Enanta Pharmaceuticals (ENTA) 10-K 11 Dec 15 2015 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($)	12 Months Ended
	Sep. 30, 2015	Nov. 30, 2015	Mar. 31, 2015
Document And Entity Information [Abstract]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Sep. 30, 2015
Document Fiscal Year Focus	2,015
Document Fiscal Period Focus	FY
Trading Symbol	ENTA
Entity Registrant Name	ENANTA PHARMACEUTICALS INC
Entity Central Index Key	1,177,648
Current Fiscal Year End Date	--09-30
Entity Well-known Seasoned Issuer	No
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No
Entity Filer Category	Accelerated Filer
Entity Common Stock, Shares Outstanding		18,795,071
Entity Public Float			$ 572,279,471

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Sep. 30, 2015	Sep. 30, 2014
Current assets:
Cash and cash equivalents	$ 21,726	$ 30,699
Short-term marketable securities	123,479	60,065
Accounts receivable	15,289	1,724
Unbilled receivables	433	2,770
Deferred tax assets	1,447	11,123
Prepaid expenses and other current assets	8,267	1,594
Total current assets	170,641	107,975
Property and equipment, net	5,886	1,803
Long-term marketable securities	64,238	41,003
Deferred tax assets	4,640	4,198
Restricted cash	608	436
Total assets	246,013	155,415
Current liabilities:
Accounts payable	1,543	1,874
Accrued expenses and other current liabilities	3,962	2,872
Income taxes payable	1,199
Total current liabilities	6,704	4,746
Warrant liability	1,276	1,584
Other long-term liabilities	1,713	229
Total liabilities	$ 9,856	6,761
Commitments and contingencies (Note 12)
Stockholders' equity:
Common stock; $0.01 par value; 100,000,000 shares authorized; 18,716,834 and 18,803,390 shares issued and 18,716,834 and 18,594,574 shares outstanding at September 30, 2015 and 2014, respectively	$ 187	188
Additional paid-in capital	229,957	221,580
Treasury stock, at par value; no shares at September 30, 2015 and 208,816 shares at September 30, 2014		(2)
Accumulated other comprehensive income (loss)	33	(100)
Retained earnings (accumulated deficit)	5,980	(73,012)
Total stockholders' equity	236,157	148,654
Total liabilities and stockholders' equity	246,013	155,415
Series 1 Nonconvertible Preferred Stock [Member]
Current liabilities:
Series 1 nonconvertible preferred stock	$ 163	$ 202

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - $ / shares	Sep. 30, 2015	Sep. 30, 2014
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	18,716,834	18,803,390
Common stock, shares outstanding	18,716,834	18,594,574
Treasury stock, shares	0	208,816

Consolidated Statements of Oper

Consolidated Statements of Operations - USD ($)	12 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2013
Revenue:
Milestone payments	$ 125,000,000	$ 40,000,000	$ 26,000,000
Royalties	34,077,000
Other	1,803,000	7,741,000	6,053,000
Total revenue	160,880,000	47,741,000	32,053,000
Operating expenses:
Research and development	23,189,000	18,740,000	16,841,000
General and administrative	13,543,000	10,016,000	6,183,000
Total operating expenses	36,732,000	28,756,000	23,024,000
Income from operations	124,148,000	18,985,000	9,029,000
Other income:
Interest income	968,000	467,000	248,000
Interest expense	(8,000)	(18,000)	(31,000)
Change in fair value of warrant liability and Series 1 nonconvertible preferred stock, net	347,000	(166,000)	381,000
Total other income (expense), net	1,307,000	283,000	598,000
Income before income taxes	125,455,000	19,268,000	9,627,000
Income tax (expense) benefit	(46,463,000)	15,170,000	0
Net income	78,992,000	34,438,000	9,627,000
Accretion of redeemable convertible preferred stock to redemption value			(2,526,000)
Net income attributable to participating securities			(13,670,000)
Net income (loss) attributable to common stockholders	$ 78,992,000	$ 34,438,000	$ (6,569,000)
Net income (loss) per share attributable to common stockholders:
Basic	$ 4.23	$ 1.88	$ (0.67)
Diluted	$ 4.09	$ 1.80	$ (0.67)
Weighted average common shares outstanding:
Basic	18,673,484	18,354,791	9,788,039
Diluted	19,294,634	19,185,228	9,788,039

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2013
Statement of Comprehensive Income [Abstract]
Net income	$ 78,992	$ 34,438	$ 9,627
Other comprehensive income (loss):
Net unrealized gains (losses) on marketable securities, net of tax of $20, $0 and $0	133	(98)	(12)
Total other comprehensive income (loss)	133	(98)	(12)
Comprehensive income	$ 79,125	$ 34,340	$ 9,615

Consolidated Statements of Com6

Consolidated Statements of Comprehensive Income (Parenthetical) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2013
Statement of Comprehensive Income [Abstract]
Net unrealized gains (losses) on marketable securities, tax	$ 20	$ 0	$ 0

Consolidated Statements of Chan

Consolidated Statements of Changes in Redeemable and Convertible Preferred Stock and Stockholders' Equity (Deficit) - USD ($) $ in Thousands	Total	Series C, D, E,F and G Redeemable Convertible Preferred Stock [Member]	Series A and B Convertible Preferred Stock [Member]	Common Stock [Member]	Additional Paid-in Capital [Member]	Treasury Stock [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Retained Earnings (Accumulated Deficit) [Member]
Beginning Balance at Sep. 30, 2012	$ (115,353)	$ 158,955	$ 327	$ 13		$ (2)	$ 10	$ (115,374)
Beginning Balance, Shares at Sep. 30, 2012		43,115,343	566,450	1,343,147		(208,816)
Exercise of stock options	559			$ 5	$ 554
Exercise of stock options, Shares				538,575
Compensation expense related to stock options	1,063				1,063
Accretion of redeemable convertible preferred stock to redemption value	(2,526)	$ 2,526			(823)			(1,703)
Conversion of preferred stock to common stock	161,808	$ (161,481)	$ (327)	$ 117	161,691
Conversion of preferred stock into common, Shares		(43,115,343)	(566,450)	11,656,875
Issuance of common stock upon initial public offering	59,892			$ 46	59,846
Issuance of common stock upon initial public offering, Shares				4,600,000
Issuance costs	(4,590)				(4,590)
Other comprehensive income (loss)	(12)						(12)
Net income	9,627							9,627
Ending Balance at Sep. 30, 2013	110,468			$ 181	217,741	$ (2)	(2)	(107,450)
Ending Balance, Shares at Sep. 30, 2013				18,138,597		(208,816)
Exercise of stock options	1,054			$ 7	1,047
Exercise of stock options, Shares				664,793
Compensation expense related to stock options	2,682				2,682
Income tax benefit from stock option exercises	110				110
Other comprehensive income (loss)	(98)						(98)
Net income	34,438							34,438
Ending Balance at Sep. 30, 2014	148,654			$ 188	221,580	$ (2)	(100)	(73,012)
Ending Balance, Shares at Sep. 30, 2014				18,803,390		(208,816)
Exercise of stock options	$ 726			$ 1	725
Exercise of stock options, Shares	122,260			122,260
Compensation expense related to stock options	$ 5,838				5,838
Income tax benefit from stock option exercises	1,814				1,814
Other comprehensive income (loss)	133						133
Retirement of treasury stock				$ (2)		$ 2
Retirement of treasury stock, shares				(208,816)		208,816
Net income	78,992							78,992
Ending Balance at Sep. 30, 2015	$ 236,157			$ 187	$ 229,957		$ 33	$ 5,980
Ending Balance, Shares at Sep. 30, 2015				18,716,834

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2013
Cash flows from operating activities
Net income	$ 78,992	$ 34,438	$ 9,627
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization expense	639	352	221
Non-cash interest expense		8	31
Change in fair value of warrant liability and Series 1 nonconvertible preferred stock	(347)	166	(381)
Stock-based compensation expense	5,838	2,682	1,063
Gain on sale of marketable securities	(4)	(3)
Gain on disposal of property and equipment	(31)	(3)	(100)
Premium on marketable securities	(3,042)	(2,002)	(1,811)
Amortization of premium on marketable securities	2,244	2,120	1,262
Deferred income taxes	11,028	(15,211)
Income tax benefit from exercise of stock options	(1,814)	(110)
Change in operating assets and liabilities:
Accounts receivable	(13,565)	(916)	241
Unbilled receivables	2,337	(1,986)	1,109
Prepaid expenses and other current assets	(6,680)	568	(307)
Other assets			22
Accounts payable	(543)	399	115
Accrued expenses	(227)	(183)	(285)
Income taxes payable	1,199
Deferred revenue		(10)	(7)
Other long-term liabilities	649	(130)	(147)
Net cash provided by operating activities	76,673	20,179	10,653
Cash flows from investing activities
Purchases of property and equipment	(2,336)	(1,028)	(606)
Proceeds from sales of property and equipment	9	3
Purchases of marketable securities	(196,304)	(98,405)	(115,888)
Sales of marketable securities	2,210	8,421	5,453
Maturities of marketable securities	108,407	91,506	41,825
Change in restricted cash	(172)
Net cash provided by (used in) investing activities	(88,186)	497	(69,216)
Cash flows from financing activities
Proceeds from initial public offering, net of underwriting discounts and commissions			59,892
Proceeds from exercise of stock options	726	1,054	559
Payments of initial public offering costs			(3,540)
Income tax benefit from exercise of stock options	1,814	110
Net cash provided by financing activities	2,540	1,164	56,911
Net increase (decrease) in cash and cash equivalents	(8,973)	21,840	(1,652)
Cash and cash equivalents at beginning of period	30,699	8,859	10,511
Cash and cash equivalents at end of period	21,726	30,699	8,859
Supplemental disclosure of cash flow information:
Cash paid for income taxes	40,072	148
Supplemental disclosure of noncash financing activities:
Accretion of redeemable convertible preferred stock to redemption value			2,526
Conversion of preferred stock into common stock			161,808
Exercise of Series 1 warrants into Series 1 nonconvertible preferred stock		206
Non-cash items:
Fixed assets financed through capital lease	598
Fixed assets financed by landlord	239
Purchases of fixed assets included in accounts payable and accrued expenses	1,562
Series 1 Nonconvertible Preferred Stock [Member]
Adjustments to reconcile net income to net cash provided by operating activities:
Change in fair value of warrant liability and Series 1 nonconvertible preferred stock	$ (347)	$ 166	$ (381)

Nature of the Business

Nature of the Business	12 Months Ended
	Sep. 30, 2015
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Nature of the Business	1. Nature of the Business Enanta Pharmaceuticals, Inc. (the “Company”), incorporated in Delaware in 1995, is a 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 has developed novel protease and NS5A inhibitors for treatment of hepatitis C virus (“HCV”) infection. The Company also has programs to develop cyclophilin and nucleotide polymerase inhibitors targeted against HCV and also has a focus area in non-alcoholic steatohepatitis (“NASH”). Additionally, the Company has programs to discover new chemical entities, or compounds, for the treatment of other diseases. 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, 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 approval, prior to commercialization. These efforts require significant amounts of additional capital, adequate personnel infrastructure, and extensive compliance reporting capabilities.

