrant liability $ — $ — $ — $ — Series 1 nonconvertible preferred stock — — 1,528 1,528 $ — $ — $ 1,528 $ 1,528 Fair Value Measurements at September 30, 2017 Using: Level 1 Level 2 Level 3 Total (in thousands) Assets: Cash equivalents: Money market funds $ 19,863 $ — $ — $ 19,863 Commercial paper — 29,756 — 29,756 Corporate bonds — 3,000 — 3,000 Marketable securities: U.S. Treasury notes 60,843 — — 60,843 Corporate bonds — 150,731 — 150,731 Commercial paper — 12,458 — 12,458 U.S. Agency bonds — 4,000 — 4,000 $ 80,706 $ 199,945 $ — $ 280,651 Liabilities: Warrant liability $ — $ — $ 807 $ 807 Series 1 nonconvertible preferred stock — — 762 762 $ — $ — $ 1,569 $ 1,569 During the three months ended December 31, 2017 and 2016, there were no transfers between Level 1, Level 2 and Level 3. As of September 30, 2017, the Company’s warrant liability was comprised of the value of warrants for the purchase of its Series 1 nonconvertible preferred stock. These warrants were financial instruments that might have required a transfer of assets because of the liquidation features and were therefore recorded as liabilities and measured at fair value. These warrants expired on October 4, 2017, and are therefore no longer outstanding. The outstanding shares of Series 1 nonconvertible preferred stock are also 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 warrant liability and 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 warrant liability and Series 1 nonconvertible preferred stock using probability-weighted discounted cash flow include the following significant unobservable inputs: Range (Weighted Average) December 31, September 30, Unobservable Input 2017 2017 Warrant liability and Series 1 nonconvertible preferred stock Probabilities of payout 0%-65% 0%-65% Discount rate 5.25% 5.25% The following table provides a rollforward of the aggregate fair values of the Company’s warrants for the purchase of Series 1 nonconvertible preferred stock and the outstanding Series 1 nonconvertible preferred stock for which fair value is determined by Level 3 inputs: Warrant Liability Series 1 Nonconvertible Preferred Stock Balance, September 30, 2017 $ 807 $ 762 Warrants exercised (766 ) 766 Warrants expired (41 ) — Balance, December 31, 2017 $ — $ 1,528

Marketable Securities

Marketable Securities	3 Months Ended
	Dec. 31, 2017
Investments Debt And Equity Securities [Abstract]
Marketable Securities	4. Marketable Securities As of December 31, 2017 and September 30, 2017, the fair value of available-for-sale marketable securities, by type of security, was as follows: December 31, 2017 Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value (in thousands) Corporate bonds $ 154,778 $ — $ (492 ) $ 154,286 U.S. Treasury notes 51,838 — (140 ) 51,698 Commercial paper 23,452 — — 23,452 $ 230,068 $ — $ (632 ) $ 229,436 September 30, 2017 Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value (in thousands) Corporate bonds $ 150,841 $ 9 $ (119 ) $ 150,731 U.S. Treasury notes 60,908 — (65 ) 60,843 Commercial paper 12,458 — — 12,458 U.S. Agency bonds 4,004 — (4 ) 4,000 $ 228,211 $ 9 $ (188 ) $ 228,032 As of December 31, 2017, marketable securities consisted of short-term marketable securities, which are investments that mature within one year, and long-term marketable securities, with an aggregate fair value of $77,047, which consist of certain U.S. Treasury notes and corporate bonds that have maturities of more than one year but not more than three years.

Accrued Expenses and Other Long

Accrued Expenses and Other Long-Term Liabilities	3 Months Ended
	Dec. 31, 2017
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 December 31, 2017 and September 30, 2017: December 31, September 2017 2017 (in thousands) Accrued expenses: Accrued preclinical and clinical expenses $ 2,057 $ 3,156 Accrued vendor manufacturing 1,526 1,130 Accrued payroll and related expenses 1,186 2,829 Accrued professional fees 523 456 Accrued other 405 399 $ 5,697 $ 7,970 Other long-term liabilities: Uncertain tax positions $ 1,188 $ 1,175 Accrued rent expense 654 676 Capital lease obligation 358 379 Asset retirement obligation 190 180 $ 2,390 $ 2,410

Ongoing Collaboration Agreement

Ongoing Collaboration Agreements	3 Months Ended
	Dec. 31, 2017
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Ongoing Collaboration Agreements	6. Ongoing Collaboration Agreements 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 $525,000 through December 31, 2017. Since the Company completed all 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 also receiving annually tiered royalties per Company protease product ranging from the low double digits up to twenty percent, or on a blended basis from the low double digits up to the high teens, on the portion of AbbVie’s calendar year net sales of each HCV regimen that is allocated to the protease inhibitor 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. During the three months ended December 31, 2017, the Company earned and recognized milestone revenue of $15,000 upon AbbVie’s achievement of commercialization regulatory approval in Japan for MAVIRET™

