Enanta Pharmaceuticals (ENTA) 10-Q 9 Aug 17 2017 Q3 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	9 Months Ended
	Jun. 30, 2017	Aug. 01, 2017
Document And Entity Information [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Jun. 30, 2017
Document Fiscal Year Focus	2,017
Document Fiscal Period Focus	Q3
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		19,090,383

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Jun. 30, 2017	Sep. 30, 2016
Current assets:
Cash and cash equivalents	$ 22,263	$ 16,577
Short-term marketable securities	169,752	193,507
Accounts receivable	7,511	12,841
Prepaid expenses and other current assets	6,589	9,231
Total current assets	206,115	232,156
Property and equipment, net	8,070	8,004
Long-term marketable securities	43,321	32,119
Deferred tax assets	17,723	8,390
Restricted cash	608	608
Total assets	275,837	281,277
Current liabilities:
Accounts payable	5,488	3,377
Accrued expenses and other current liabilities	5,634	4,512
Total current liabilities	11,122	7,889
Warrant liability	1,291	1,251
Series 1 nonconvertible preferred stock	164	159
Other long-term liabilities	2,394	2,042
Total liabilities	14,971	11,341
Commitments and contingencies (Note 11)
Stockholders' equity:
Common stock; $0.01 par value per share, 100,000 shares authorized; 19,090 and 19,036 shares issued and outstanding at June 30, 2017 and September 30, 2016, respectively	191	190
Additional paid-in capital	251,964	242,081
Accumulated other comprehensive income (loss)	(137)	19
Retained earnings	8,848	27,646
Total stockholders' equity	260,866	269,936
Total liabilities and stockholders' equity	$ 275,837	$ 281,277

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - $ / shares	Jun. 30, 2017	Sep. 30, 2016
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	19,090,000	19,036,000
Common stock, shares outstanding	19,090,000	19,036,000

Consolidated Statements of Oper

Consolidated Statements of Operations - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Revenue
Royalties	$ 7,511	$ 13,978	$ 26,887	$ 44,851
Milestones				30,000
Other				576
Total revenue	7,511	13,978	26,887	75,427
Operating expenses:
Research and development	15,407	10,785	40,937	28,961
General and administrative	5,233	4,282	15,631	12,526
Total operating expenses	20,640	15,067	56,568	41,487
Income (loss) from operations	(13,129)	(1,089)	(29,681)	33,940
Other income (expense):
Interest income	628	474	1,749	1,238
Interest expense	(11)	(11)	(31)	(34)
Change in fair value of warrant liability and Series 1 nonconvertible preferred stock	(17)	(16)	(45)	44
Total other income (expense), net	600	447	1,673	1,248
Income (loss) before income taxes	(12,529)	(642)	(28,008)	35,188
Income tax (expense) benefit	4,103	(434)	9,210	(11,720)
Net income (loss)	$ (8,426)	$ (1,076)	$ (18,798)	$ 23,468
Net income (loss) per share:
Basic	$ (0.44)	$ (0.06)	$ (0.99)	$ 1.24
Diluted	$ (0.44)	$ (0.06)	$ (0.99)	$ 1.22
Weighted average shares outstanding:
Basic	19,081	18,983	19,055	18,893
Diluted	19,081	18,983	19,055	19,223

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Income (Loss) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Statement Of Income And Comprehensive Income [Abstract]
Net income (loss)	$ (8,426)	$ (1,076)	$ (18,798)	$ 23,468
Other comprehensive income (loss):
Net unrealized gains (losses) on marketable securities, net of tax of ($17), $185, ($93), $50	(29)	(84)	(156)	84
Total other comprehensive income (loss)	(29)	(84)	(156)	84
Comprehensive income (loss)	$ (8,455)	$ (1,160)	$ (18,954)	$ 23,552

Consolidated Statements of Com6

Consolidated Statements of Comprehensive Income (Loss) (Parenthetical) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Statement Of Income And Comprehensive Income [Abstract]
Net unrealized gains on marketable securities, tax	$ (17)	$ 185	$ (93)	$ 50

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Jun. 30, 2017	Jun. 30, 2016
Cash flows from operating activities
Net income (loss)	$ (18,798)	$ 23,468
Adjustments to reconcile net income (loss) to net cash provided by (used in) operating activities:
Stock-based compensation expense	9,861	6,844
Depreciation and amortization expense	1,573	1,206
Deferred income taxes	(9,240)	546
Income tax benefit from exercise of stock options		(1,749)
Premium on marketable securities	(840)	(130)
Amortization of premium on marketable securities	564	1,304
Change in fair value of warrant liability and Series 1 nonconvertible preferred stock	45	(44)
Change in operating assets and liabilities:
Accounts receivable	5,330	1,311
Unbilled receivables		433
Prepaid expenses and other current assets	2,584	67
Accounts payable	2,717	677
Accrued expenses	1,145	1,946
Income taxes payable		1,754
Other long-term liabilities	406	302
Net cash provided by (used in) operating activities	(4,653)	37,935
Cash flows from investing activities
Purchase of property and equipment	(2,272)	(4,323)
Purchase of marketable securities	(186,222)	(150,490)
Proceeds from maturities and sales of marketable securities	198,823	117,297
Net cash provided by (used in) investing activities	10,329	(37,516)
Cash flows from financing activities
Proceeds from exercise of stock options	266	945
Payments of capital lease obligations	(54)	(50)
Payments of withholding tax for share-based awards	(202)
Income tax benefit from exercise of stock options		1,749
Net cash provided by financing activities	10	2,644
Net increase in cash and cash equivalents	5,686	3,063
Cash and cash equivalents at beginning of period	16,577	21,726
Cash and cash equivalents at end of period	22,263	24,789
Supplemental disclosure of cash flow information:
Cash paid for income taxes	$ 1,027	$ 9,116