Summary of Significant Accounti

Summary of Significant Accounting Policies	12 Months Ended
	Sep. 30, 2015
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	2. Summary of Significant Accounting Policies Basis of Presentation The accompanying consolidated financial statements include those of the Company and its subsidiary, Enanta Pharmaceuticals Security Corporation, after elimination of all intercompany accounts and transactions. The accompanying consolidated financial statements have been prepared in conformity with accounting principles generally accepted in the United States of America (“GAAP”). Use of Estimates The preparation of consolidated financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, the disclosure of contingent assets and liabilities at the date of the consolidated financial statements, and the reported amounts of revenues and expenses during the reporting period. Significant estimates and assumptions reflected in these consolidated financial statements include, but are not limited to, management’s judgments 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; the useful lives of property and equipment; and the accounting for income taxes, including uncertain tax positions and the valuation of net deferred tax assets. Estimates are periodically reviewed in light of changes in circumstances, facts and experience. Actual results could differ from the Company’s estimates. Cash Equivalents and Marketable Securities The Company considers all short-term, highly liquid investments with original maturities of ninety days or less at acquisition date to be cash equivalents. Marketable securities with original maturities of greater than 90 days and remaining maturities of less than one year from the balance sheet date are classified as short-term marketable securities. Marketable securities with remaining maturities of greater than one year from the balance sheet date are classified as long-term marketable securities. The Company classifies all of its marketable securities as available-for-sale. All marketable securities are held with one investment manager. The Company continually evaluates the credit ratings of its investment portfolio and underlying securities. The Company invests in accordance with its investment policy and invests at the date of purchase in securities with a rating of A3 or higher and A– or higher according to Moody’s and S&P, respectively. The Company reports available-for-sale investments at fair value as of each balance sheet date and records any unrealized gains and losses as a component of stockholders’ equity. The cost of securities sold is determined on a specific identification basis, and realized gains and losses are included in other income (expense) within the consolidated statement of operations. If any adjustment to fair value reflects a decline in the value of the investment, the Company considers available evidence to evaluate the extent to which the decline is “other than temporary” and reduces the investment to fair value through a charge to the statement of operations. There were no such adjustments necessary during the years ended September 30, 2015, 2014 or 2013. Restricted Cash As of September 30, 2015 and 2014, the Company had outstanding a letter of credit collateralized by a money market account of $608 and $436, respectively, to the benefit of the landlord of the Company’s current building lease. This amount was classified as long-term restricted cash as of September 30, 2015 and 2014. Concentration of Credit Risk and of Significant Customers and Suppliers Financial instruments that potentially expose the Company to concentrations of credit risk consist primarily of cash, cash equivalents, marketable securities, accounts receivable and unbilled receivables. The Company has all cash and investment balances at one accredited financial institution, in amounts that exceed federally insured limits. The Company does not believe that it is subject to unusual credit risk beyond the normal credit risk associated with commercial banking relationships. The Company has historically generated all of its revenue from its collaborative research and license agreements and a U.S. government contract (see Note 7). As of September 30, 2015, accounts receivable and unbilled receivables consisted of amounts due from the Company’s collaborators and under the U.S. government contract (see Note 7). As of September 30, 2014, accounts receivable and unbilled receivables consisted solely of amounts due under the U.S. government contract. The Company is completely dependent on third-party manufacturers for product supply for preclinical research activities in its non-partnered programs. In particular, the Company relies and expects to continue to rely exclusively on several manufacturers to supply it with its requirements for the active pharmaceutical ingredients related to these programs. These research programs would be adversely affected by a significant interruption in the supply of it active pharmaceutical ingredients. Fair Value Measurements Certain assets and liabilities are carried at fair value under GAAP. Fair value is defined as the exchange price that would be received for an asset or paid to transfer a liability (an exit price) in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants on the measurement date. Valuation techniques used to measure fair value must maximize the use of observable inputs and minimize the use of unobservable inputs. A fair value hierarchy based on three levels of inputs, of which the first two are considered observable and the last is considered unobservable, is used to measure fair value: • Level 1—Quoted prices in active markets for identical assets or liabilities. • Level 2—Observable inputs (other than Level 1 quoted prices) such as quoted prices in active markets for similar assets or liabilities, quoted prices in markets that are not active for identical or similar assets or liabilities, or other inputs that are observable or can be corroborated by observable market data. • Level 3—Unobservable inputs that are supported by little or no market activity and that are significant to determining the fair value of the assets or liabilities, including pricing models, discounted cash flow methodologies and similar techniques. The Company’s cash equivalents and marketable securities assets and its warrant and Series 1 nonconvertible preferred stock liabilities are carried at fair value determined according to the fair value hierarchy described above (see Note 3). The carrying values of accounts receivable and unbilled receivables, accounts payable and accrued expenses approximate their fair value due to the short-term nature of these assets and liabilities. Property and Equipment Property and equipment are stated at cost less accumulated depreciation or amortization. Depreciation and amortization expense is recognized using the straight-line method over the following estimated useful lives: Laboratory and office equipment 5 years Leasehold improvements Shorter of life of lease or estimated useful life Purchased software 3 years Computer equipment 3 years Furniture 7 years Expenditures for repairs and maintenance of assets are charged to expense as incurred. Costs of major additions and betterments are capitalized and depreciated on a straight-line basis over their useful lives. Upon retirement or sale, the cost and related accumulated depreciation or amortization of assets disposed of are removed from the accounts and any resulting gain or loss is included in income from operations. Impairment of Long-Lived Assets The Company reviews long-lived assets, including property and equipment, for impairment whenever events or changes in business circumstances indicate that the carrying amount of the assets may not be fully recoverable. Factors that the Company considers in deciding when to perform an impairment review include significant underperformance of the business in relation to expectations, significant negative industry or economic trends, and significant changes or planned changes in the use of the assets. If an impairment review is performed to evaluate a long-lived asset for recoverability, the Company compares forecasts of undiscounted cash flows expected to result from the use and eventual disposition of the long-lived asset to its carrying value. An impairment loss would be recognized when estimated undiscounted future cash flows expected to result from the use of an asset are less than its carrying amount. The impairment loss would be based on the excess of the carrying value of the impaired asset over its fair value, determined based on discounted cash flows. To date, the Company has not recorded any impairment losses on long-lived assets. Revenue Recognition The Company’s revenue has been generated primarily through collaborative research and license agreements. The terms of these agreements contain multiple deliverables, which may include (i) licenses, (ii) research and development activities, and (iii) participation in joint research and development steering committees. The terms of these agreements may include nonrefundable upfront license fees, payments for research and development activities, payments based upon the achievement of certain milestones, and royalty payments based on product sales derived from the collaboration. In all instances, revenue is recognized only when the price is fixed or determinable, persuasive evidence of an arrangement exists, delivery has occurred or the services have been rendered, collectibility of the resulting receivable is reasonably assured, and the Company has fulfilled its performance obligations under the contract. On October 1, 2011, the Company adopted Accounting Standards Update No. 2009-13, Multiple-Deliverable Revenue Arrangements In determining the separate units of accounting, the Company evaluates whether the license has standalone value to the collaborator based on consideration of the relevant facts and circumstances for each arrangement. Factors considered in this determination include the research and development capabilities of the collaborator and the availability of relevant research expertise in the marketplace. In addition, the Company considers whether or not (i) the collaborator can use the license for its intended purpose without the receipt of the remaining deliverables, (ii) the value of the license is dependent on the undelivered items, and (iii) the collaborator or other vendors can provide the undelivered items. For all periods presented, whenever the Company determines that an element is delivered over a period of time, revenue is recognized using either a proportional performance model or a straight-line model over the period of performance, which is typically the research and development term. Full-time equivalents (“FTEs”) are typically used as the measure of performance. At each reporting period, the Company reassesses its cumulative measure of performance and makes appropriate adjustments, if necessary. The Company recognizes revenue using the proportional performance model whenever the Company can make reasonably reliable estimates of the level of effort required to complete its performance obligations under an arrangement. Revenue recognized under the proportional performance model at each reporting period is determined by multiplying the total expected payments under the contract (excluding royalties and payments contingent upon achievement of milestones) by the ratio of the level of effort incurred to date to the estimated total level of effort required to complete the performance obligations under the arrangement. Revenue is limited to the lesser of the cumulative amount of payments received or the cumulative amount of revenue earned, as determined using the proportional performance model as of each reporting period. Alternatively, if the Company cannot make reasonably reliable estimates of the level of effort required to complete its performance obligations under an arrangement, then revenue under the arrangement is recognized on a straight-line basis over the period expected to complete the Company’s performance obligations. If and when a contingent milestone payment is earned, the additional consideration to be received is allocated to the separate units of accounting in the arrangement based on their relative selling prices at the inception of the arrangement. Revenue is limited to the lesser of the cumulative amount of payments received or the cumulative amount of revenue earned, as determined on a straight-line basis as of the period end date. If the Company cannot reasonably estimate when its performance obligation period ends, then revenue is deferred until the Company can reasonably estimate when the performance obligation period ends. Royalty revenue is recognized based on contractual terms when reported sales are reliably measurable and collectability is reasonably assured, provided that there are no performance obligations then remaining. During the years ended September 30, 2015, 2014 and 2013, the Company also generated revenue from a government contract, under which the Company is reimbursed for certain allowable costs for the funded project. Revenue from the government contract is recognized when the related service is performed. The related costs incurred by the Company under the government contract are included in research and development expenses in the statements of operations. This contract was completed in August 2015. Amounts received prior to satisfying all revenue recognition criteria are recorded as deferred revenue in the accompanying consolidated balance sheets. Amounts not expected to be recognized as revenue within the next twelve months of the consolidated balance sheet date are classified as long-term deferred revenue. In the event that a collaborative research and license agreement is terminated and the Company then has no further performance obligations, the Company recognizes as revenue any amounts that had not previously been recorded as revenue but were classified as deferred revenue at the date of such termination. Research and Development Costs Research and development costs are expensed as incurred. Included in research and development costs are wages, stock-based compensation and benefits of employees, third-party license fees and other operational costs related to the Company’s research and development activities, including facility-related expenses and external costs of outside contractors engaged to conduct both preclinical and clinical studies. The Company also includes in research and development expense the costs to complete the Company’s obligations under research collaborations. Patent Costs All patent-related costs incurred in connection with filing and prosecuting patent applications are recorded as general and administrative expenses as incurred, as recoverability of such expenditures is uncertain. Accounting for Stock-Based Compensation The Company measures all stock options and other stock-based awards granted to employees at the fair value on the date of the grant. The Company uses the Black-Scholes option-pricing model in the valuation of its stock options. The Company uses Monte-Carlo simulation in order to calculate fair value of market-based awards. The fair value of the awards is recognized as expense, net of estimated forfeitures, over the requisite service period, which is generally the vesting period of the respective award. The straight-line method of expense recognition is applied to all awards with service-only conditions. The Company records compensation expense related to performance-based awards when performance-based targets are deemed to be probable of being achieved. The Company classifies stock-based compensation expense in the statements of operations in the same manner in which the award recipient’s payroll costs are classified. Income Taxes The Company accounts for income taxes using the asset and liability method, which requires the recognition of deferred tax assets and liabilities for the expected future tax consequences of events that have been recognized in the financial statements or in the Company’s tax returns. Deferred taxes are determined based on the difference between the financial reporting and tax basis of assets and liabilities using enacted tax rates in effect in the years in which the differences are expected to reverse. Changes in deferred tax assets and liabilities are recorded in the provision for income taxes. The Company assesses the likelihood that its deferred tax assets will be recovered from future taxable income and, to the extent it believes, based upon the weight of available evidence, that it is more likely than not that all or a portion of deferred tax assets will not be realized, a valuation allowance is established through a charge to income tax expense. Potential for recovery of deferred tax assets is evaluated by estimating the future taxable profits expected and considering prudent and feasible tax planning strategies. The Company accounts for uncertainty in income taxes recognized in the financial statements by applying a two-step process to determine the amount of tax benefit to be recognized. First, the tax position must be evaluated to determine the likelihood that it will be sustained upon external examination by the taxing authorities. If the tax position is deemed more-likely-than-not to be sustained, the tax position is then assessed to determine the amount of benefit to recognize in the financial statements. The amount of the benefit that may be recognized is the largest amount that has a greater than 50% likelihood of being realized upon ultimate settlement. The provision for income taxes includes the effects of any resulting tax reserves, or unrecognized tax benefits, that are considered appropriate as well as the related net interest and penalties. Net Income per Share The Company followed the two-class method when computing net income (loss) per share during periods prior to the IPO when the Company had outstanding shares that met the definition of participating securities. The two-class method was used to determine net income (loss) per share for each class of common and participating securities according to dividends declared or accumulated and participation rights in undistributed earnings. The two-class method required income available to common stockholders for the period to be allocated between common and participating securities based upon their respective rights to receive dividends as if all income for the period had been distributed. The Company’s redeemable convertible preferred shares and convertible preferred shares contractually entitled the holders of such shares to participate in dividends, but did not contractually require the holders of such shares to participate in losses of the Company. Accordingly, in periods in which the Company had participating securities and reported a net loss or a net loss attributable to common stockholders resulting from preferred stock dividends or accretion, net losses were not allocated to participating securities. Basic net income (loss) per share attributable to common stockholders is computed by dividing the net income (loss) attributable to common stockholders by the weighted average number of shares of common stock outstanding for the period. Diluted net income (loss) attributable to common stockholders is computed by adjusting net income (loss) attributable to common stockholders to reallocate undistributed earnings based on the potential impact of dilutive securities, including outstanding stock options and outstanding warrants. Diluted net income (loss) per share attributable to common stockholders is computed by dividing the diluted net income (loss) attributable to common stockholders by the weighted average number of common shares outstanding for the period, including potential dilutive common shares assuming the dilutive effect of outstanding stock options and outstanding warrants. Market-based awards are included in diluted EPS to the extent they would have vested if the period end date was the market criteria measurement date. Segment Data The Company manages its operations as a single segment for the purposes of assessing performance and making operating decisions. The Company is a biotechnology company focused on discovering and developing small molecule drugs for the treatment of viral infections and liver diseases. Revenue is generated exclusively from transactions occurring in the United States, and all assets are held in the United States. Comprehensive Income (Loss) Comprehensive income (loss) includes net income (loss) as well as other changes in stockholders’ equity (deficit) that result from transactions and economic events other than those with stockholders. The Company’s only element of other comprehensive income (loss) is unrealized gains and losses on available-for-sale marketable securities. Recently Issued and Adopted Accounting Pronouncements In May, 2014, the Financial Accounting Standards Board (the “FASB”) issued Accounting Standards Update (“ASU”) No. 2014-09, Revenue from Contracts with Customers In November 2015, the FASB issued ASU No. 2015-17, Balance Sheet Classification of Deferred Taxes 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 financial statements upon adoption.