Warrants to Purchase Series 1 N

Warrants to Purchase Series 1 Nonconvertible Preferred Stock and Series 1 Nonconvertible Preferred Stock	3 Months Ended
	Dec. 31, 2017
Debt Disclosure [Abstract]
Warrants to Purchase Series 1 Nonconvertible Preferred Stock and Series 1 Nonconvertible Preferred Stock	7. Warrants to Purchase Series 1 Nonconvertible Preferred Stock and Series 1 Nonconvertible Preferred Stock In October and November 2010, the Company issued warrants to purchase up to a total of 2,000 shares of Series 1 nonconvertible preferred stock. As these warrants were financial instruments that might have required the Company to transfer assets, these instruments are classified as liabilities. The following table summarizes the activity of the warrants to purchase Series 1 nonconvertible preferred stock: Outstanding Warrants Weighted Average Exercise Price (in thousands, except per share data) Outstanding as of September 30, 2017 1,030 $ 0.01 Exercised (978 ) $ 0.01 Expired (52 ) $ 0.01 Outstanding as of December 31, 2017 — $ 0.01 As of December 31, 2017, 1,931 shares of Series 1 nonconvertible preferred stock were issued and outstanding. As this preferred stock may require the Company to transfer a fixed amount of assets, these shares are classified as liabilities.

Stock-Based Awards

Stock-Based Awards	3 Months Ended
	Dec. 31, 2017
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Stock-Based Awards	8. Stock-Based Awards The Company has granted stock-based awards, including stock options, restricted stock units, and performance share units, under its existing 2012 Equity Incentive Plan (the “2012 Plan”). The Company also has outstanding stock-based awards under its 1995 Equity Incentive Plan (the “1995 Plan”), but is no longer granting awards under this plan. The following table summarizes stock option activity, including performance-based options, for the year-to-date period ending December 31, 2017: Shares Issuable Under Options (in thousands) Weighted Average Exercise Price Weighted Average Remaining Contractual Term (in years) Aggregate Intrinsic Value (in thousands) Outstanding as of September 30, 2017 2,298 $ 30.36 7.4 $ 37,821 Granted 466 $ 48.55 Exercised (29 ) $ 14.80 Forfeited (13 ) $ 39.45 Outstanding as of December 31, 2017 2,722 $ 33.60 7.7 $ 68,272 Options exercisable as of December 31, 2017 1,444 $ 29.19 6.6 $ 42,597 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 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 200% of the target number. 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, 2017 70 $ 34.51 70 $ 43.07 Granted — $ — — $ — Vested — $ — — $ — Cancelled — $ — — $ — Unvested at December 31, 2017 70 $ 34.51 70 $ 43.07 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 of these awards is determined based on the intrinsic value of the stock on the date of grant and will be 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 December 31, 2017: Restricted Stock Units Weighted Average Grant Date Fair Value (in thousands, except per share data) Unvested at September 30, 2017 110 $ 30.00 Granted — $ — Vested — $ — Cancelled — $ — Unvested at December 31, 2017 110 $ 30.00 Stock-Based Compensation Expense During the three months ended December 31, 2017 and 2016, the Company recognized the following stock-based compensation expense: Three Months ended December 31, 2017 2016 (in thousands) Research and development $ 1,471 $ 964 General and administrative 2,649 2,303 $ 4,120 $ 3,267 Three Months ended December 31, 2017 2016 (in thousands) Stock options $ 2,948 $ 2,346 Performance stock units 606 624 rTSRUs 362 203 Restricted stock units 204 94 $ 4,120 $ 3,267 During the three months ended December 31, 2017 and 2016, the Company recognized stock-based compensation expense for PSUs and performance-based options upon achievement of performance-based targets that occurred during their respective periods. As discussed in Note 2, the Company adopted ASU 2016-09 during the three months ended December 31, 2017. ASU 2016-09 intends to simplify several aspects of accounting for share-based payment transactions, including the income tax consequences, classification of awards as either equity or liabilities, a choice to recognize gross stock compensation expense with actual forfeitures recognized as they occur, as well as certain classifications on the statement of cash flows. As a result of the adoption, the Company changed its forfeiture rate policy to recognize forfeitures as they occur. Upon adoption, the cumulative impact of this change in policy on retained earnings and deferred tax assets in the consolidated balance sheet was not material. In addition, the consolidated statements of cash flows will present excess tax benefits, if any, as part of cash flows from operating activities. The Company elected to adopt this change on a prospective basis and, therefore, excess tax benefits from prior periods in the statement of cash flow were not retroactively restated. The adoption of the standard is also expected to create variability in the consolidated statements of operations in years in which the Company is expected to have taxable income, as the tax consequences of settled share-based payments will be recognized in income tax expense when share-based payment awards are settled . As of December 31, 2017, the Company had an aggregate of $32,132 of unrecognized stock-based compensation cost, which is expected to be recognized over a weighted average period of 2.7 years.