Nature of the Business and Basi

Nature of the Business and Basis of Presentation	9 Months Ended
	Jun. 30, 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 research and development-focused 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’s success to date has been built on protease inhibitors discovered for the treatment of hepatitis C virus, or (“HCV”), which are licensed to AbbVie Inc. (“ and included in its HCV treatment regimens. The Company’s research and development programs are currently focused primarily on the following disease areas 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, 2016 was derived from audited financial statements, but does not include all disclosures required by accounting principles generally accepted in the United States of America (“GAAP”). The accompanying unaudited consolidated financial statements as of June 30, 2017 and for the nine months ended June 30, 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, 2016. In the opinion of management, all adjustments, consisting of normal recurring adjustments necessary for a fair statement of the Company’s financial position as of June 30, 2017 and results of operations for the three and nine months ended June 30, 2017 and 2016 and cash flows for the nine months ended June 30, 2017 and 2016, have been made. The results of operations for the nine months ended June 30, 2017 are not necessarily indicative of the results of operations that may be expected for subsequent quarters or the year ending September 30, 2017. 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 share and per share amounts, are in thousands unless otherwise indicated.

Summary of Significant Accounti

Summary of Significant Accounting Policies	9 Months Ended
	Jun. 30, 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, 2016. There were no 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 warrants, Series 1 nonconvertible preferred stock and 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 August 2014, the Financial Accounting Standards Board (the “ Presentation of Financial Statements - Going Concern (Subtopic 205-40) 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 will be effective for the Company in the fiscal year beginning October 1, 2017. Once adopted, the Company expects to change its policy over forfeitures by recording forfeitures as they occur. The Company is currently evaluating the impact of this change to retained earnings in the consolidated balance sheets. In addition, the adoption of the standard is expected to create variability in the consolidated statements of operations going forward as the tax consequences of settled share-based payments will be recognized in income tax (expense) benefit 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. These new standards will be effective for the Company beginning October 1, 2018. The Company is currently evaluating the potential impact that Topic 606 may have on its financial position and results of operations. 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. The Company is currently evaluating the potential impact that ASU 2016-18 may have on its statement of cash flows. 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 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, 2019, but early adoption is permissible. The Company is currently evaluating the potential impact that ASU 2017-09 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	9 Months Ended
	Jun. 30, 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 June 30, 2017 and September 30, 2016 and indicate the fair value hierarchy of the valuation inputs utilized to determine such fair value: Fair Value Measurements at June 30, 2017 Using: Level 1 Level 2 Level 3 Total Assets: U.S. Treasury notes $ 63,897 $ — $ — $ 63,897 Cash equivalents 7,102 — — 7,102 Corporate bonds — 119,203 — 119,203 Commercial paper — 25,976 — 25,976 U.S. Agency bonds — 3,997 — 3,997 $ 70,999 $ 149,176 $ — $ 220,175 Liabilities: Warrant liability $ — $ — $ 1,291 $ 1,291 Series 1 nonconvertible preferred stock — — 164 164 $ — $ — $ 1,455 $ 1,455 Fair Value Measurements at September 30, 2016 Using: Level 1 Level 2 Level 3 Total Assets: U.S. Treasury notes $ 69,608 $ — $ — $ 69,608 Cash equivalents 15,295 — — 15,295 Corporate bonds — 76,073 — 76,073 Commercial paper — 49,900 — 49,900 U.S. Agency bonds — 30,045 — 30,045 $ 84,903 $ 156,018 $ — $ 240,921 Liabilities: Warrant liability $ — $ — $ 1,251 $ 1,251 Series 1 nonconvertible preferred stock — — 159 159 $ — $ — $ 1,410 $ 1,410 Cash equivalents consist primarily of money market funds and debt securities with less than a 90 day maturity period. During the nine months ended June 30, 2017 and 2016, there were no transfers between Level 1, Level 2 and Level 3. As of June 30, 2017 and September 30, 2016, the Company’s warrant liability was comprised of the value of warrants for the purchase of its Series 1 nonconvertible preferred stock. These warrants are financial instruments that may require a transfer of assets because of the liquidation features and are therefore recorded as liabilities and measured at fair value. The outstanding Series 1 nonconvertible preferred stock was 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 warrant liability and Series 1 nonconvertible preferred stock using probability-weighted discounted cash flow include the following significant unobservable inputs: Range (Weighted Average) June 30, September 30, Unobservable Input 2017 2016 Warrant liability and Series 1 nonconvertible preferred stock Probabilities of payout 0%-60% 0%-60% Periods in which payout is expected to occur 2018 2017-2018 Discount rate 5.25% 4.50% 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, 2016 $ 1,251 $ 159 Increase in fair value 40 5 Balance, June 30, 2017 $ 1,291 $ 164

Marketable Securities

Marketable Securities	9 Months Ended
	Jun. 30, 2017
Investments Debt And Equity Securities [Abstract]
Marketable Securities	4. Marketable Securities As of June 30, 2017 and September 30, 2016, the fair value of available-for-sale marketable securities, by type of security, was as follows: June 30, 2017 Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value Corporate bonds $ 119,298 $ 7 $ (102 ) $ 119,203 U.S. Treasury notes 64,010 — (113 ) 63,897 Commercial paper 25,976 — — 25,976 U.S. Agency bonds 4,008 — (11 ) 3,997 $ 213,292 $ 7 $ (226 ) $ 213,073 September 30, 2016 Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value Corporate bonds $ 76,077 $ 27 $ (31 ) $ 76,073 U.S. Treasury notes 69,579 38 (9 ) 69,608 Commercial paper 49,900 — — 49,900 U.S. Agency bonds 30,040 15 (10 ) 30,045 $ 225,596 $ 80 $ (50 ) $ 225,626 As of June 30, 2017, marketable securities consisted of short-term marketable securities, which are investments that mature within one year, and long-term marketable securities, 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 and an aggregate fair value of $43,321.