Fair Value of Financial Assets

Fair Value of Financial Assets and Liabilities	12 Months Ended
	Sep. 30, 2015
Fair Value Disclosures [Abstract]
Fair Value of Financial Assets and Liabilities	3. Fair Value of Financial Assets and Liabilities The following tables present information about the Company’s financial assets and liabilities that were subject to fair value measurement on a recurring basis as of September 30, 2015 and 2014 and indicate the fair value hierarchy of the valuation inputs utilized to determine such fair value: Fair Value Measurements as of September 30, 2015 Using: Level 1 Level 2 Level 3 Total Assets: Cash equivalents $ 21,327 $ — $ — $ 21,327 Corporate bonds — 151,020 — 151,020 U.S. Agency bonds — 36,697 — 36,697 $ 21,327 $ 187,717 $ — $ 209,044 Liabilities: Warrant liability $ — $ — $ 1,276 $ 1,276 Series 1 nonconvertible preferred stock — — 163 163 $ — $ — $ 1,439 $ 1,439 Fair Value Measurements as of September 30, 2014 Using: Level 1 Level 2 Level 3 Total Assets: Cash equivalents $ 30,239 $ — $ — $ 30,239 Commercial paper — 7,499 — 7,499 Corporate bonds — 88,056 — 88,056 U.S. Agency bonds — 5,513 — 5,513 $ 30,239 $ 101,068 $ — $ 131,307 Liabilities: Warrant liability $ — $ — $ 1,584 $ 1,584 Series 1 nonconvertible preferred stock — — 202 202 $ — $ — $ 1,786 $ 1,786 Cash equivalents at September 30, 2015 and 2014 consist of money market funds. During the years ended September 30, 2015, 2014 and 2013, there were no transfers between Level 1, Level 2 and Level 3. As of September 30, 2015 and 2014, respectively, the warrant liability was comprised of the value of the warrants for the purchase of Series 1 nonconvertible preferred stock measured at fair value. As of September 30, 2015 the outstanding Series 1 nonconvertible preferred stock was also measured at fair value. The fair value of both of these instruments was based on significant inputs not observable in the market, which represented 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. The fair value of outstanding warrants to purchase our Series 1 nonconvertible preferred stock was $1,276 and $1,584 at September 30, 2015 and 2014, respectively. The fair value of Series 1 nonconvertible preferred stock was $163 and $202 as of September 30, 2015 and 2014, respectively. Changes in the fair value of the warrant liability and Series 1 nonconvertible preferred stock are recognized 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: September 30, 2015 Unobservable Input Range Warrant liability and Series 1 nonconvertible preferred stock Probabilities of payout 5% - 60% Periods in which payout is expected to occur 2016 - 2017 Discount rate 4.25% September 30, 2014 Unobservable Input Range Warrant liability and Series 1 nonconvertible preferred stock Probabilities of payout 10% - 90% Periods in which payout is expected to occur 2015 - 2016 Discount rate 4.25% 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: Balance, September 30, 2012 $ 2,001 Decrease in fair value (381 ) Balance, September 30, 2013 1,620 Warrants exercised (206 ) Series 1 nonconvertible preferred stock issued 206 Increase in fair value 166 Balance, September 30, 2014 1,786 Decrease in fair value (347 ) Balance, September 30, 2015 $ 1,439

Marketable Securities

Marketable Securities	12 Months Ended
	Sep. 30, 2015
Investments, Debt and Equity Securities [Abstract]
Marketable Securities	4. Marketable Securities As of September 30, 2015 and 2014, the fair value of available-for-sale marketable securities by type of security was as follows: September 30, 2015 Amortized Cost Gross Unrealized Gross Unrealized Fair Value Corporate bonds $ 151,012 $ 77 $ (69 ) $ 151,020 U.S. Agency bonds 36,652 45 — 36,697 $ 187,664 $ 122 $ (69 ) $ 187,717 September 30, 2014 Amortized Cost Gross Unrealized Gross Unrealized Fair Value Commercial paper $ 7,499 $ — $ — $ 7,499 Corporate bonds 88,156 14 (114 ) 88,056 U.S. Agency bonds 5,513 — — 5,513 $ 101,168 $ 14 $ (114 ) $ 101,068 At September 30, 2015, marketable securities consisted of investments that mature within one year, with the exception of certain corporate and U.S. Agency bonds, which have maturities between one and three years and an aggregate fair value of $64,238.

Property and Equipment

Property and Equipment	12 Months Ended
	Sep. 30, 2015
Property, Plant and Equipment [Abstract]
Property and Equipment	5. Property and Equipment Property and equipment consisted of the following as of September 30, 2015 and 2014: September 30, 2015 2014 Laboratory and office equipment $ 5,907 $ 4,829 Leasehold improvements 1,290 300 Purchased software 443 414 Computer equipment 137 111 Furniture 496 284 Construction in progress 1,889 — 10,162 5,938 Less: Accumulated depreciation and amortization (4,276 ) (4,135 ) $ 5,886 $ 1,803 Depreciation and amortization expense was $639, $352 and $221 for the years ended September 30, 2015, 2014 and 2013, respectively. During the years ended September 30, 2015, 2014 and 2013, assets with a cost of $518, $554 and $420, respectively, were sold or disposed of, resulting in gains of $31, $3 and $100, respectively.

Accrued Expenses, Other Current

Accrued Expenses, Other Current Liabilities and Other Long-Term Liabilities	12 Months Ended
	Sep. 30, 2015
Payables and Accruals [Abstract]
Accrued Expenses, Other Current Liabilities and Other Long-Term Liabilities	6. Accrued Expenses, Other Current Liabilities and Other Long-Term Liabilities Accrued expenses, other current liabilities and other long-term liabilities consisted of the following as of September 30, 2015 and 2014: September 30, 2015 2014 Accrued expenses and other current liabilities: Accrued payroll and related expenses $ 1,622 $ 1,275 Accrued fixed asset purchases 1,307 — Accrued professional fees 338 436 Accrued preclinical and clinical expenses 237 493 Capital lease obligation 69 — Accrued vendor manufacturing 18 116 Accrued third-party license fee — 240 Accrued other 371 312 $ 3,962 $ 2,872 Other long-term liabilities: Accrued rent expense $ 628 $ 153 Capital lease obligation 529 — Uncertain tax positions 448 — Asset retirement obligation 108 76 $ 1,713 $ 229 In connection with the current lease, as amended, the Company spent $598 of tenant improvement allowance provided by the landlord and accounted for as a capital lease obligation.