Net Income (Loss) Per Share

Net Income (Loss) Per Share	3 Months Ended
	Dec. 31, 2017
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 three months ended December 31, 2017 and 2016 (in thousands, except per share data): Three Months Ended December 31, 2017 2016 (in thousands, except per share data) Basic net income (loss) per share: Numerator: Net income (loss) $ 11,693 $ (4,980 ) Denominator: Weighted average common shares outstanding—basic 19,130 19,038 Net income (loss) per share common share—basic $ 0.61 $ (0.26 ) Diluted net income (loss) per share: Numerator: Net income (loss) $ 11,693 $ (4,980 ) Denominator: Weighted average common shares outstanding—basic 19,130 19,038 Dilutive effect of common stock equivalents 788 — Weighted average common shares outstanding—diluted 19,918 19,038 Net income (loss) per share common share—diluted $ 0.59 $ (0.26 ) Anti-dilutive common stock equivalents excluded from above 842 2,575 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 was in a net loss position since the impact of such common stock equivalents would have been anti-dilutive.

Income Taxes

Income Taxes	3 Months Ended
	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Income Taxes	10. Income Taxes For the three months ended December 31, 2017 and 2016, the Company recorded an income tax (expense) benefit of $(3,644) and $1,542, respectively, which was attributable to the Company’s domestic operations. During the three months ended December 31, 2017, income tax expense included a revaluation adjustment against deferred tax assets of $(3,859) due to a decrease in the federal corporate income tax rate as enacted under the U.S. Tax Cuts and Jobs Act (the “Tax Act”). The Company also recorded an income tax benefit of $215 during the three months ended December 31, 2017, primarily related to excess tax benefits for stock option activity which is now recorded in income tax expense (benefit) due to the adoption of ASU 2016-09 during the three months ended December 31, 2017. Estimates used to prepare our income tax expense are based on the Company’s initial analysis of . Given the complexity of the act, anticipated guidance from the U. S. Treasury regarding implementation of the act, and potential for additional guidance from the SEC and the Financial Accounting Standards Board related to the act, these estimates may be adjusted during fiscal 2018 to reflect any such guidance provided. During 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 statute from 2013 to the present. Earlier years may be examined to the extent that tax credit or net operating loss carryforwards are used in future periods. The Company is currently under examination by the Internal Revenue Service for the year ending September 30, 2016. No adjustments have been proposed to date. The Company has not received notice of examination by any other jurisdictions for any other tax year open under statute. The Company had an unrecognized tax benefit of $1,188 and $1,175 as of December 31, 2017 and September 30, 2017, 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.

Commitments and Contingencies

Commitments and Contingencies	3 Months Ended
	Dec. 31, 2017
Commitments And Contingencies Disclosure [Abstract]
Commitments and Contingencies	11. Commitments and Contingencies Leases The Company has an office and laboratory lease that expires in September 2022. Payment escalation as specified in the lease agreement is accrued such that rent expense is recognized on a straight-line basis over the term of occupancy. The Company recorded rent expense of $506 for both the three months ended December 31, 2017 and 2016. In connection with the lease, the Company has outstanding a $608 letter of credit, collateralized by a money market account. As of December 31, 2017 and September 30, 2017, the Company classified the $608 related to the letter of credit as restricted cash. Additionally, the lease, as amended, included a $598 tenant improvement allowance from the landlord, which is accounted for as a capital lease obligation. Litigation and Contingencies Related to Use of Intellectual Property From time to time, the Company may become subject to legal proceedings, claims and litigation arising in the ordinary course of business. The Company currently is not a party to any threatened or pending litigation. However, third parties might allege that the Company or its collaborators are infringing their patent rights or that the Company is otherwise violating their intellectual property rights. Such third parties may resort to litigation against the Company or its collaborators, which the Company has agreed to indemnify. With respect to some of these patents, the Company expects that it could 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 December 31, 2017.