Accrued Expenses and Other Long

Accrued Expenses and Other Long-Term Liabilities	9 Months Ended
	Jun. 30, 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 June 30, 2017 and September 30, 2016: June 30, September 2017 2016 Accrued expenses: Accrued preclinical and clinical expenses $ 2,024 $ 899 Accrued payroll and related expenses 2,002 2,384 Accrued professional fees 639 393 Accrued vendor manufacturing 452 441 Capital lease obligation 75 73 Accrued other 442 322 $ 5,634 $ 4,512 Other long-term liabilities: Uncertain tax positions $ 1,109 $ 745 Accrued rent expense 711 696 Capital lease obligation 402 458 Asset retirement obligation 172 143 $ 2,394 $ 2,042

Ongoing Collaboration Agreement

Ongoing Collaboration Agreements	9 Months Ended
	Jun. 30, 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 (ABT-493), under which the Company has received license payments, proceeds from a sale of preferred stock, research funding payments, milestone payments and royalties totaling approximately $427,000 through June 30, 2017. Since the Company completed all its performance obligations under the AbbVie Agreement by the end of fiscal 2011, any milestone payments received since then have been and will be recognized as revenue when the milestones are achieved by AbbVie. As of June 30, 2017, the Company is eligible to receive additional milestone payments of up to a total of $80,000 upon AbbVie’s achievement of commercialization regulatory approval in the U.S. and other major world markets for its glecaprevir/pibrentasvir (“G/P”) combination regimen for HCV. 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 product start at zero for purposes of calculating the tiered royalties on a product-by-product basis. During the nine months ended June 30, 2016, the Company earned and recognized milestone revenue of $30,000 upon AbbVie’s achievement of commercialization regulatory approval of a paritaprevir-containing regimen in Japan in November 2015.

Warrants to Purchase Series 1 N

Warrants to Purchase Series 1 Nonconvertible Preferred Stock and Series 1 Nonconvertible Preferred Stock	9 Months Ended
	Jun. 30, 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 1,999,989 shares of Series 1 nonconvertible preferred stock, which expire on October 4, 2017. As these warrants and underlying Series 1 preferred stock are financial instruments that may require the Company to transfer assets, these instruments are classified as liabilities. The Company is required to remeasure the fair value of these instruments at each reporting date, with any adjustments recorded within other income (expense), net, in the consolidated statements of operations.

Stock-Based Awards

Stock-Based Awards	9 Months Ended
	Jun. 30, 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 and restricted stock 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 June 30, 2017: Shares Issuable Under Options Weighted Average Exercise Price Weighted Average Remaining Contractual Term in years Aggregate Intrinsic Value Outstanding as of September 30, 2016 1,895,456 $ 28.75 7.6 $ 7,369 Granted 559,019 30.04 Exercised (41,789 ) 6.36 Forfeited (132,655 ) 18.20 Outstanding as of June 30, 2017 2,280,031 $ 30.09 7.6 $ 17,347 Options vested and expected to vest as of June 30, 2017 2,264,139 $ 30.08 7.6 $ 9,358 Options exercisable as of June 30, 2017 1,259,717 $ 28.06 6.7 $ 12,257 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. Performance Share Units Weighted Average Grant Date Fair Value Relative Total Stockholder Return Units Weighted Average Grant Date Fair Value Unvested at September 30, 2016 48,525 $ 33.70 48,525 $ 31.74 Granted 44,500 $ 35.89 44,500 $ 46.11 Vested (18,820 ) $ 35.47 — $ — Cancelled (4,705 ) $ 35.47 (23,525 ) $ 25.44 Unvested at June 30, 2017 69,500 $ 34.51 69,500 $ 43.07 Restricted Stock Units During the nine months ended June 30, 2017, 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, net of estimated forfeitures, over the requisite service period. The following table summarizes the restricted stock unit activity for the year-to-date period ending June 30, 2017: Restricted Stock Units Weighted Average Grant Date Fair Value Unvested at September 30, 2016 — $ — Granted 112,460 $ 30.00 Vested — $ — Cancelled (2,104 ) $ 30.00 Unvested at June 30, 2017 110,356 $ 30.00 Stock-Based Compensation Expense During the three and nine months ended June 30, 2017 and 2016 the Company recognized the following stock-based compensation expense: Three Months ended Nine Months Ended June 30, June 30, 2017 2016 2017 2016 Research and development $ 990 $ 790 $ 2,998 $ 2,092 General and administrative 2,112 1,680 6,863 4,752 $ 3,102 $ 2,470 $ 9,861 $ 6,844 Three Months ended Nine Months Ended June 30, June 30, 2017 2016 2017 2016 Stock options $ 2,544 $ 2,270 $ 7,797 $ 6,354 Performance stock units — — 667 — rTSRUs 358 200 905 490 Restricted stock units 200 — 492 — $ 3,102 $ 2,470 $ 9,861 $ 6,844 During the nine months ended June 30, 2017, the Company recognized stock-based compensation expense for PSUs and performance-based options upon achievement of performance-based targets that occurred during the year-to-date period. As of June 30, 2017, the Company had an aggregate of $26,797 unrecognized stock-based compensation cost, which is expected to be recognized over a weighted average period of 2.3 years.