Collaboration Agreements

Collaboration Agreements	12 Months Ended
	Sep. 30, 2015
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Collaboration Agreements	7. Collaboration Agreements AbbVie Collaboration On November 27, 2006, the Company entered into a Collaborative Development and License Agreement (the “AbbVie Agreement”) with Abbott Laboratories to identify, develop and commercialize HCV NS3 and NS3/4A protease inhibitor compounds, including paritaprevir (also known as ABT-450). The agreement was assigned by Abbott to AbbVie Inc. on January 1, 2013 in connection with Abbott’s transfer of its research-based pharmaceuticals business to AbbVie. Under the terms of the AbbVie Agreement, as amended, AbbVie paid to the Company upfront license payments and FTE reimbursements to fund research activities. The Company is also eligible to receive milestone payments for the successful development by AbbVie of one or more HCV compounds as well as annually, tiered per product, royalties 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 net sales by AbbVie allocated to the collaboration’s protease inhibitors. The Company determined that the deliverables under the AbbVie Agreement included (i) the non-exclusive, royalty-free, worldwide research license and the exclusive, royalty-bearing development and commercialization license, (ii) the research services, and (iii) a commitment to participate on a steering committee, all of which were to be delivered over a three-year period. The Company concluded that the license did not have standalone value as it was dependent, in part, upon the Company’s continuing involvement in the HCV protease inhibitor research and its involvement in the joint steering committee. Additionally, the undelivered items, including the Company’s participation in the joint steering committee, which was considered participatory due to its decision making responsibilities, and the research services, did not have VSOE or VOE of fair value. Therefore, the license, the research services, and the joint steering committee participation were treated as a single unit of accounting. Accordingly, all amounts received were deferred, and revenue was recognized using the proportional performance model over the period during which the Company performed research services in connection with the AbbVie Agreement, as amended. Subsequent to the research and evaluation period which ended in June 2011, all decisions related to the development, commercialization and marketing have been made by AbbVie. The Company has the right to continue to attend the joint steering committee meetings to monitor the development and marketing plans; however, the Company has no decision making rights. As such, the joint steering committee commitment became protective in nature as of June 16, 2011. During the years ended September 30, 2015, 2014 and 2013, the Company received $125,000, $40,000 and $15,000 in milestone payments under the AbbVie Agreement as a result of AbbVie’s development and commercialization of a regimen that included paritaprevir. From commencement of the collaboration, through September 30, 2015, the Company has received a total of $319,000 under the AbbVie Agreement consisting of an upfront license payment, research funding, milestone payments, royalties and preferred stock financing. As of September 30, 2015, the Company was eligible to receive an additional milestone payment of $30,000 upon AbbVie’s achievement of commercialization regulatory approval of a paritaprevir-containing regimen in Japan, which was earned in November 2015. The Company is also eligible to receive additional milestone payments totaling up to $80,000 upon AbbVie’s achievement of similar commercialization regulatory approval milestones in the U.S. and other selected world markets for each additional protease inhibitor commercialized by AbbVie. The Company is also eligible to receive annually tiered royalties per 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 net sales by AbbVie allocated to the collaboration’s protease inhibitors separately. Under the terms of the agreement, as amended in October 2014, 30% of net sales of a 3-DAA regimen containing paritaprevir will be allocated to paritaprevir, and 45% of net sales of a 2-DAA regimen containing paritaprevir will be allocated to paritaprevir. For ABT-493, the next generation protease inhibitor currently being developed by AbbVie, 50% of net sales of a 2-DAA regimen containing ABT-493 will be allocated to ABT-493, and 33 1 3 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 achieved by AbbVie. The Company had the option, but not the obligation, to co-develop and share in the profit of any product in the United States that is developed as a result of the AbbVie Agreement. This option for the first compound (paritaprevir) expired in 2011 and the option for the second compound (ABT-493) expired in 2014 without the Company choosing to exercise either option. The Company has no further obligations in regard to the AbbVie Agreement and will evaluate future options as they arise. Royalties owed to the Company under the agreement can be reduced by AbbVie in certain circumstances, including (i) if AbbVie exercises its right to license or otherwise acquire rights to intellectual property controlled by a third party where a product could not be legally developed or commercialized in a country without the third-party intellectual property right, (ii) where a product developed under the collaboration agreement is sold in a country and not covered by a valid patent claim in such country, and (iii) where sales of a generic product are equal to at least a specified percentage of AbbVie’s market share of a product in a country. AbbVie’s obligation to pay royalties on a product developed under the agreement expires on a country-by-country basis upon the later of (i) the date of expiration of the last of the licensed patents with a valid claim covering the product in the applicable country, or (ii) ten years after the first commercial sale of the product in the applicable country. Subject to certain exceptions, a party’s rights and obligations under the agreement continues until (i) such time as AbbVie is no longer developing a product candidate or (ii) if, as of the time AbbVie is no longer developing any product candidates, AbbVie is commercializing any other protease inhibitor product, such time as all royalty terms for all covered products and all co-development terms for all co-developed products have ended. Accordingly, the final expiration date of the agreement is currently indeterminable. Either party may terminate the agreement for cause in the event of a material breach, subject to prior notice and the opportunity to cure, or in the event of the other party’s bankruptcy. Additionally, AbbVie may terminate the agreement for any reason upon specified prior notice. If the Company terminates the agreement for cause or AbbVie terminates without cause, any licenses and other rights granted to AbbVie will terminate and AbbVie will be deemed to have granted the Company (i) a non-exclusive, perpetual, fully paid, worldwide, royalty-free license, with the right to sublicense, under AbbVie’s intellectual property used in any product candidate, and (ii) an exclusive (even as to AbbVie), perpetual, fully paid, worldwide, royalty-free license, with the right to sublicense, under AbbVie’s interest in any joint intellectual property rights to develop product candidates resulting from covered compounds and to commercialize any products derived from such compounds. Upon the Company’s request, AbbVie will also transfer to the Company all right, title and interest in any related product trademarks, regulatory filings and clinical trials. If AbbVie terminates the agreement for the Company’s uncured breach, the milestone and royalty payments payable by AbbVie may be reduced, the licenses granted to AbbVie will remain in place, the Company will be deemed to have granted AbbVie an exclusive license under the Company’s interest in joint intellectual property, AbbVie will continue to have the right to commercialize any covered products, and all rights and licenses granted to the Company by AbbVie will terminate. Novartis Collaboration Under the terms of a 2012 license and collaboration agreement to develop an NS5A inhibitor with Novartis (the “Novartis Agreement”), the Company received an upfront payment of $34,442 million in fiscal 2012 and a commitment to fund research at an agreed amount for one year. The Company recognized the upfront license payment upon receipt. During the year ended September 30, 2013, the Company recognized total revenue of $12,675 under the Novartis Agreement, of which $10,894 was attributable to license fees and $1,781 was attributable to the performance of research services. No revenue was recognized under the agreement in fiscal 2014 or 2015. On September 30, 2014 the Company and Novartis entered into an amendment to the Novartis Agreement to return to the Company full rights to its NS5A inhibitor program, including EDP-239, and to transition the proof-of-concept study of EDP-239 to the Company. The Company owes no future payments to Novartis in connection with this transfer. NIAID Contract On September 30, 2011, the Company entered into a contract with the National Institute of Allergy and Infectious Diseases (“NIAID”), a division of the National Institutes of Health (“NIH”), providing development funding to the Company for the preclinical and clinical development of a bridged bicyclic antibiotic to be used as a medical countermeasure against multiple biodefense Category A and B bacteria. In February 2015, NIAID and the Company amended the contract to provide for completion in August 2015 and to decrease the total committed contract funding. The Company has received payments of $18,672 under the NIAID contract through September 30, 2015. The Company recognized revenue under this contract as development services were performed in accordance with the funding agreement. During the year ended September 30, 2015, the Company recognized revenue of $1,803, under this contract. As of September 30, 2015, $955 was invoiced but unpaid and included in accounts receivable, $433 was unbilled and included in unbilled receivables. During the year ended September 30, 2014, the Company recognized revenue of $7,741, under this contract, of which $1,724 was invoiced but unpaid and included in accounts receivable and $2,770 was unpaid and included in unbilled receivables at September 30, 2014. During the year ended September 30, 2013, the Company recognized revenue of $4,378, under this contract. The contract was completed in August 2015 upon the Company’s delivery of the study report for the Phase 1 clinical study.

Stockholders' Equity

Stockholders' Equity	12 Months Ended
	Sep. 30, 2015
Equity [Abstract]
Stockholders' Equity	8. Stockholders’ Equity On March 1, 2013, the Company effected an increase in the number of authorized shares of its common stock from 70,000,000 to 100,000,000 shares. On March 1, 2013, the Company effected a 1-for-4.31 reverse stock split of its issued and outstanding shares of common stock and a proportional adjustment to the existing conversion ratio for each series of redeemable convertible preferred stock and convertible preferred stock. Accordingly, all share and per share amounts for all periods presented in these financial statements and notes thereto have been adjusted retroactively, where applicable, to reflect the reverse stock split and adjustment of the preferred share conversion ratios. On March 26, 2013 the Company completed an initial public offering of its common stock, which resulted in the sale of 4,600,000 shares. The Company received net proceeds from the IPO of $59,892 based upon the price of $14.00 per share and after deducting underwriting discounts and commissions paid by the Company. Upon the closing of the initial public offering, all outstanding shares of the Company’s redeemable convertible preferred stock and convertible preferred stock were converted into 11,656,875 shares of common stock. Each share of common stock entitles the holder to one vote on all matters submitted to a vote of the Company’s stockholders. Common stockholders are entitled to receive such dividends as may be declared by the board of directors, if any. The Company retired all 208,186 shares of treasury stock effective September 30, 2015 which resulted in a decrease in the same number of issued shares of common stock.

Series 1 Nonconvertible Preferr

Series 1 Nonconvertible Preferred Stock	12 Months Ended
	Sep. 30, 2015
Text Block [Abstract]
Series 1 Nonconvertible Preferred Stock	9. Series 1 Nonconvertible Preferred Stock The Company’s Certificate of Incorporation authorizes the issuance of up to 1,999,989 shares of Series 1 nonconvertible preferred Stock (the “Series 1 nonconvertible preferred”) at a par value of $0.01 per share. Holders of Series 1 nonconvertible preferred stock are not entitled to receive dividends. In the event of any liquidation, deemed liquidation, dissolution or winding up of the Company, the Series 1 nonconvertible preferred stockholders are entitled to receive in preference to all other stockholders, an amount equal to $1.00 per share, adjusted for any stock dividends, stock splits or reclassifications. Series 1 nonconvertible preferred holders will not be entitled to vote unless required by the Company pursuant to the laws of the State of Delaware. The Company may redeem the Series 1 nonconvertible preferred stock with the approval of the holders of a majority of the outstanding shares of Series 1 nonconvertible preferred at a redemption price of $1.00 per share. The Company must redeem the stock within 60 days of such election. Shares that are redeemed will be retired or canceled and not reissued by the Company. In October and November 2010, a total of 1,999,989 warrants to purchase Series 1 nonconvertible preferred stock were issued. These warrants expire on October 4, 2017. As these warrants are free-standing financial instruments that may require the Company to transfer assets upon exercise, up to a maximum of $2,000, these warrants are classified as liabilities. The warrants had a fair value upon issuance of $1,280. The Company is required to remeasure the fair value of these preferred stock warrants at each reporting date, with any adjustments recorded within the change in fair value of warrant liability included in other income (expense) in the statement of operations. On February 5, 2014, 225,408 warrants were exercised resulting in the net issuance of 223,153 shares of Series 1 nonconvertible preferred stock, which were outstanding at September 30, 2015 and 2014. The remeasurement of the warrants and Series 1 nonconvertible preferred stock resulted in income of $347, expense of $166 and income of $361 for the years ended September 30, 2015, 2014 and 2013, respectively. As of September 30, 2015 and 2014, the total fair value of the Series 1 nonconvertible preferred stock was $163 and $202, respectively. As of September 30, 2015 and September 30, 2014, the total fair value of the Series 1 nonconvertible preferred stock warrants was $1,276 and $1,584, respectively. If all outstanding warrants to purchase the Series 1 nonconvertible preferred stock are exercised, the resulting outstanding shares of Series 1 nonconvertible preferred stock will carry an aggregate $2,000 liquidation preference that is superior to the common stock and any other classes of preferred stock then outstanding. The following table summarizes the Company’s warrant activity since October 1, 2012: Series 1 Weighted Outstanding, as of September 30, 2012 1,999,989 $ 0.01 Granted — Expired — Exercised — Outstanding, as of September 30, 2013 1,999,989 $ 0.01 Granted — Expired — Exercised (225,408 ) Outstanding, as of September 30, 2014 1,774,581 $ 0.01 Granted — Expired — Exercised — Outstanding, as of September 30, 2015 1,774,581 $ 0.01