Summary of Significant Accoun19

Summary of Significant Accounting Policies (Policies)	3 Months Ended
	Dec. 31, 2017
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 of separate units of accounting and best estimate of selling price of those units of accounting within its revenue arrangements; valuation of stock-based awards; and the accounting for income taxes, including uncertain tax positions and the valuation of net deferred tax assets. .
Recently Issued Accounting Pronouncements	Recently Issued Accounting Pronouncements In March 2016, the FASB issued ASU No. 2016-09, Improvements to Employee Share-Based Payment Accounting (“ASU 2016-09”), which intends to simplify several aspects of accounting for share-based payment transactions, including the income tax consequences, classification of awards as either equity or liabilities, a choice to recognize gross stock compensation expense with actual forfeitures recognized as they occur, as well as certain classifications on the statement of cash flows. This amendment is effective for the Company in the fiscal year beginning October 1, 2017. As a result of the adoption this quarter, the Company changed its forfeiture rate policy to recognize forfeitures as they occur. Upon adoption, the cumulative impact of this change in policy on retained earnings and deferred tax assets in the consolidated balance sheet was not material. In addition, the consolidated statements of cash flows will present excess tax benefits, if any, as part of cash flows from operating activities. The Company elected to adopt this change on a prospective basis and, therefore, excess tax benefits from prior periods in the statement of cash flow were not restated. The adoption of the standard is also expected to create variability in the consolidated statements of operations in years in which the Company is expected to have taxable income, as the tax consequences of settled share-based payments will be recognized in income tax expense when share-based payment awards are settled. In May 2014, the FASB issued ASU No. 2014-09, Revenue from Contracts with Customers (Topic 606) (“ASU 2014-09”) which supersedes all existing revenue recognition requirements, including most industry-specific guidance. The new standard requires a company to recognize revenue when it transfers goods or services to customers in an amount that reflects the consideration that the company expects to receive for those goods or services. The FASB has continued to issue accounting standards updates to clarify and provide implementation guidance related to Revenue from Contracts with Customers, including ASU 2016-08 , Revenue from Contract with Customers: Principal versus Agent Considerations , ASU 2016-10, Revenue from Contracts with Customers: Identifying Performance Obligations and Licensing , and ASU 2016-12, Revenue from Contracts with Customers: Narrow-Scope Improvements and Practical Expedients. These amendments address a number of areas, including an entity’s identification of its performance obligations in a contract, collectibility, non-cash consideration, presentation of sales tax and an entity’s evaluation of the nature of its promise to grant a license of intellectual property and whether or not that revenue is recognized over time or at a point in time. The new guidance must be adopted using either a modified retrospective approach or a full retrospective approach for all periods presented. Under the modified retrospective method, the cumulative effect of applying the new standard would be recognized at the adoption date in retained earnings on the consolidated balance sheet. Under the full retrospective approach, the new standard would be applied to each prior reporting period presented. These new standards will be effective for the Company beginning October 1, 2018. Currently, the Company has only one revenue-generating contract – the AbbVie Agreement. The Company has completed its substantial performance obligations under the contract and is eligible to earn annually tiered per-product royalties on the portion of AbbVie’s net sales of HCV regimens allocable to the protease inhibitor in the regimen. The Company is in process of determining the method of adoption but under either method, the impact of adoption is not expected to have a material impact on the Company’s consolidated financial statements as presently, the AbbVie Agreement is the only revenue-generating arrangement outstanding, and all performance obligations under the agreement have been achieved. In November 2016, the FASB issued ASU No. 2016-18, Statement of Cash Flows (Topic 230): Restricted Cash (“ASU 2016-18”) that changes the presentation of restricted cash and cash equivalents on the statement of cash flows. Restricted cash and restricted cash equivalents will be included with cash and cash equivalents when reconciling the beginning-of-period and end-of-period total amounts shown on the statement of cash flows. This amendment is effective for the Company in the fiscal year beginning October 1, 2018, but early adoption is permissible. Upon adoption, the Company will adjust the presentation of the statement of cash flows to include restricted cash related to an outstanding letter of credit collateralized by a money market fund of $608 so that it is included in the beginning balance of cash and cash equivalents. In May 2017, the FASB issued ASU No. 2017-09, Compensation—Stock Compensation (Topic 718) (“ASU 2017-09”) which This amendment is effective for the Company in the fiscal year beginning October 1, 2018, but early adoption is permissible. In February 2016, the FASB issued ASU No. 2016-02, Leases (“ASU 2016-02”), which will replace the existing guidance in ASC 840, “Leases.” The updated standard aims to increase transparency and comparability among organizations by requiring lessees to recognize leased assets and leased liabilities on the consolidated balance sheets and requiring disclosure of key information about leasing arrangements. This amendment is effective for the Company in the fiscal year beginning October 1, 2019, but early adoption is permissible. The Company is currently evaluating the potential impact that ASU 2016-02 may have on its financial position and results of operations. In March 2017, the FASB issued ASU No. 2017-08, Receivables—Nonrefundable Fees and Other Costs (Subtopic 310-20): Premium Amortization on Purchased Callable Debt Securities (“ASU 2017-08”) which requires companies to amend the amortization period for premiums on debt securities with explicit call features to be the earliest call date rather than through the contractual life of the debt instrument. This amendment aims to more closely align the recognition of interest income with the manner in which market participants price such instruments. This amendment is effective for the Company in the fiscal year beginning October 1, 2019, but early adoption is permissible. The Company is currently evaluating the potential impact that ASU 2017-08 may have on its financial position and results of operations. In June 2016, the FASB issued ASU No. 2016-13, Financial Instruments—Credit Losses (“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. This amendment is effective for the Company in the fiscal year beginning October 1, 2020. The Company is currently evaluating the potential impact that ASU 2016-13 may have on its financial position and results of operations. 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 Asset20