Net Income (Loss) Per Share

Net Income (Loss) Per Share	9 Months Ended
	Jun. 30, 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 nine months ended June 30, 2017 and 2016 (in thousands, except per share data): Three Months Ended Nine Months Ended June 30, June 30, 2017 2016 2017 2016 Basic net income (loss) per share: Numerator: Net income (loss) $ (8,426 ) $ (1,076 ) $ (18,798 ) $ 23,468 Denominator: Weighted average common shares outstanding—basic 19,081 18,983 19,055 18,893 Net income (loss) per share common share—basic $ (0.44 ) $ (0.06 ) $ (0.99 ) $ 1.24 Diluted net income (loss) per share: Numerator: Net income (loss) $ (8,426 ) $ (1,076 ) $ (18,798 ) $ 23,468 Denominator: Weighted average common shares outstanding—basic 19,081 18,983 19,055 18,893 Dilutive effect of common stock equivalents — — — 330 Weighted average common shares outstanding— diluted 19,081 18,983 19,055 19,223 Net income (loss) per share common share—diluted $ (0.44 ) $ (0.06 ) $ (0.99 ) $ 1.22 Anti-dilutive common stock equivalents excluded from above 2,244 1,620 1,832 1,250 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. As of June 30, 2017, the Company also excluded 139,000 of unvested stock awards from the calculation of diluted net income (loss) per common share as these awards contain performance or market conditions that would not have been achieved as of June 30, 2017 had the measurement period been as of that date.

Income Taxes

Income Taxes	9 Months Ended
	Jun. 30, 2017
Income Tax Disclosure [Abstract]
Income Taxes	10. Income Taxes For the three months ended June 30, 2017 and 2016, the Company recorded an income tax (expense) benefit of $4,103 and ($434), respectively, which was primarily attributable to the Company’s domestic operations. During the three months ended June 30, 2017, the Company’s income tax benefit was due to the Company’s pre-tax loss for the quarter. During the Company increased its estimate of its annual effective tax rate for fiscal 2016, which resulted in an income tax expense despite a pre-tax loss for the quarter. For the nine months ended June 30, 2017 and 2016, the Company recorded an income tax (expense) benefit of $9,210 and $(11,720) respectively. For the nine months ended June 30, 2017, the Company’s effective tax rate of 32.9% differs from the statutory rate of 35.0% primarily due to research and development tax credits which reduced the Company’s annual effective tax rate slightly below the statutory rate. For the nine months ended June 30, 2016, the Company’s effective tax rate of 33.3% differs from the statutory rate of 35.0% primarily d ue to the reinstatement of federal research and development tax credits which are included in the Company’s annual effective tax rate 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. There are currently no pending income tax examinations. 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 credits or net operating loss carryforwards are used in future periods. The Company had an unrecognized tax benefit of $1,109 and $745 as of June 30, 2017 and September 30, 2016, 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	9 Months Ended
	Jun. 30, 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 $1,519 for both the nine months ended June 30, 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 June 30, 2017 and September 30, 2016, 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. Intellectual Property Licenses The Company has a non-exclusive intellectual property license agreement with a third party, under which the Company is required to pay (1) annual maintenance fees for each year that the agreement remains in effect, commencing on the first anniversary of the agreement, in order to maintain the right to use the license, and (2) a one-time fee of in each circumstance in which the Company provides the licensed intellectual property to one of its collaborators with the prior consent of the licensor. 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, from services to be provided by the Company, or from intellectual property infringement claims made by third parties. In addition, the Company has entered into indemnification agreements with members of its board of directors and its executive officers that will require the Company, among other things, to indemnify them against certain liabilities that may arise by reason of their status or service as directors or officers. The maximum potential amount of future payments the Company could be required to make under these indemnification agreements is, in many cases, unlimited. To date, the Company has not incurred any material costs as a result of such indemnifications. In addition, the Company maintains officers and directors insurance coverage. The Company does not believe that the outcome of any claims under indemnification arrangements will have a material effect on its financial position, results of operations or cash flows, and it has not accrued any liabilities related to such obligations in its financial statements as of June 30, 2017.

Subsequent Events

Subsequent Events	9 Months Ended
	Jun. 30, 2017
Subsequent Events [Abstract]
Subsequent Events	12. Subsequent Events Under its Collaboration Agreement with AbbVie, the Company is eligible to receive milestone payments upon AbbVie’s achievement of commercialization regulatory approval milestones in the U.S. and other major world markets for any AbbVie therapies for HCV containing the Company’s protease inhibitors. After AbbVie received marketing authorization for its new MAVIRET MAVYRET