Stock-Based Awards

Stock-Based Awards	12 Months Ended
	Sep. 30, 2015
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Stock-Based Awards	10. Stock-Based Awards The Company’s 2012 Equity Incentive Plan (the “2012 Plan”) permits the Company to sell or issue common stock or restricted common stock or to grant incentive stock options or nonqualified stock options for the purchase of common stock, restricted stock units, performance units, stock appreciation rights or other cash incentive awards, to employees, members of the board of directors and consultants of the Company. The number of shares of common stock that may be issued under the 2012 Plan is subject to increase by the number of shares forfeited under any options terminated and not exercised under the previous plan, known as the 1995 Equity Incentive Plan as well as by a number of additional shares on the first day of each fiscal year by the lowest amount among the following: (i) 3% of the Company’s outstanding shares of common stock as of that date, (ii) 2,088,167 shares of common stock, or (iii) an amount determined by the board of directors. On October 1, 2014, the number of shares of common stock that might be issued under the 2012 Plan was increased by 557,863 shares. As of September 30, 2015, 444,173 shares remained available for future grant. Options granted under the 2012 Plan to non-executive employees generally vest quarterly over four years and expire after ten years; options granted to executive employees generally vest over one to four years; and options granted to the board of directors vest over two to three years. The 2012 Plan replaces and is the successor to the 1995 Equity Incentive Plan (the “1995 Plan”). The 1995 Plan provided for the Company to sell or issue common stock or restricted common stock, or to grant incentive stock options or nonqualified stock options for the purchase of common stock, to employees, members of the board of directors and consultants of the Company. Sales, issuances or grants of shares entitle the holder to purchase common stock from the Company, for a specified exercise price, during a period specified by the applicable equity award agreement. Upon the closing of the Company’s initial public offering, all remaining shares reserved for issuance under the 1995 Plan were transferred to the 2012 Plan and no further awards will be made under the 1995 Plan. Under the Company’s Employee Stock Purchase Plan (“ESPP”) a total of 185,614 shares of common stock are reserved for issuance. As of September 30, 2015, the Company had not commenced any offering under the ESPP and no plan shares have been issued. The Company applies the fair value recognition provisions for all stock-based awards granted or modified. In the case of service-based awards, the compensation cost is recorded over the requisite service period of the award on the straight-line method based on the grant-date fair value. The requisite service period for service-based awards is generally four years, with restrictions lapsing evenly over the period. In March 2013, the Company granted to certain executives 167,052 options that vest upon the achievement of certain performance-based targets. The grant date fair value of these options was $2,479. During the year ended September 30, 2014, one performance-based target was achieved and the Company recorded compensation expense of $206 related to that target. No compensation expense related to these options was recognized during the years ended September 30, 2015 and 2013 as none of the performance-based targets was deemed to be probable of being achieved. Stock Option Valuation The fair value of each stock option grant is estimated on the date of grant using the Black-Scholes option-pricing model. To date the Company lacks sufficient company-specific historical volatility information. Therefore, it estimates its expected stock volatility based on the historical volatility of a selected group of publicly traded peer companies and expects to continue to do so until such time as it has adequate historical data regarding the volatility of its own traded stock price. The expected term of the Company’s stock options has been determined utilizing the “simplified” method for awards that qualify as “plain-vanilla” options. The risk-free interest rate is determined by reference to the U.S. Treasury yield curve in effect at the time of grant of the award for time periods approximately equal to the expected term of the award. Expected dividend yield is based on the fact that the Company has never paid cash dividends and does not expect to pay any cash dividends in the foreseeable future. The relevant data used to determine the value of the stock option grants is as follows, presented on a weighted average basis: Years Ended September 30, 2015 2014 2013 Risk-free interest rate 1.85 % 1.89 % 1.05 % Expected term (in years) 6.03 6.06 6.09 Expected volatility 74 % 75 % 73 % Expected dividend yield 0 % 0 % 0 % The Company recognizes compensation expense for only the portion of awards that are expected to vest. In developing a forfeiture rate estimate, the Company has considered its historical experience to estimate pre-vesting forfeitures for service-based awards. The impact of a forfeiture rate adjustment will be recognized in full in the period of adjustment, and if the actual forfeiture rate is materially different from the Company’s estimate, the Company may be required to record adjustments to stock-based compensation expense in future periods. As required by the 1995 Plan and 2012 Plan, the exercise price for awards granted is not to be less than the fair value of common shares as estimated by the Company as of the date of grant. For the periods prior to the March 2013 IPO, the Company valued its common stock by taking into consideration its most recently available valuation of common shares performed by management and the board of directors as well as additional factors which may have changed since the date of the most recent contemporaneous valuation through the date of grant. For the periods after the IPO, the Company based fair value of its common stock on the quoted market price. The following table summarizes stock option activity for the year ended September 30, 2015: Shares Weighted Weighted Aggregate Outstanding as of September 30, 2014 1,389,437 $ 15.39 7.2 $ 33,573 Granted 526,755 42.36 Exercised (122,260 ) 5.94 Forfeited (41,922 ) 32.24 Outstanding as of September 30, 2015 1,752,010 $ 23.76 7.2 $ 25,093 Options vested and expected to vest as of September 30, 2015 1,576,413 $ 24.71 7.1 $ 21,369 Options exercisable as of September 30, 2015 854,183 $ 14.58 5.7 $ 18,852 The aggregate intrinsic value of options is calculated as the difference between the exercise price of the options and the fair value of the Company’s common stock for those shares that had exercise prices lower than the fair value of the Company’s common stock. The aggregate intrinsic value of stock options exercised was $4,827, $3,219 and $7,574 during the years ended September 30, 2015, 2014 and 2013, respectively. The Company received cash proceeds from the exercise of stock options of $726, $1,054 and $559 during the years ended September 30, 2015, 2014 and 2013, respectively. The weighted average grant date fair value of options granted during the years ended September 30, 2015, 2014 and 2013 was $27.77, $19.98 and $9.16, respectively. The Company recorded stock-based compensation expense for the years ended September 30, 2015, 2014 and 2013 in the following expense categories: Years Ended September 30, 2015 2014 2013 Research and development $ 1,644 $ 762 $ 393 General and administrative 4,194 1,920 670 $ 5,838 $ 2,682 $ 1,063 As of September 30, 2015, the Company had an aggregate of $18,399 of unrecognized stock-based compensation cost, which is expected to be recognized over a weighted average period of 2.8 years. Market and Performance-based Stock Unit Awards In February 2015, the Company awarded certain executive officers a total of 41,800 share units consisting of 20,900 performance share units, or PSUs, and 20,900 relative total shareholder return units, or rTSRUs. 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. The PSUs will vest and result in issuance, or settlement, of common shares for each recipient, based upon the recipient’s continued employment with the Company and the Company’s achievement of specified research and development milestones on or before December 31, 2016. The aggregate grant date fair value of the 20,900 PSUs ranges between $0 and $1,501. During the year ended September 30, 2015, the Company recorded no compensation expense related to the PSU awards as none of the performance-based targets were probable of being achieved during this period. The rTSRUs will vest and result in the issuance of common stock for each recipient based upon the recipient’s continuing employment with the Company and the relative ranking of the total shareholder return, or TSR, of the Company’s common stock in relation to the TSR of the component companies in the NASDAQ Biotech Index over a two-year period based on a comparison of average closing stock prices in December 2014 and December 2016. The number of market-based rTSRUs awarded represents the target number of shares of common stock that may be earned; however, the actual number of shares that may be earned ranges from 0% to 200% of the target number. The Company used a Monte Carlo simulation model to estimate that the grant-date fair value of the rTSRUs was $554. The table below sets forth the assumptions used to value the awards and the estimated grant-date fair value: Risk-free interest rate 0.61 % Dividend yield 0 % Expected volatility 55.66 % Remaining performance period (years) 1.86 Estimated fair value per share of rTSRUs granted $ 26.51 The fair value related to the rTSRUs will be recorded as compensation expense over the period from date of grant to December 2016 regardless of whether the target relative total shareholder returns are reached. During the year ended September 30, 2015, the Company recorded $181 in expense related to rTSRUs.

Net Income (Loss) Per Share

Net Income (Loss) Per Share	12 Months Ended
	Sep. 30, 2015
Earnings Per Share [Abstract]
Net Income (Loss) Per Share	11. Net Income (Loss) Per Share Basic and diluted net income (loss) per share attributable to common stockholders was calculated as follows for the years ended September 30, 2015, 2014 and 2013: Years Ended September 30, 2015 2014 2013 Basic net income (loss) per share attributable to common stockholders: Numerator: Net income $ 78,992 $ 34,438 $ 9,627 Accretion of redeemable convertible preferred stock to redemption value — — (2,526 ) Net income attributable to participating securities — — (13,670 ) Net income (loss) attributable to common stockholders $ 78,992 $ 34,438 $ (6,569 ) Denominator: Weighted average common shares outstanding—basic 18,673,484 18,354,791 9,788,039 Net income (loss) per share attributable to common stockholders—basic $ 4.23 $ 1.88 $ (0.67 ) Years Ended September 30, 2015 2014 2013 Diluted net income (loss) per share attributable to common stockholders: Numerator: Net income $ 78,992 $ 34,438 $ 9,627 Accretion of redeemable convertible preferred stock to redemption value — — (2,526 ) Net income attributable to participating securities — — (13,670 ) Net income (loss) attributable to common stockholders—diluted $ 78,992 $ 34,438 $ (6,569 ) Denominator: Weighted average common shares outstanding—basic 18,673,484 18,354,791 9,788,039 Dilutive effect of common stock equivalents 621,150 830,437 — Weighted average common shares outstanding—diluted 19,294,634 19,185,228 9,788,039 Net income (loss) per share attributable to common stockholders—diluted $ 4.09 $ 1.80 $ (0.67 ) Stock options and awards for the purchase of 604,632, 330,430 and 1,713,313 weighted average shares were excluded from the computation of diluted net income per share attributable to common stockholders for the years ended September 30, 2015, 2014 and 2013, respectively, because those options had an anti-dilutive impact due to either the net loss attributable to common stockholders incurred for the period or to the assumed proceeds per share using the treasury stock method being greater than the average fair value of the Company’s common shares for those periods.

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Sep. 30, 2015
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	12. Commitments and Contingencies Leases The Company had an office and laboratory lease that was effective from fiscal 2011 to 2018. During the year ended September 30, 2015, the Company amended the lease to expand the rented space and extend the lease term through September 2022. Payment escalations specified in the lease agreement, as amended, are accrued such that rent expense is recognized on a straight-line basis over the term of occupancy. The Company incurred rent expense of $1,326 for the year ended September 30, 2015 and $948, for each of the years ended September 30, 2014 and 2013. Future minimum lease payments as of September 30, 2015 are as follows: Years Ended September 30, Operating Capital Total 2016 $ 1,958 $ 68 $ 2,026 2017 2,010 73 2,083 2018 2,062 79 2,141 2019 2,117 85 2,202 2020 2,172 93 2,265 Thereafter 4,322 200 4,522 Total $ 14,641 $ 598 $ 15,239 In connection with the current lease, the Company had an outstanding letter of credit in the amounts of $608 and $436 as of September 30, 2015 and 2014, respectively, collateralized by a money market account. As of September 30, 2015 and 2014, the Company classified these amounts as restricted cash. Additionally the amended lease included a $598 tenant improvement allowance from the landlord, which allowance is accounted for as a capital lease obligation. Intellectual Property Licenses The Company has a non-exclusive intellectual property license agreement with a licensor of research technology. Under the 2012 agreement, the Company is required to pay the third party licensor an upfront license fee of $350 and additional license fees of $250 on the first anniversary, $250 on the second anniversary and $200 on the third anniversary of the agreement. In addition, the Company is required to pay (1) annual maintenance fees of $105 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 $50 in each circumstance in which the Company provides the licensed intellectual property to one of its collaborators with the prior consent of the licensor. As of October 1, 2012, the Company had recorded liabilities totaling $995 related to the agreement. During the years ended September 30, 2015, 2014 and 2013, the Company paid $200, $250 and $350, respectively, under the agreement. During the year ended September 30, 2013, the Company obtained an amendment to an existing license agreement to extend rights to patents previously licensed for one of its programs for use in its other HCV research. Under the amended agreement, the Company is obligated to pay milestones totaling up to $5,000, plus low single digit royalties, for each HCV product it develops and for which it obtains regulatory approval outside of its collaboration with AbbVie or any other collaboration it may enter into in the future with a partner that has already licensed these patents. In the same period, the Company paid a milestone payment of $500 under this amended agreement. 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 may 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, could 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 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 September 30, 2015 or 2014.