Fair Value of Financial Assets and Liabilities (Tables)	3 Months Ended
	Dec. 31, 2017
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 December 31, 2017 and September 30, 2017 and indicate the fair value hierarchy of the valuation inputs utilized to determine such fair value: Fair Value Measurements at December 31, 2017 Using: Level 1 Level 2 Level 3 Total (in thousands) Assets: Cash equivalents: Money market funds $ 36,702 $ — $ — $ 36,702 U.S. Treasury notes — 5,990 — 5,990 Commercial paper — 8,984 — 8,984 Marketable securities: U.S. Treasury notes 51,698 — — 51,698 Corporate bonds — 154,286 — 154,286 Commercial paper — 23,452 — 23,452 $ 88,400 $ 192,712 $ — $ 281,112 Liabilities: Warrant liability $ — $ — $ — $ — Series 1 nonconvertible preferred stock — — 1,528 1,528 $ — $ — $ 1,528 $ 1,528 Fair Value Measurements at September 30, 2017 Using: Level 1 Level 2 Level 3 Total (in thousands) Assets: Cash equivalents: Money market funds $ 19,863 $ — $ — $ 19,863 Commercial paper — 29,756 — 29,756 Corporate bonds — 3,000 — 3,000 Marketable securities: U.S. Treasury notes 60,843 — — 60,843 Corporate bonds — 150,731 — 150,731 Commercial paper — 12,458 — 12,458 U.S. Agency bonds — 4,000 — 4,000 $ 80,706 $ 199,945 $ — $ 280,651 Liabilities: Warrant liability $ — $ — $ 807 $ 807 Series 1 nonconvertible preferred stock — — 762 762 $ — $ — $ 1,569 $ 1,569
Fair Value Measurements of the Company's Outstanding Warrant Liability and Series 1 Nonconvertible Preferred Stock	The recurring Level 3 fair value measurements of the Company’s outstanding warrant liability and Series 1 nonconvertible preferred stock using probability-weighted discounted cash flow include the following significant unobservable inputs: Range (Weighted Average) December 31, September 30, Unobservable Input 2017 2017 Warrant liability and Series 1 nonconvertible preferred stock Probabilities of payout 0%-65% 0%-65% Discount rate 5.25% 5.25%
Rollforward of Aggregate Fair Values of Warrants and Outstanding Series 1 Nonconvertible Preferred Stock	The following table provides a rollforward of the aggregate fair values of the Company’s warrants for the purchase of Series 1 nonconvertible preferred stock and the outstanding Series 1 nonconvertible preferred stock for which fair value is determined by Level 3 inputs: Warrant Liability Series 1 Nonconvertible Preferred Stock Balance, September 30, 2017 $ 807 $ 762 Warrants exercised (766 ) 766 Warrants expired (41 ) — Balance, December 31, 2017 $ — $ 1,528

Marketable Securities (Tables)

Marketable Securities (Tables)	3 Months Ended
	Dec. 31, 2017
Investments Debt And Equity Securities [Abstract]
Fair Value of Available-for-Sale Marketable Securities by Type of Security	As of December 31, 2017 and September 30, 2017, the fair value of available-for-sale marketable securities, by type of security, was as follows: December 31, 2017 Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value (in thousands) Corporate bonds $ 154,778 $ — $ (492 ) $ 154,286 U.S. Treasury notes 51,838 — (140 ) 51,698 Commercial paper 23,452 — — 23,452 $ 230,068 $ — $ (632 ) $ 229,436 September 30, 2017 Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value (in thousands) Corporate bonds $ 150,841 $ 9 $ (119 ) $ 150,731 U.S. Treasury notes 60,908 — (65 ) 60,843 Commercial paper 12,458 — — 12,458 U.S. Agency bonds 4,004 — (4 ) 4,000 $ 228,211 $ 9 $ (188 ) $ 228,032

Accrued Expenses and Other Lo22

Accrued Expenses and Other Long-Term Liabilities (Tables)	3 Months Ended
	Dec. 31, 2017
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 December 31, 2017 and September 30, 2017: December 31, September 2017 2017 (in thousands) Accrued expenses: Accrued preclinical and clinical expenses $ 2,057 $ 3,156 Accrued vendor manufacturing 1,526 1,130 Accrued payroll and related expenses 1,186 2,829 Accrued professional fees 523 456 Accrued other 405 399 $ 5,697 $ 7,970 Other long-term liabilities: Uncertain tax positions $ 1,188 $ 1,175 Accrued rent expense 654 676 Capital lease obligation 358 379 Asset retirement obligation 190 180 $ 2,390 $ 2,410

Warrants to Purchase Series 123

Warrants to Purchase Series 1 Nonconvertible Preferred Stock and Series 1 Nonconvertible Preferred Stock (Tables)	3 Months Ended
	Dec. 31, 2017
Debt Disclosure [Abstract]
Summary of Activity of the Warrants to Purchase Series 1 Nonconvertible Preferred Stock	The following table summarizes the activity of the warrants to purchase Series 1 nonconvertible preferred stock: Outstanding Warrants Weighted Average Exercise Price (in thousands, except per share data) Outstanding as of September 30, 2017 1,030 $ 0.01 Exercised (978 ) $ 0.01 Expired (52 ) $ 0.01 Outstanding as of December 31, 2017 — $ 0.01

Stock-Based Awards (Tables)