Summary of Significant Accoun20

Summary of Significant Accounting Policies (Policies)	9 Months Ended
	Jun. 30, 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 warrants, Series 1 nonconvertible preferred stock and 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 August 2014, the Financial Accounting Standards Board (the “ Presentation of Financial Statements - Going Concern (Subtopic 205-40) 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 will be effective for the Company in the fiscal year beginning October 1, 2017. Once adopted, the Company expects to change its policy over forfeitures by recording forfeitures as they occur. The Company is currently evaluating the impact of this change to retained earnings in the consolidated balance sheets. In addition, the adoption of the standard is expected to create variability in the consolidated statements of operations going forward as the tax consequences of settled share-based payments will be recognized in income tax (expense) benefit 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. These new standards will be effective for the Company beginning October 1, 2018. The Company is currently evaluating the potential impact that Topic 606 may have on its financial position and results of operations. 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. The Company is currently evaluating the potential impact that ASU 2016-18 may have on its statement of cash flows. 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 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, 2019, but early adoption is permissible. The Company is currently evaluating the potential impact that ASU 2017-09 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 Asset21

Fair Value of Financial Assets and Liabilities (Tables)	9 Months Ended
	Jun. 30, 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 June 30, 2017 and September 30, 2016 and indicate the fair value hierarchy of the valuation inputs utilized to determine such fair value: Fair Value Measurements at June 30, 2017 Using: Level 1 Level 2 Level 3 Total Assets: U.S. Treasury notes $ 63,897 $ — $ — $ 63,897 Cash equivalents 7,102 — — 7,102 Corporate bonds — 119,203 — 119,203 Commercial paper — 25,976 — 25,976 U.S. Agency bonds — 3,997 — 3,997 $ 70,999 $ 149,176 $ — $ 220,175 Liabilities: Warrant liability $ — $ — $ 1,291 $ 1,291 Series 1 nonconvertible preferred stock — — 164 164 $ — $ — $ 1,455 $ 1,455 Fair Value Measurements at September 30, 2016 Using: Level 1 Level 2 Level 3 Total Assets: U.S. Treasury notes $ 69,608 $ — $ — $ 69,608 Cash equivalents 15,295 — — 15,295 Corporate bonds — 76,073 — 76,073 Commercial paper — 49,900 — 49,900 U.S. Agency bonds — 30,045 — 30,045 $ 84,903 $ 156,018 $ — $ 240,921 Liabilities: Warrant liability $ — $ — $ 1,251 $ 1,251 Series 1 nonconvertible preferred stock — — 159 159 $ — $ — $ 1,410 $ 1,410
Fair Value Measurements of the Company's Warrant Liability and Series 1 Nonconvertible Preferred Stock	The recurring Level 3 fair value measurements of the Company’s warrant liability and Series 1 nonconvertible preferred stock using probability-weighted discounted cash flow include the following significant unobservable inputs: Range (Weighted Average) June 30, September 30, Unobservable Input 2017 2016 Warrant liability and Series 1 nonconvertible preferred stock Probabilities of payout 0%-60% 0%-60% Periods in which payout is expected to occur 2018 2017-2018 Discount rate 5.25% 4.50%
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, 2016 $ 1,251 $ 159 Increase in fair value 40 5 Balance, June 30, 2017 $ 1,291 $ 164

Marketable Securities (Tables)

Marketable Securities (Tables)	9 Months Ended
	Jun. 30, 2017
Investments Debt And Equity Securities [Abstract]
Fair Value of Available-for-Sale Marketable Securities by Type of Security	As of June 30, 2017 and September 30, 2016, the fair value of available-for-sale marketable securities, by type of security, was as follows: June 30, 2017 Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value Corporate bonds $ 119,298 $ 7 $ (102 ) $ 119,203 U.S. Treasury notes 64,010 — (113 ) 63,897 Commercial paper 25,976 — — 25,976 U.S. Agency bonds 4,008 — (11 ) 3,997 $ 213,292 $ 7 $ (226 ) $ 213,073 September 30, 2016 Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value Corporate bonds $ 76,077 $ 27 $ (31 ) $ 76,073 U.S. Treasury notes 69,579 38 (9 ) 69,608 Commercial paper 49,900 — — 49,900 U.S. Agency bonds 30,040 15 (10 ) 30,045 $ 225,596 $ 80 $ (50 ) $ 225,626

Accrued Expenses and Other Lo23

Accrued Expenses and Other Long-Term Liabilities (Tables)	9 Months Ended
	Jun. 30, 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 June 30, 2017 and September 30, 2016: June 30, September 2017 2016 Accrued expenses: Accrued preclinical and clinical expenses $ 2,024 $ 899 Accrued payroll and related expenses 2,002 2,384 Accrued professional fees 639 393 Accrued vendor manufacturing 452 441 Capital lease obligation 75 73 Accrued other 442 322 $ 5,634 $ 4,512 Other long-term liabilities: Uncertain tax positions $ 1,109 $ 745 Accrued rent expense 711 696 Capital lease obligation 402 458 Asset retirement obligation 172 143 $ 2,394 $ 2,042

Stock-Based Awards (Tables)