Income Taxes

Income Taxes	12 Months Ended
	Sep. 30, 2015
Income Tax Disclosure [Abstract]
Income Taxes	13. Income Taxes Income before income taxes for all periods presented is from domestic operations, which are the Company’s only operations. During the years ended September 30, 2015, 2014 and 2013, the Company recorded a provision or a benefit for income taxes as follows: Years Ended September 30, 2015 2014 2013 Current income tax expense: Federal $ 35,040 $ — $ — State 2,172 151 — Deferred income tax expense (benefit): Federal 7,371 (13,048 ) — State 1,880 (2,273 ) — $ 46,463 $ (15,170 ) $ — For the years ended September 30, 2015 and 2014, the Company recorded an income tax provision of $46,463 and an income tax benefit of $15,170, respectively. During the year ended September 30, 2013 no provision for income taxes was recorded due primarily to the Company’s use of net operating loss carryforwards to offset the income before income taxes of $9,627 generated in that period. As the deferred tax assets for those utilized net operating loss carryforwards had previously been recorded with a full valuation allowance, the use of the net operating loss carryforwards in the period resulted in an income tax benefit being recognized, which offset the tax provision recorded as a result of the income before income taxes generated. During fiscal 2014, the Company reassessed the need for a valuation allowance against its deferred tax assets. The Company concluded from the reassessment that it was more likely than not that the Company would be able to realize its deferred tax assets primarily as a result of recent profitability and forecasted future profits resulting from future expected milestone payments and on-going royalty payments from its AbbVie collaboration. Accordingly, the Company released its valuation allowance of $22,892 in fiscal 2014. The effective tax rate for the year ended September 30, 2015 was 37.0% and differs from the federal statutory rate of 35% primarily due to state income taxes, changes in estimates related to research and development tax credits for fiscal years prior to 2015 and certain expenditures which are permanently not deductible for tax purposes. The effective tax rate for the year ended September 30, 2014 was (78.7)% and differs from the federal statutory rate of 35% primarily due to a change in estimate as to the Company’s ability to realize the benefits of its net operating loss carry-forwards and research and development tax credits resulting in a reduction of the Company’s valuation allowance against deferred tax assets in the amount of $22,892, as well as changes in estimates related to the fiscal 2014 research and development tax credits, and certain expenditures which are permanently not deductible for tax purposes. The effective tax rate benefit for the fiscal year ended September 30, 2013 was 0% and differs from the federal statutory tax rate of 34% primarily because the Company had available tax loss carryforwards and other deferred tax assets to offset its taxable income in that period. A reconciliation of the U.S. federal statutory income tax rate to the Company’s effective income tax rate is as follows: Years Ended September 30, 2015 2014 2013 Federal statutory income tax rate 35.0 % 35.0 % 34.0 % State taxes, net of federal benefit 2.6 5.5 5.5 Federal research and development tax credit (0.1 ) (0.5 ) (2.5 ) Change in deferred tax asset valuation allowance — (118.8 ) (51.0 ) Change in statutory rate 0.3 (2.1 ) — Other (0.8 ) 2.2 14.0 Effective income tax rate 37.0 % (78.7 )% 0.0 % Net deferred tax assets as of September 30, 2015 and 2014 consisted of the following: September 30, 2015 2014 Net operating loss carryforwards $ — $ 2,952 Tax credit carryforwards — 5,920 Capitalized research and development expenses 2,903 4,756 Other temporary differences 3,204 1,693 Gross deferred tax assets 6,107 15,321 Valuation allowance — — Deferred tax assets $ 6,107 $ 15,321 As of September 30, 2014, the Company had net operating loss carryforwards for federal and state income tax purposes of $0 and $8,433, respectively, which were utilized entirely in fiscal 2015. The Company also had available research and development tax credit and other credit carryforwards for federal and state income tax purposes of $4,481 and $2,214, respectively, which were similarly entirely utilized in fiscal 2015. 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 2008 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 had an unrecognized tax benefit of $448 and $0 as of September 30, 2015 and 2014, 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.

401(k) Plan

401(k) Plan	12 Months Ended
	Sep. 30, 2015
Postemployment Benefits [Abstract]
401(k) Plan	14. 401(k) Plan The Company has a 401(k) plan. This plan covers substantially all employees who meet minimum age and service requirements. Under the terms of the plan, the Company contributed on an annual basis up to 2% of an employee base salary up to a maximum of $4 per employee. During the year ended September 30, 2014, the plan was amended to allow the Company to contribute on an annual basis up to 3% of an employee’s base salary up to a maximum of $8 per employee. During the years ended September 30, 2015, 2014 and 2013, the Company recognized $382, $180 and $90, respectively, of expense related to its contributions to this plan.

Selected Quarterly Financial Da

Selected Quarterly Financial Data (unaudited)	12 Months Ended
	Sep. 30, 2015
Quarterly Financial Information Disclosure [Abstract]
Selected Quarterly Financial Data (unaudited)	15. Selected Quarterly Financial Data (unaudited) Quarterly financial information for fiscal 2015, 2014 and 2013 is presented in the following table, in thousands, except per share data: 2015 Quarter Ended December 31, 2014 March 31, 2015 June 30, 2015 September 30, 2015 Revenue $ 77,498 $ 57,367 $ 11,599 $ 14,416 Operating expenses 7,288 8,806 9,896 10,742 Other income, net 301 210 287 509 Income tax (expense) benefit (28,502 ) (20,018 ) 428 1,629 Net income 42,009 28,753 2,418 5,812 Net income per share attributable to common shareholders—basic $ 2.26 $ 1.54 $ 0.13 $ 0.30 Net income per share attributable to common shareholders—diluted $ 2.18 $ 1.49 $ 0.13 $ 0.29 2014 Quarter Ended December 31, 2013 March 31, 2014 June 30, 2014 September 30, 2014 Revenue $ 893 $ 2,160 $ 42,051 $ 2,637 Operating expenses 6,350 7,287 7,156 7,963 Other income (expense), net 87 (76 ) 36 236 Income tax benefit — — 15,122 48 Net income (loss) (5,370 ) (5,203 ) 50,053 (5,042 ) Net income (loss) per share attributable to common shareholders—basic $ (0.30 ) $ (0.28 ) $ 2.70 $ (0.27 ) Net income (loss) per share attributable to common shareholders—diluted $ (0.30 ) $ (0.28 ) $ 2.61 $ (0.27 )