Stock-Based Awards (Tables)	3 Months Ended
	Dec. 31, 2017
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 December 31, 2017: Shares Issuable Under Options (in thousands) Weighted Average Exercise Price Weighted Average Remaining Contractual Term (in years) Aggregate Intrinsic Value (in thousands) Outstanding as of September 30, 2017 2,298 $ 30.36 7.4 $ 37,821 Granted 466 $ 48.55 Exercised (29 ) $ 14.80 Forfeited (13 ) $ 39.45 Outstanding as of December 31, 2017 2,722 $ 33.60 7.7 $ 68,272 Options exercisable as of December 31, 2017 1,444 $ 29.19 6.6 $ 42,597
Summary of Restricted Stock Unit Activity	The following table summarizes the restricted stock unit activity for the year-to-date period ending December 31, 2017: Restricted Stock Units Weighted Average Grant Date Fair Value (in thousands, except per share data) Unvested at September 30, 2017 110 $ 30.00 Granted — $ — Vested — $ — Cancelled — $ — Unvested at December 31, 2017 110 $ 30.00
Stock-Based Compensation Expense	During the three months ended December 31, 2017 and 2016, the Company recognized the following stock-based compensation expense: Three Months ended December 31, 2017 2016 (in thousands) Research and development $ 1,471 $ 964 General and administrative 2,649 2,303 $ 4,120 $ 3,267 Three Months ended December 31, 2017 2016 (in thousands) Stock options $ 2,948 $ 2,346 Performance stock units 606 624 rTSRUs 362 203 Restricted stock units 204 94 $ 4,120 $ 3,267
Performance Share Units and Relative Total Stockholder Return Units [Member]
Summary of PSU and rTSRU Activity	The following table summarizes PSU and rTSRU activity for the year-to-date period ending December 31, 2017: 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, 2017 70 $ 34.51 70 $ 43.07 Granted — $ — — $ — Vested — $ — — $ — Cancelled — $ — — $ — Unvested at December 31, 2017 70 $ 34.51 70 $ 43.07

Net Income (Loss) Per Share (Ta

Net Income (Loss) Per Share (Tables)	3 Months Ended
	Dec. 31, 2017
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 three months ended December 31, 2017 and 2016 (in thousands, except per share data): Three Months Ended December 31, 2017 2016 (in thousands, except per share data) Basic net income (loss) per share: Numerator: Net income (loss) $ 11,693 $ (4,980 ) Denominator: Weighted average common shares outstanding—basic 19,130 19,038 Net income (loss) per share common share—basic $ 0.61 $ (0.26 ) Diluted net income (loss) per share: Numerator: Net income (loss) $ 11,693 $ (4,980 ) Denominator: Weighted average common shares outstanding—basic 19,130 19,038 Dilutive effect of common stock equivalents 788 — Weighted average common shares outstanding—diluted 19,918 19,038 Net income (loss) per share common share—diluted $ 0.59 $ (0.26 ) Anti-dilutive common stock equivalents excluded from above 842 2,575

Summary of Significant Accoun26

Summary of Significant Accounting Policies - Additional Information (Detail) $ in Thousands	Dec. 31, 2017USD ($)Contract	Sep. 30, 2017USD ($)
Summary Of Accounting And Financial Policies [Line Items]
Number of revenue-generating contract | Contract	1
Outstanding letter of credit	$ 608	$ 608
ASU 2016-18 [Member]
Summary Of Accounting And Financial Policies [Line Items]
Outstanding letter of credit	$ 608

Fair Value of Financial Asset27

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	Dec. 31, 2017	Sep. 30, 2017
Assets:
Available for sale securities, fair value	$ 229,436	$ 228,032
Assets, Fair Value Disclosure, Total	281,112	280,651
Liabilities:
Liabilities, Fair Value Disclosure, Total	1,528	1,569
Warrant Liability [Member]
Liabilities:
Liabilities		807
Series 1 Nonconvertible Preferred Stock [Member]
Liabilities:
Liabilities	1,528	762
Level 1 [Member]
Assets:
Assets, Fair Value Disclosure, Total	88,400	80,706
Level 2 [Member]
Assets:
Assets, Fair Value Disclosure, Total	192,712	199,945
Level 3 [Member]
Liabilities:
Liabilities, Fair Value Disclosure, Total	1,528	1,569
Level 3 [Member] | Warrant Liability [Member]
Liabilities:
Liabilities		807
Level 3 [Member] | Series 1 Nonconvertible Preferred Stock [Member]
Liabilities:
Liabilities	1,528	762
U.S. Treasury Notes [Member]
Assets:
Cash equivalents	5,990
Available for sale securities, fair value	51,698	60,843
U.S. Treasury Notes [Member] | Level 1 [Member]
Assets:
Available for sale securities, fair value	51,698	60,843
U.S. Treasury Notes [Member] | Level 2 [Member]
Assets:
Cash equivalents	5,990
Money Market Funds [Member]
Assets:
Cash equivalents	36,702	19,863
Money Market Funds [Member] | Level 1 [Member]
Assets:
Cash equivalents	36,702	19,863
Corporate Bonds [Member]
Assets:
Cash equivalents		3,000
Available for sale securities, fair value	154,286	150,731
Corporate Bonds [Member] | Level 2 [Member]
Assets:
Cash equivalents		3,000
Available for sale securities, fair value	154,286	150,731
Commercial Paper [Member]
Assets:
Cash equivalents	8,984	29,756
Available for sale securities, fair value	23,452	12,458
Commercial Paper [Member] | Level 2 [Member]
Assets:
Cash equivalents	8,984	29,756
Available for sale securities, fair value	$ 23,452	12,458
U.S. Agency Bonds [Member]
Assets:
Available for sale securities, fair value		4,000
U.S. Agency Bonds [Member] | Level 2 [Member]
Assets:
Available for sale securities, fair value		$ 4,000