Stock-Based Awards (Tables)	9 Months Ended
	Jun. 30, 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 June 30, 2017: Shares Issuable Under Options Weighted Average Exercise Price Weighted Average Remaining Contractual Term in years Aggregate Intrinsic Value Outstanding as of September 30, 2016 1,895,456 $ 28.75 7.6 $ 7,369 Granted 559,019 30.04 Exercised (41,789 ) 6.36 Forfeited (132,655 ) 18.20 Outstanding as of June 30, 2017 2,280,031 $ 30.09 7.6 $ 17,347 Options vested and expected to vest as of June 30, 2017 2,264,139 $ 30.08 7.6 $ 9,358 Options exercisable as of June 30, 2017 1,259,717 $ 28.06 6.7 $ 12,257
Summary of Restricted Stock Unit Activity	The following table summarizes the restricted stock unit activity for the year-to-date period ending June 30, 2017: Restricted Stock Units Weighted Average Grant Date Fair Value Unvested at September 30, 2016 — $ — Granted 112,460 $ 30.00 Vested — $ — Cancelled (2,104 ) $ 30.00 Unvested at June 30, 2017 110,356 $ 30.00
Stock-Based Compensation Expense	During the three and nine months ended June 30, 2017 and 2016 the Company recognized the following stock-based compensation expense: Three Months ended Nine Months Ended June 30, June 30, 2017 2016 2017 2016 Research and development $ 990 $ 790 $ 2,998 $ 2,092 General and administrative 2,112 1,680 6,863 4,752 $ 3,102 $ 2,470 $ 9,861 $ 6,844 Three Months ended Nine Months Ended June 30, June 30, 2017 2016 2017 2016 Stock options $ 2,544 $ 2,270 $ 7,797 $ 6,354 Performance stock units — — 667 — rTSRUs 358 200 905 490 Restricted stock units 200 — 492 — $ 3,102 $ 2,470 $ 9,861 $ 6,844
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 June 30, 2017: Performance Share Units Weighted Average Grant Date Fair Value Relative Total Stockholder Return Units Weighted Average Grant Date Fair Value Unvested at September 30, 2016 48,525 $ 33.70 48,525 $ 31.74 Granted 44,500 $ 35.89 44,500 $ 46.11 Vested (18,820 ) $ 35.47 — $ — Cancelled (4,705 ) $ 35.47 (23,525 ) $ 25.44 Unvested at June 30, 2017 69,500 $ 34.51 69,500 $ 43.07

Net Income (Loss) Per Share (Ta

Net Income (Loss) Per Share (Tables)	9 Months Ended
	Jun. 30, 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 nine months ended June 30, 2017 and 2016 (in thousands, except per share data): Three Months Ended Nine Months Ended June 30, June 30, 2017 2016 2017 2016 Basic net income (loss) per share: Numerator: Net income (loss) $ (8,426 ) $ (1,076 ) $ (18,798 ) $ 23,468 Denominator: Weighted average common shares outstanding—basic 19,081 18,983 19,055 18,893 Net income (loss) per share common share—basic $ (0.44 ) $ (0.06 ) $ (0.99 ) $ 1.24 Diluted net income (loss) per share: Numerator: Net income (loss) $ (8,426 ) $ (1,076 ) $ (18,798 ) $ 23,468 Denominator: Weighted average common shares outstanding—basic 19,081 18,983 19,055 18,893 Dilutive effect of common stock equivalents — — — 330 Weighted average common shares outstanding— diluted 19,081 18,983 19,055 19,223 Net income (loss) per share common share—diluted $ (0.44 ) $ (0.06 ) $ (0.99 ) $ 1.22 Anti-dilutive common stock equivalents excluded from above 2,244 1,620 1,832 1,250

Fair Value of Financial Asset26

Fair Value of Financial Assets and Liabilities - Financial Assets and Liabilities that were Subject to Fair Value Measurement on Recurring Basis (Detail) - USD ($) $ in Thousands	Jun. 30, 2017	Sep. 30, 2016
Assets:
Financial assets measured at fair value	$ 220,175	$ 240,921
Liabilities:
Financial liabilities measured at fair value	1,455	1,410
Warrant Liability [Member]
Liabilities:
Financial liabilities measured at fair value	1,291	1,251
Series 1 Nonconvertible Preferred Stock [Member]
Liabilities:
Financial liabilities measured at fair value	164	159
Level 1 [Member]
Assets:
Financial assets measured at fair value	70,999	84,903
Level 2 [Member]
Assets:
Financial assets measured at fair value	149,176	156,018
Level 3 [Member]
Liabilities:
Financial liabilities measured at fair value	1,455	1,410
Level 3 [Member] | Warrant Liability [Member]
Liabilities:
Financial liabilities measured at fair value	1,291	1,251
Level 3 [Member] | Series 1 Nonconvertible Preferred Stock [Member]
Liabilities:
Financial liabilities measured at fair value	164	159
U.S. Treasury Notes [Member]
Assets:
Financial assets measured at fair value	63,897	69,608
U.S. Treasury Notes [Member] | Level 1 [Member]
Assets:
Financial assets measured at fair value	63,897	69,608
Cash Equivalents [Member]
Assets:
Financial assets measured at fair value	7,102	15,295
Cash Equivalents [Member] | Level 1 [Member]
Assets:
Financial assets measured at fair value	7,102	15,295
Corporate Bonds [Member]
Assets:
Financial assets measured at fair value	119,203	76,073
Corporate Bonds [Member] | Level 2 [Member]
Assets:
Financial assets measured at fair value	119,203	76,073
Commercial Paper [Member]
Assets:
Financial assets measured at fair value	25,976	49,900
Commercial Paper [Member] | Level 2 [Member]
Assets:
Financial assets measured at fair value	25,976	49,900
U.S. Agency Bonds [Member]
Assets:
Financial assets measured at fair value	3,997	30,045
U.S. Agency Bonds [Member] | Level 2 [Member]
Assets:
Financial assets measured at fair value	$ 3,997	$ 30,045

Fair Value of Financial Asset27

Fair Value of Financial Assets and Liabilities - Additional Information (Detail) - USD ($)	9 Months Ended
	Jun. 30, 2017	Jun. 30, 2016
Fair Value Disclosures [Abstract]
Transfers between Level 1, Level 2 and Level 3	$ 0	$ 0