Summary of Significant Accoun24

Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Sep. 30, 2015
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The accompanying consolidated financial statements include those of the Company and its subsidiary, Enanta Pharmaceuticals Security Corporation, after elimination of all intercompany accounts and transactions. The accompanying consolidated financial statements have been prepared in conformity with accounting principles generally accepted in the United States of America (“GAAP”).
Use of Estimates	Use of Estimates The preparation of consolidated financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, the disclosure of contingent assets and liabilities at the date of the consolidated financial statements, and the reported amounts of revenues and expenses during the reporting period. Significant estimates and assumptions reflected in these consolidated financial statements include, but are not limited to, management’s judgments 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; the useful lives of property and equipment; and the accounting for income taxes, including uncertain tax positions and the valuation of net deferred tax assets. Estimates are periodically reviewed in light of changes in circumstances, facts and experience. Actual results could differ from the Company’s estimates.
Cash Equivalents and Marketable Securities	Cash Equivalents and Marketable Securities The Company considers all short-term, highly liquid investments with original maturities of ninety days or less at acquisition date to be cash equivalents. Marketable securities with original maturities of greater than 90 days and remaining maturities of less than one year from the balance sheet date are classified as short-term marketable securities. Marketable securities with remaining maturities of greater than one year from the balance sheet date are classified as long-term marketable securities. The Company classifies all of its marketable securities as available-for-sale. All marketable securities are held with one investment manager. The Company continually evaluates the credit ratings of its investment portfolio and underlying securities. The Company invests in accordance with its investment policy and invests at the date of purchase in securities with a rating of A3 or higher and A– or higher according to Moody’s and S&P, respectively. The Company reports available-for-sale investments at fair value as of each balance sheet date and records any unrealized gains and losses as a component of stockholders’ equity. The cost of securities sold is determined on a specific identification basis, and realized gains and losses are included in other income (expense) within the consolidated statement of operations. If any adjustment to fair value reflects a decline in the value of the investment, the Company considers available evidence to evaluate the extent to which the decline is “other than temporary” and reduces the investment to fair value through a charge to the statement of operations. There were no such adjustments necessary during the years ended September 30, 2015, 2014 or 2013.
Restricted Cash	Restricted Cash As of September 30, 2015 and 2014, the Company had outstanding a letter of credit collateralized by a money market account of $608 and $436, respectively, to the benefit of the landlord of the Company’s current building lease. This amount was classified as long-term restricted cash as of September 30, 2015 and 2014.
Concentration of Credit Risk and of Significant Customers and Suppliers	Concentration of Credit Risk and of Significant Customers and Suppliers Financial instruments that potentially expose the Company to concentrations of credit risk consist primarily of cash, cash equivalents, marketable securities, accounts receivable and unbilled receivables. The Company has all cash and investment balances at one accredited financial institution, in amounts that exceed federally insured limits. The Company does not believe that it is subject to unusual credit risk beyond the normal credit risk associated with commercial banking relationships. The Company has historically generated all of its revenue from its collaborative research and license agreements and a U.S. government contract (see Note 7). As of September 30, 2015, accounts receivable and unbilled receivables consisted of amounts due from the Company’s collaborators and under the U.S. government contract (see Note 7). As of September 30, 2014, accounts receivable and unbilled receivables consisted solely of amounts due under the U.S. government contract. The Company is completely dependent on third-party manufacturers for product supply for preclinical research activities in its non-partnered programs. In particular, the Company relies and expects to continue to rely exclusively on several manufacturers to supply it with its requirements for the active pharmaceutical ingredients related to these programs. These research programs would be adversely affected by a significant interruption in the supply of it active pharmaceutical ingredients.
Fair Value Measurements	Fair Value Measurements Certain assets and liabilities are carried at fair value under GAAP. Fair value is defined as the exchange price that would be received for an asset or paid to transfer a liability (an exit price) in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants on the measurement date. Valuation techniques used to measure fair value must maximize the use of observable inputs and minimize the use of unobservable inputs. A fair value hierarchy based on three levels of inputs, of which the first two are considered observable and the last is considered unobservable, is used to measure fair value: • Level 1—Quoted prices in active markets for identical assets or liabilities. • Level 2—Observable inputs (other than Level 1 quoted prices) such as quoted prices in active markets for similar assets or liabilities, quoted prices in markets that are not active for identical or similar assets or liabilities, or other inputs that are observable or can be corroborated by observable market data. • Level 3—Unobservable inputs that are supported by little or no market activity and that are significant to determining the fair value of the assets or liabilities, including pricing models, discounted cash flow methodologies and similar techniques. The Company’s cash equivalents and marketable securities assets and its warrant and Series 1 nonconvertible preferred stock liabilities are carried at fair value determined according to the fair value hierarchy described above (see Note 3). The carrying values of accounts receivable and unbilled receivables, accounts payable and accrued expenses approximate their fair value due to the short-term nature of these assets and liabilities.
Property and Equipment	Property and Equipment Property and equipment are stated at cost less accumulated depreciation or amortization. Depreciation and amortization expense is recognized using the straight-line method over the following estimated useful lives: Laboratory and office equipment 5 years Leasehold improvements Shorter of life of lease or estimated useful life Purchased software 3 years Computer equipment 3 years Furniture 7 years Expenditures for repairs and maintenance of assets are charged to expense as incurred. Costs of major additions and betterments are capitalized and depreciated on a straight-line basis over their useful lives. Upon retirement or sale, the cost and related accumulated depreciation or amortization of assets disposed of are removed from the accounts and any resulting gain or loss is included in income from operations.
Impairment of Long-Lived Assets	Impairment of Long-Lived Assets The Company reviews long-lived assets, including property and equipment, for impairment whenever events or changes in business circumstances indicate that the carrying amount of the assets may not be fully recoverable. Factors that the Company considers in deciding when to perform an impairment review include significant underperformance of the business in relation to expectations, significant negative industry or economic trends, and significant changes or planned changes in the use of the assets. If an impairment review is performed to evaluate a long-lived asset for recoverability, the Company compares forecasts of undiscounted cash flows expected to result from the use and eventual disposition of the long-lived asset to its carrying value. An impairment loss would be recognized when estimated undiscounted future cash flows expected to result from the use of an asset are less than its carrying amount. The impairment loss would be based on the excess of the carrying value of the impaired asset over its fair value, determined based on discounted cash flows. To date, the Company has not recorded any impairment losses on long-lived assets.
Revenue Recognition	Revenue Recognition The Company’s revenue has been generated primarily through collaborative research and license agreements. The terms of these agreements contain multiple deliverables, which may include (i) licenses, (ii) research and development activities, and (iii) participation in joint research and development steering committees. The terms of these agreements may include nonrefundable upfront license fees, payments for research and development activities, payments based upon the achievement of certain milestones, and royalty payments based on product sales derived from the collaboration. In all instances, revenue is recognized only when the price is fixed or determinable, persuasive evidence of an arrangement exists, delivery has occurred or the services have been rendered, collectibility of the resulting receivable is reasonably assured, and the Company has fulfilled its performance obligations under the contract. On October 1, 2011, the Company adopted Accounting Standards Update No. 2009-13, Multiple-Deliverable Revenue Arrangements In determining the separate units of accounting, the Company evaluates whether the license has standalone value to the collaborator based on consideration of the relevant facts and circumstances for each arrangement. Factors considered in this determination include the research and development capabilities of the collaborator and the availability of relevant research expertise in the marketplace. In addition, the Company considers whether or not (i) the collaborator can use the license for its intended purpose without the receipt of the remaining deliverables, (ii) the value of the license is dependent on the undelivered items, and (iii) the collaborator or other vendors can provide the undelivered items. For all periods presented, whenever the Company determines that an element is delivered over a period of time, revenue is recognized using either a proportional performance model or a straight-line model over the period of performance, which is typically the research and development term. Full-time equivalents (“FTEs”) are typically used as the measure of performance. At each reporting period, the Company reassesses its cumulative measure of performance and makes appropriate adjustments, if necessary. The Company recognizes revenue using the proportional performance model whenever the Company can make reasonably reliable estimates of the level of effort required to complete its performance obligations under an arrangement. Revenue recognized under the proportional performance model at each reporting period is determined by multiplying the total expected payments under the contract (excluding royalties and payments contingent upon achievement of milestones) by the ratio of the level of effort incurred to date to the estimated total level of effort required to complete the performance obligations under the arrangement. Revenue is limited to the lesser of the cumulative amount of payments received or the cumulative amount of revenue earned, as determined using the proportional performance model as of each reporting period. Alternatively, if the Company cannot make reasonably reliable estimates of the level of effort required to complete its performance obligations under an arrangement, then revenue under the arrangement is recognized on a straight-line basis over the period expected to complete the Company’s performance obligations. If and when a contingent milestone payment is earned, the additional consideration to be received is allocated to the separate units of accounting in the arrangement based on their relative selling prices at the inception of the arrangement. Revenue is limited to the lesser of the cumulative amount of payments received or the cumulative amount of revenue earned, as determined on a straight-line basis as of the period end date. If the Company cannot reasonably estimate when its performance obligation period ends, then revenue is deferred until the Company can reasonably estimate when the performance obligation period ends. Royalty revenue is recognized based on contractual terms when reported sales are reliably measurable and collectability is reasonably assured, provided that there are no performance obligations then remaining. During the years ended September 30, 2015, 2014 and 2013, the Company also generated revenue from a government contract, under which the Company is reimbursed for certain allowable costs for the funded project. Revenue from the government contract is recognized when the related service is performed. The related costs incurred by the Company under the government contract are included in research and development expenses in the statements of operations. This contract was completed in August 2015. Amounts received prior to satisfying all revenue recognition criteria are recorded as deferred revenue in the accompanying consolidated balance sheets. Amounts not expected to be recognized as revenue within the next twelve months of the consolidated balance sheet date are classified as long-term deferred revenue. In the event that a collaborative research and license agreement is terminated and the Company then has no further performance obligations, the Company recognizes as revenue any amounts that had not previously been recorded as revenue but were classified as deferred revenue at the date of such termination.
Research and Development Costs	Research and Development Costs Research and development costs are expensed as incurred. Included in research and development costs are wages, stock-based compensation and benefits of employees, third-party license fees and other operational costs related to the Company’s research and development activities, including facility-related expenses and external costs of outside contractors engaged to conduct both preclinical and clinical studies. The Company also includes in research and development expense the costs to complete the Company’s obligations under research collaborations.
Patent Costs	Patent Costs All patent-related costs incurred in connection with filing and prosecuting patent applications are recorded as general and administrative expenses as incurred, as recoverability of such expenditures is uncertain.
Accounting for Stock-Based Compensation	Accounting for Stock-Based Compensation The Company measures all stock options and other stock-based awards granted to employees at the fair value on the date of the grant. The Company uses the Black-Scholes option-pricing model in the valuation of its stock options. The Company uses Monte-Carlo simulation in order to calculate fair value of market-based awards. The fair value of the awards is recognized as expense, net of estimated forfeitures, over the requisite service period, which is generally the vesting period of the respective award. The straight-line method of expense recognition is applied to all awards with service-only conditions. The Company records compensation expense related to performance-based awards when performance-based targets are deemed to be probable of being achieved. The Company classifies stock-based compensation expense in the statements of operations in the same manner in which the award recipient’s payroll costs are classified.
Income Taxes	Income Taxes The Company accounts for income taxes using the asset and liability method, which requires the recognition of deferred tax assets and liabilities for the expected future tax consequences of events that have been recognized in the financial statements or in the Company’s tax returns. Deferred taxes are determined based on the difference between the financial reporting and tax basis of assets and liabilities using enacted tax rates in effect in the years in which the differences are expected to reverse. Changes in deferred tax assets and liabilities are recorded in the provision for income taxes. The Company assesses the likelihood that its deferred tax assets will be recovered from future taxable income and, to the extent it believes, based upon the weight of available evidence, that it is more likely than not that all or a portion of deferred tax assets will not be realized, a valuation allowance is established through a charge to income tax expense. Potential for recovery of deferred tax assets is evaluated by estimating the future taxable profits expected and considering prudent and feasible tax planning strategies. The Company accounts for uncertainty in income taxes recognized in the financial statements by applying a two-step process to determine the amount of tax benefit to be recognized. First, the tax position must be evaluated to determine the likelihood that it will be sustained upon external examination by the taxing authorities. If the tax position is deemed more-likely-than-not to be sustained, the tax position is then assessed to determine the amount of benefit to recognize in the financial statements. The amount of the benefit that may be recognized is the largest amount that has a greater than 50% likelihood of being realized upon ultimate settlement. The provision for income taxes includes the effects of any resulting tax reserves, or unrecognized tax benefits, that are considered appropriate as well as the related net interest and penalties.
Net Income per Share	Net Income per Share The Company followed the two-class method when computing net income (loss) per share during periods prior to the IPO when the Company had outstanding shares that met the definition of participating securities. The two-class method was used to determine net income (loss) per share for each class of common and participating securities according to dividends declared or accumulated and participation rights in undistributed earnings. The two-class method required income available to common stockholders for the period to be allocated between common and participating securities based upon their respective rights to receive dividends as if all income for the period had been distributed. The Company’s redeemable convertible preferred shares and convertible preferred shares contractually entitled the holders of such shares to participate in dividends, but did not contractually require the holders of such shares to participate in losses of the Company. Accordingly, in periods in which the Company had participating securities and reported a net loss or a net loss attributable to common stockholders resulting from preferred stock dividends or accretion, net losses were not allocated to participating securities. Basic net income (loss) per share attributable to common stockholders is computed by dividing the net income (loss) attributable to common stockholders by the weighted average number of shares of common stock outstanding for the period. Diluted net income (loss) attributable to common stockholders is computed by adjusting net income (loss) attributable to common stockholders to reallocate undistributed earnings based on the potential impact of dilutive securities, including outstanding stock options and outstanding warrants. Diluted net income (loss) per share attributable to common stockholders is computed by dividing the diluted net income (loss) attributable to common stockholders by the weighted average number of common shares outstanding for the period, including potential dilutive common shares assuming the dilutive effect of outstanding stock options and outstanding warrants. Market-based awards are included in diluted EPS to the extent they would have vested if the period end date was the market criteria measurement date.
Segment Data	Segment Data The Company manages its operations as a single segment for the purposes of assessing performance and making operating decisions. The Company is a biotechnology company focused on discovering and developing small molecule drugs for the treatment of viral infections and liver diseases. Revenue is generated exclusively from transactions occurring in the United States, and all assets are held in the United States.
Comprehensive Income (Loss)	Comprehensive Income (Loss) Comprehensive income (loss) includes net income (loss) as well as other changes in stockholders’ equity (deficit) that result from transactions and economic events other than those with stockholders. The Company’s only element of other comprehensive income (loss) is unrealized gains and losses on available-for-sale marketable securities.
Recently Issued and Adopted Accounting Pronouncements	Recently Issued and Adopted Accounting Pronouncements In May, 2014, the Financial Accounting Standards Board (the “FASB”) issued Accounting Standards Update (“ASU”) No. 2014-09, Revenue from Contracts with Customers In November 2015, the FASB issued ASU No. 2015-17, Balance Sheet Classification of Deferred Taxes 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 financial statements upon adoption.