Fair Value of Financial Asset28

Fair Value of Financial Assets and Liabilities - Additional Information (Detail) - USD ($)	3 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Fair Value Disclosures [Abstract]
Transfers between Level 1, Level 2 and Level 3	$ 0	$ 0
Warrant expiration date	Oct. 4, 2017
Warrants outstanding	0

Fair Value of Financial Asset29

Fair Value of Financial Assets and Liabilities - Fair Value Measurements of the Company's Outstanding Warrant Liability and Series 1 Nonconvertible Preferred Stock (Detail) - Warrant Liability [Member] - Series 1 Nonconvertible Preferred Stock [Member]	3 Months Ended	12 Months Ended
	Dec. 31, 2017	Sep. 30, 2016
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Discount rate	5.25%	5.25%
Minimum [Member]
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Probabilities of payout	0.00%	0.00%
Maximum [Member]
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Probabilities of payout	65.00%	65.00%

Fair Value of Financial Asset30

Fair Value of Financial Assets and Liabilities - Rollforward of Aggregate Fair Values of Warrants (Detail) $ in Thousands	3 Months Ended
	Dec. 31, 2017USD ($)
Series 1 Nonconvertible Preferred Stock [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning Balance	$ 762
Warrants exercised	766
Ending Balance	1,528
Warrant Liability [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning Balance	807
Warrants exercised	(766)
Warrants expired	$ (41)

Marketable Securities - Fair Va

Marketable Securities - Fair Value of Available-for-Sale Marketable Securities by Type of Security (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Sep. 30, 2017
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 230,068	$ 228,211
Gross Unrealized Gains		9
Gross Unrealized Losses	(632)	(188)
Fair Value	229,436	228,032
Corporate Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	154,778	150,841
Gross Unrealized Gains		9
Gross Unrealized Losses	(492)	(119)
Fair Value	154,286	150,731
U.S. Treasury Notes [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	51,838	60,908
Gross Unrealized Losses	(140)	(65)
Fair Value	51,698	60,843
Commercial Paper [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	23,452	12,458
Fair Value	$ 23,452	12,458
U.S. Agency Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		4,004
Gross Unrealized Losses		(4)
Fair Value		$ 4,000

Marketable Securities - Additio

Marketable Securities - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017
Schedule of Available-for-sale Securities [Line Items]
Marketable securities maturing not less than three years, aggregate fair value	$ 77,047	$ 70,038	$ 77,047
Short Term Marketable Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Maturity period of the marketable securities	Within one year
Long Term Marketable Securities [Member] | U.S. Treasury Notes [Member]
Schedule of Available-for-sale Securities [Line Items]
Maturity period of the marketable securities	more than one year but not more than three years
Long Term Marketable Securities [Member] | Corporate Bond Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Maturity period of the marketable securities	more than one year but not more than three years

Accrued Expenses and Other Lo33

Accrued Expenses and Other Long-Term Liabilities - Accrued Expenses and Other Current Liabilities as well as Other Long-Term Liabilities (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Sep. 30, 2017
Accrued expenses:
Accrued preclinical and clinical expenses	$ 2,057	$ 3,156
Accrued vendor manufacturing	1,526	1,130
Accrued payroll and related expenses	1,186	2,829
Accrued professional fees	523	456
Accrued other	405	399
Accrued expenses	5,697	7,970
Other long-term liabilities:
Uncertain tax positions	1,188	1,175
Accrued rent expense	654	676
Capital lease obligation	358	379
Asset retirement obligation	190	180
Other long-term liabilities	$ 2,390	$ 2,410

Ongoing Collaboration Agreeme34

Ongoing Collaboration Agreements - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended	134 Months Ended
	Dec. 31, 2017	Dec. 31, 2017
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Milestone revenue recognized	$ 15,000
AbbVie [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaboration agreement tiered royalty description	From the low double digits up to twenty percent, or on a blended basis from the low double digits up to the high teens, on the portion of AbbVie’s calendar year net sales
AbbVie [Member] | Milestone Payments [Member] | Paritaprevir 3-DAA Regimen [Member] | JAPAN
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Milestone revenue recognized	$ 15,000
Milestone Payments and Royalties [Member] | AbbVie [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Proceed received to fund research activities and preferred stock financing		$ 525,000

Warrants to Purchase Series 135

Warrants to Purchase Series 1 Nonconvertible Preferred Stock and Series 1 Nonconvertible Preferred Stock - Additional Information (Detail) - Series 1 Nonconvertible Preferred Stock [Member] - shares shares in Thousands	Dec. 31, 2017	Nov. 30, 2010
Class of Warrant or Right [Line Items]
Number of shares issuable upon exercise of the warrants		2,000
Preferred stock, shares issued	1,931
Preferred stock, shares outstanding	1,931