Fair Value of Financial Asset28

Fair Value of Financial Assets and Liabilities - Fair Value Measurements of the Company's Warrant Liability and Series 1 Nonconvertible Preferred Stock (Detail) - Warrant Liability [Member] - Series 1 Nonconvertible Preferred Stock [Member]	9 Months Ended	12 Months Ended
	Jun. 30, 2017	Sep. 30, 2016
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Periods in which payout is expected to occur	2,018
Periods in which payout is expected to occur, beginning		2,017
Periods in which payout is expected to occur, ending		2,018
Discount rate	5.25%	4.50%
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	60.00%	60.00%

Fair Value of Financial Asset29

Fair Value of Financial Assets and Liabilities - Rollforward of Aggregate Fair Values of Warrants (Detail) $ in Thousands	9 Months Ended
	Jun. 30, 2017USD ($)
Series 1 Nonconvertible Preferred Stock [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning Balance	$ 159
Increase in fair value	5
Ending Balance	164
Warrant Liability [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning Balance	1,251
Increase in fair value	40
Ending Balance	$ 1,291

Marketable Securities - Fair Va

Marketable Securities - Fair Value of Available-for-Sale Marketable Securities by Type of Security (Detail) - USD ($) $ in Thousands	Jun. 30, 2017	Sep. 30, 2016
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 213,292	$ 225,596
Gross Unrealized Gains	7	80
Gross Unrealized Losses	(226)	(50)
Fair Value	213,073	225,626
Corporate Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	119,298	76,077
Gross Unrealized Gains	7	27
Gross Unrealized Losses	(102)	(31)
Fair Value	119,203	76,073
U.S. Treasury Notes [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	64,010	69,579
Gross Unrealized Gains		38
Gross Unrealized Losses	(113)	(9)
Fair Value	63,897	69,608
Commercial Paper [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	25,976	49,900
Fair Value	25,976	49,900
U.S. Agency Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	4,008	30,040
Gross Unrealized Gains		15
Gross Unrealized Losses	(11)	(10)
Fair Value	$ 3,997	$ 30,045

Marketable Securities - Additio

Marketable Securities - Additional Information (Detail) - USD ($) $ in Thousands	9 Months Ended
	Jun. 30, 2017	Sep. 30, 2016
Schedule of Available-for-sale Securities [Line Items]
Marketable securities maturing not less than three years, aggregate fair value	$ 43,321	$ 32,119
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	Within 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	Within three years

Accrued Expenses and Other Lo32

Accrued Expenses and Other Long-Term Liabilities - Accrued Expenses and Other Current Liabilities as well as Other Long-Term Liabilities (Detail) - USD ($) $ in Thousands	Jun. 30, 2017	Sep. 30, 2016
Accrued expenses:
Accrued preclinical and clinical expenses	$ 2,024	$ 899
Accrued payroll and related expenses	2,002	2,384
Accrued professional fees	639	393
Accrued vendor manufacturing	452	441
Capital lease obligation	75	73
Accrued other	442	322
Accrued expenses	5,634	4,512
Other long-term liabilities:
Uncertain tax positions	1,109	745
Accrued rent expense	711	696
Capital lease obligation	402	458
Asset retirement obligation	172	143
Other long-term liabilities	$ 2,394	$ 2,042

Ongoing Collaboration Agreeme33

Ongoing Collaboration Agreements - Additional Information (Detail) - USD ($) $ in Thousands	9 Months Ended		128 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Milestone revenue recognized		$ 30,000
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 AbbVie's calendar year net sales
AbbVie [Member] | Additional Funding Agreement Terms [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Potential future milestone	$ 80,000
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			$ 427,000
Milestone Payments [Member] | AbbVie [Member] | Paritaprevir 3-DAA Regimen [Member] | JAPAN
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Milestone revenue recognized		$ 30,000

Warrants to Purchase Series 134

Warrants to Purchase Series 1 Nonconvertible Preferred Stock and Series 1 Nonconvertible Preferred Stock - Additional Information (Detail) - Series 1 Nonconvertible Preferred Stock [Member] - shares	9 Months Ended
	Jun. 30, 2017	Nov. 30, 2010
Class of Warrant or Right [Line Items]
Number of shares issuable upon exercise of the warrants		1,999,989
Warrant expiration date	Oct. 4, 2017

Stock-Based Awards - Summary of

Stock-Based Awards - Summary of Stock Option Activity Including Performance Based Options (Detail) - USD ($) $ / shares in Units, $ in Thousands	9 Months Ended	12 Months Ended
	Jun. 30, 2017	Sep. 30, 2016
Options
Outstanding as of beginning of period	1,895,456
Granted	559,019
Exercised	(41,789)
Forfeited	(132,655)
Outstanding as of end of period	2,280,031	1,895,456
Options vested and expected to vest as of end of period	2,264,139
Options exercisable as of end of period	1,259,717
Weighted Average Exercise Price
Outstanding	$ 28.75
Granted	30.04
Exercised	6.36
Forfeited	18.20
Outstanding	30.09	$ 28.75
Options vested and expected to vest as of end of period	30.08
Options exercisable as of end of period	$ 28.06
Weighted Average Remaining Contractual Term
Outstanding as of end of period	7 years 7 months 6 days	7 years 7 months 6 days
Options vested and expected to vest as of end period	7 years 7 months 6 days
Options exercisable as of end of period	6 years 8 months 12 days
Aggregate Intrinsic Value
Aggregate Intrinsic Value	$ 17,347	$ 7,369
Options vested and expected to vest as of end of period	9,358
Options exercisable as of end of period	$ 12,257

Stock-Based Awards - Additional

Stock-Based Awards - Additional Information (Detail) $ in Thousands	9 Months Ended
	Jun. 30, 2017USD ($)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Aggregate of unrecognized stock-based compensation cost	$ 26,797
Weighted average recognition period	2 years 3 months 18 days
Restricted Stock Units [Member] | Tranche One [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting percentage	50.00%
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 37

Stock-Based Awards - Summary of PSU and rTSRU Activity (Detail)	9 Months Ended
	Jun. 30, 2017$ / sharesshares
PSU [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unvested, beginning balance | shares	48,525
Granted | shares	44,500
Vested | shares	(18,820)
Cancelled | shares	(4,705)
Unvested, ending balance | shares	69,500
Weighted Average Grant Date Fair Value, Unvested beginning balance | $ / shares	$ 33.70
Weighted Average Grant Date Fair Value, Granted | $ / shares	35.89
Weighted Average Grant Date Fair Value, Vested | $ / shares	35.47
Weighted Average Grant Date Fair Value, Cancelled | $ / shares	35.47
Weighted Average Grant Date Fair Value, Unvested ending balance | $ / shares	$ 34.51
Relative Total Stockholder Return Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unvested, beginning balance | shares	48,525
Granted | shares	44,500
Vested | shares	0
Cancelled | shares	(23,525)
Unvested, ending balance | shares	69,500
Weighted Average Grant Date Fair Value, Unvested beginning balance | $ / shares	$ 31.74
Weighted Average Grant Date Fair Value, Granted | $ / shares	46.11
Weighted Average Grant Date Fair Value, Vested | $ / shares	0
Weighted Average Grant Date Fair Value, Cancelled | $ / shares	25.44
Weighted Average Grant Date Fair Value, Unvested ending balance | $ / shares	$ 43.07

Stock-Based Awards - Summary 38

Stock-Based Awards - Summary of Restricted Stock Unit Activity (Detail) - Restricted Stock Units [Member]	9 Months Ended
	Jun. 30, 2017$ / sharesshares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unvested, beginning balance | shares	0
Granted | shares	112,460
Vested | shares	0
Cancelled | shares	(2,104)
Unvested, ending balance | shares	110,356
Weighted Average Grant Date Fair Value, Unvested beginning balance | $ / shares	$ 0
Weighted Average Grant Date Fair Value, Granted | $ / shares	30
Weighted Average Grant Date Fair Value, Vested | $ / shares	0
Weighted Average Grant Date Fair Value, Cancelled | $ / 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		9 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	$ 3,102	$ 2,470	$ 9,861	$ 6,844
Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	2,544	2,270	7,797	6,354
Performance Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense			667
rTSRUs [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	358	200	905	490
Restricted Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	200		492
Research and Development [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	990	790	2,998	2,092
General and Administrative [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	$ 2,112	$ 1,680	$ 6,863	$ 4,752

Net Income (Loss) Per Share - B

Net Income (Loss) Per Share - Basic and Diluted Net Income (Loss) Per Share Attributable to Common Stockholders (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Basic net income (loss) per share:
Net income (loss)	$ (8,426)	$ (1,076)	$ (18,798)	$ 23,468
Weighted average common shares outstanding—basic	19,081	18,983	19,055	18,893
Net income (loss) per share common share—basic	$ (0.44)	$ (0.06)	$ (0.99)	$ 1.24
Diluted net income (loss) per share:
Net income (loss)	$ (8,426)	$ (1,076)	$ (18,798)	$ 23,468
Weighted average common shares outstanding—basic	19,081	18,983	19,055	18,893
Dilutive effect of common stock equivalents				330
Weighted average common shares outstanding— diluted	19,081	18,983	19,055	19,223
Net income (loss) per share common share—diluted	$ (0.44)	$ (0.06)	$ (0.99)	$ 1.22
Anti-dilutive common stock equivalents excluded from above	2,244	1,620	1,832	1,250

Net Income (Loss) Per Share - A

Net Income (Loss) Per Share - Additional Information (Detail) - shares	3 Months Ended		9 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Shares excluded from the computation of diluted net income (loss) per share	2,244,000	1,620,000	1,832,000	1,250,000
Common Stock Equivalents [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Shares excluded from the computation of diluted net income (loss) per share			139,000

Income Taxes - Additional Infor

Income Taxes - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016	Sep. 30, 2016
Income Tax Disclosure [Abstract]
Income tax (expense) benefit	$ 4,103	$ (434)	$ 9,210	$ (11,720)
Effective income tax rate			32.90%	33.30%
Federal statutory income tax rate			35.00%	35.00%
Unrecognized tax benefits	$ 1,109		$ 1,109		$ 745

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Detail) - USD ($) $ in Thousands	9 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Sep. 30, 2016
Commitments And Contingencies Disclosure [Abstract]
Office lease expiration period	Sep. 30, 2022
Rent expense	$ 1,519	$ 1,519
Outstanding letter of credit	608		$ 608
Restricted cash	608		$ 608
Tenant improvement allowance	$ 598

Subsequent Events - Additional

Subsequent Events - Additional Information (Detail) - USD ($) $ in Thousands	1 Months Ended	9 Months Ended
	Aug. 09, 2017	Jun. 30, 2016
Subsequent Event [Line Items]
Milestone payments earned		$ 30,000
Subsequent Event | Milestone Payments [Member] | AbbVie [Member] | MAVIRET [Member] | European Union and U.S [Member]
Subsequent Event [Line Items]
Milestone payments earned	$ 65,000