Warrants to Purchase Series 136

Warrants to Purchase Series 1 Nonconvertible Preferred Stock and Series 1 Nonconvertible Preferred Stock - Summary of Activity of the Warrants to Purchase Series 1 Nonconvertible Preferred Stock (Detail) shares in Thousands	3 Months Ended
	Dec. 31, 2017$ / sharesshares
Warrants And Rights Note Disclosure [Abstract]
Beginning Balance | shares	1,030
Exercised | shares	(978)
Expired | shares	(52)
Weighted Average Exercise Price Outstanding, Beginning Balance	$ 0.01
Weighted Average Exercise Price Outstanding, Exercised	0.01
Weighted Average Exercise Price Outstanding, Expired	0.01
Weighted Average Exercise Price Outstanding, Ending Balance	$ 0.01

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	3 Months Ended	12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017
Options
Outstanding as of beginning of period	2,298
Granted	466
Exercised	(29)
Forfeited	(13)
Outstanding as of end of period	2,722	2,298
Options exercisable as of end of period	1,444
Weighted Average Exercise Price
Outstanding	$ 30.36
Granted	48.55
Exercised	14.80
Forfeited	39.45
Outstanding	33.60	$ 30.36
Options exercisable as of end of period	$ 29.19
Weighted Average Remaining Contractual Term
Outstanding as of end of period	7 years 8 months 12 days	7 years 4 months 24 days
Options exercisable as of end of period	6 years 7 months 6 days
Aggregate Intrinsic Value
Aggregate Intrinsic Value	$ 68,272	$ 37,821
Options exercisable as of end of period	$ 42,597

Stock-Based Awards - Additional

Stock-Based Awards - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Aggregate of unrecognized stock-based compensation cost	$ 32,132
Weighted average recognition period	2 years 8 months 13 days
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	200.00%

Stock-Based Awards - Summary 39

Stock-Based Awards - Summary of PSU and rTSRU Activity (Detail) shares in Thousands	Dec. 31, 2017$ / sharesshares
PSUs [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unvested, beginning balance | shares	70
Unvested, ending balance | shares	70
Weighted Average Grant Date Fair Value, Unvested beginning balance | $ / shares	$ 34.51
Weighted Average Grant Date Fair Value, Unvested ending balance | $ / shares	$ 34.51
rTSRUs [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unvested, beginning balance | shares	70
Unvested, ending balance | shares	70
Weighted Average Grant Date Fair Value, Unvested beginning balance | $ / shares	$ 43.07
Weighted Average Grant Date Fair Value, Unvested ending balance | $ / shares	$ 43.07

Stock-Based Awards - Summary 40

Stock-Based Awards - Summary of Restricted Stock Unit Activity (Detail) - Restricted Stock Units [Member] shares in Thousands	Dec. 31, 2017$ / sharesshares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unvested, beginning balance | shares	110
Unvested, ending balance | shares	110
Weighted Average Grant Date Fair Value, Unvested beginning balance | $ / shares	$ 30
Weighted Average Grant Date Fair Value, Unvested ending balance | $ / shares	$ 30

Stock-Based Awards - Stock-Base

Stock-Based Awards - Stock-Based Compensation Expense (Detail) - USD ($) $ in Thousands	3 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	$ 4,120	$ 3,267
Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	2,948	2,346
Performance Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	606	624
rTSRUs [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	362	203
Restricted Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	204	94
Research and Development [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	1,471	964
General and Administrative [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	$ 2,649	$ 2,303

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
	Dec. 31, 2017	Dec. 31, 2016
Basic net income (loss) per share:
Net income (loss)	$ 11,693	$ (4,980)
Weighted average common shares outstanding—basic	19,130	19,038
Net income (loss) per share common share—basic	$ 0.61	$ (0.26)
Diluted net income (loss) per share:
Net income (loss)	$ 11,693	$ (4,980)
Weighted average common shares outstanding—basic	19,130	19,038
Dilutive effect of common stock equivalents	788
Weighted average common shares outstanding—diluted	19,918	19,038
Net income (loss) per share common share—diluted	$ 0.59	$ (0.26)
Anti-dilutive common stock equivalents excluded from above	842	2,575

Income Taxes - Additional Infor

Income Taxes - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Sep. 30, 2017
Income Tax [Line Items]
Income tax (expense) benefit	$ (3,644)	$ 1,542
Income tax expense as a result of U.S. Tax Cuts and Jobs Act	(3,859)
Unrecognized tax benefits	1,188		$ 1,175
ASU 2016-09 [Member]
Income Tax [Line Items]
Income tax (expense) benefit	$ 215

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Sep. 30, 2017
Commitments And Contingencies Disclosure [Abstract]
Office lease expiration period	Sep. 30, 2022
Rent expense	$ 506	$ 506
Outstanding letter of credit	608		$ 608
Restricted cash	608		$ 608
Tenant improvement allowance	$ 598