Summary of Significant Accoun25

Summary of Significant Accounting Policies (Tables)	12 Months Ended
	Sep. 30, 2015
Accounting Policies [Abstract]
Property and Equipment Estimated Useful Lives	Property and equipment are stated at cost less accumulated depreciation or amortization. Depreciation and amortization expense is recognized using the straight-line method over the following estimated useful lives: Laboratory and office equipment 5 years Leasehold improvements Shorter of life of lease or estimated useful life Purchased software 3 years Computer equipment 3 years Furniture 7 years

Fair Value of Financial Asset26

Fair Value of Financial Assets and Liabilities (Tables)	12 Months Ended
	Sep. 30, 2015
Fair Value Disclosures [Abstract]
Financial Assets and Liabilities that were Subject to Fair Value Measurement on Recurring Basis	The following tables present information about the Company’s financial assets and liabilities that were subject to fair value measurement on a recurring basis as of September 30, 2015 and 2014 and indicate the fair value hierarchy of the valuation inputs utilized to determine such fair value: Fair Value Measurements as of September 30, 2015 Using: Level 1 Level 2 Level 3 Total Assets: Cash equivalents $ 21,327 $ — $ — $ 21,327 Corporate bonds — 151,020 — 151,020 U.S. Agency bonds — 36,697 — 36,697 $ 21,327 $ 187,717 $ — $ 209,044 Liabilities: Warrant liability $ — $ — $ 1,276 $ 1,276 Series 1 nonconvertible preferred stock — — 163 163 $ — $ — $ 1,439 $ 1,439 Fair Value Measurements as of September 30, 2014 Using: Level 1 Level 2 Level 3 Total Assets: Cash equivalents $ 30,239 $ — $ — $ 30,239 Commercial paper — 7,499 — 7,499 Corporate bonds — 88,056 — 88,056 U.S. Agency bonds — 5,513 — 5,513 $ 30,239 $ 101,068 $ — $ 131,307 Liabilities: Warrant liability $ — $ — $ 1,584 $ 1,584 Series 1 nonconvertible preferred stock — — 202 202 $ — $ — $ 1,786 $ 1,786
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: September 30, 2015 Unobservable Input Range Warrant liability and Series 1 nonconvertible preferred stock Probabilities of payout 5% - 60% Periods in which payout is expected to occur 2016 - 2017 Discount rate 4.25% September 30, 2014 Unobservable Input Range Warrant liability and Series 1 nonconvertible preferred stock Probabilities of payout 10% - 90% Periods in which payout is expected to occur 2015 - 2016 Discount rate 4.25%
Rollforward of Aggregate Fair Values of Warrants	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: Balance, September 30, 2012 $ 2,001 Decrease in fair value (381 ) Balance, September 30, 2013 1,620 Warrants exercised (206 ) Series 1 nonconvertible preferred stock issued 206 Increase in fair value 166 Balance, September 30, 2014 1,786 Decrease in fair value (347 ) Balance, September 30, 2015 $ 1,439

Marketable Securities (Tables)

Marketable Securities (Tables)	12 Months Ended
	Sep. 30, 2015
Investments, Debt and Equity Securities [Abstract]
Fair Value of Available-for-Sale Marketable Securities by Type of Security	As of September 30, 2015 and 2014, the fair value of available-for-sale marketable securities by type of security was as follows: September 30, 2015 Amortized Cost Gross Unrealized Gross Unrealized Fair Value Corporate bonds $ 151,012 $ 77 $ (69 ) $ 151,020 U.S. Agency bonds 36,652 45 — 36,697 $ 187,664 $ 122 $ (69 ) $ 187,717 September 30, 2014 Amortized Cost Gross Unrealized Gross Unrealized Fair Value Commercial paper $ 7,499 $ — $ — $ 7,499 Corporate bonds 88,156 14 (114 ) 88,056 U.S. Agency bonds 5,513 — — 5,513 $ 101,168 $ 14 $ (114 ) $ 101,068

Property and Equipment (Tables)

Property and Equipment (Tables)	12 Months Ended
	Sep. 30, 2015
Property, Plant and Equipment [Abstract]
Schedule of Property and Equipment	Property and equipment consisted of the following as of September 30, 2015 and 2014: September 30, 2015 2014 Laboratory and office equipment $ 5,907 $ 4,829 Leasehold improvements 1,290 300 Purchased software 443 414 Computer equipment 137 111 Furniture 496 284 Construction in progress 1,889 — 10,162 5,938 Less: Accumulated depreciation and amortization (4,276 ) (4,135 ) $ 5,886 $ 1,803

Accrued Expenses, Other Curre29

Accrued Expenses, Other Current Liabilities and Other Long-Term Liabilities (Tables)	12 Months Ended
	Sep. 30, 2015
Payables and Accruals [Abstract]
Accrued Expenses, Other Current Liabilities and Other Long-Term Liabilities	Accrued expenses, other current liabilities and other long-term liabilities consisted of the following as of September 30, 2015 and 2014: September 30, 2015 2014 Accrued expenses and other current liabilities: Accrued payroll and related expenses $ 1,622 $ 1,275 Accrued fixed asset purchases 1,307 — Accrued professional fees 338 436 Accrued preclinical and clinical expenses 237 493 Capital lease obligation 69 — Accrued vendor manufacturing 18 116 Accrued third-party license fee — 240 Accrued other 371 312 $ 3,962 $ 2,872 Other long-term liabilities: Accrued rent expense $ 628 $ 153 Capital lease obligation 529 — Uncertain tax positions 448 — Asset retirement obligation 108 76 $ 1,713 $ 229

Series 1 Nonconvertible Prefe30

Series 1 Nonconvertible Preferred Stock (Tables)	12 Months Ended
	Sep. 30, 2015
Text Block [Abstract]
Summary of Warrant Activity	The following table summarizes the Company’s warrant activity since October 1, 2012: Series 1 Weighted Outstanding, as of September 30, 2012 1,999,989 $ 0.01 Granted — Expired — Exercised — Outstanding, as of September 30, 2013 1,999,989 $ 0.01 Granted — Expired — Exercised (225,408 ) Outstanding, as of September 30, 2014 1,774,581 $ 0.01 Granted — Expired — Exercised — Outstanding, as of September 30, 2015 1,774,581 $ 0.01

Stock-Based Awards (Tables)

Stock-Based Awards (Tables)	12 Months Ended
	Sep. 30, 2015
Data Used to Determine Value of Stock Option Grants, Presented on Weighted Average Basis	The relevant data used to determine the value of the stock option grants is as follows, presented on a weighted average basis: Years Ended September 30, 2015 2014 2013 Risk-free interest rate 1.85 % 1.89 % 1.05 % Expected term (in years) 6.03 6.06 6.09 Expected volatility 74 % 75 % 73 % Expected dividend yield 0 % 0 % 0 %
Stock Option Activity	The following table summarizes stock option activity for the year ended September 30, 2015: Shares Weighted Weighted Aggregate Outstanding as of September 30, 2014 1,389,437 $ 15.39 7.2 $ 33,573 Granted 526,755 42.36 Exercised (122,260 ) 5.94 Forfeited (41,922 ) 32.24 Outstanding as of September 30, 2015 1,752,010 $ 23.76 7.2 $ 25,093 Options vested and expected to vest as of September 30, 2015 1,576,413 $ 24.71 7.1 $ 21,369 Options exercisable as of September 30, 2015 854,183 $ 14.58 5.7 $ 18,852
Stock-Based Compensation Expense	The Company recorded stock-based compensation expense for the years ended September 30, 2015, 2014 and 2013 in the following expense categories: Years Ended September 30, 2015 2014 2013 Research and development $ 1,644 $ 762 $ 393 General and administrative 4,194 1,920 670 $ 5,838 $ 2,682 $ 1,063
Relative Net Shareholder Return Units rTSRU [Member]
Data Used to Determine Value of Stock Option Grants, Presented on Weighted Average Basis	The table below sets forth the assumptions used to value the awards and the estimated grant-date fair value: Risk-free interest rate 0.61 % Dividend yield 0 % Expected volatility 55.66 % Remaining performance period (years) 1.86 Estimated fair value per share of rTSRUs granted $ 26.51

Net Income (Loss) Per Share (Ta

Net Income (Loss) Per Share (Tables)	12 Months Ended
	Sep. 30, 2015
Earnings Per Share [Abstract]
Basic and Diluted Net Income Per Share Attributable to Common Stockholders	Basic and diluted net income (loss) per share attributable to common stockholders was calculated as follows for the years ended September 30, 2015, 2014 and 2013: Years Ended September 30, 2015 2014 2013 Basic net income (loss) per share attributable to common stockholders: Numerator: Net income $ 78,992 $ 34,438 $ 9,627 Accretion of redeemable convertible preferred stock to redemption value — — (2,526 ) Net income attributable to participating securities — — (13,670 ) Net income (loss) attributable to common stockholders $ 78,992 $ 34,438 $ (6,569 ) Denominator: Weighted average common shares outstanding—basic 18,673,484 18,354,791 9,788,039 Net income (loss) per share attributable to common stockholders—basic $ 4.23 $ 1.88 $ (0.67 ) Years Ended September 30, 2015 2014 2013 Diluted net income (loss) per share attributable to common stockholders: Numerator: Net income $ 78,992 $ 34,438 $ 9,627 Accretion of redeemable convertible preferred stock to redemption value — — (2,526 ) Net income attributable to participating securities — — (13,670 ) Net income (loss) attributable to common stockholders—diluted $ 78,992 $ 34,438 $ (6,569 ) Denominator: Weighted average common shares outstanding—basic 18,673,484 18,354,791 9,788,039 Dilutive effect of common stock equivalents 621,150 830,437 — Weighted average common shares outstanding—diluted 19,294,634 19,185,228 9,788,039 Net income (loss) per share attributable to common stockholders—diluted $ 4.09 $ 1.80 $ (0.67 )

Commitments and Contingencies (

Commitments and Contingencies (Tables)	12 Months Ended
	Sep. 30, 2015
Commitments and Contingencies Disclosure [Abstract]
Future Minimum Lease Payments	Future minimum lease payments as of September 30, 2015 are as follows: Years Ended September 30, Operating Capital Total 2016 $ 1,958 $ 68 $ 2,026 2017 2,010 73 2,083 2018 2,062 79 2,141 2019 2,117 85 2,202 2020 2,172 93 2,265 Thereafter 4,322 200 4,522 Total $ 14,641 $ 598 $ 15,239

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Sep. 30, 2015
Income Tax Disclosure [Abstract]
Summary of Provision or Benefit for Income Taxes	During the years ended September 30, 2015, 2014 and 2013, the Company recorded a provision or a benefit for income taxes as follows: Years Ended September 30, 2015 2014 2013 Current income tax expense: Federal $ 35,040 $ — $ — State 2,172 151 — Deferred income tax expense (benefit): Federal 7,371 (13,048 ) — State 1,880 (2,273 ) — $ 46,463 $ (15,170 ) $ —
Reconciliation of Income Tax Provision at Federal Statutory Income Tax Rate and Effective Tax Rate	A reconciliation of the U.S. federal statutory income tax rate to the Company’s effective income tax rate is as follows: Years Ended September 30, 2015 2014 2013 Federal statutory income tax rate 35.0 % 35.0 % 34.0 % State taxes, net of federal benefit 2.6 5.5 5.5 Federal research and development tax credit (0.1 ) (0.5 ) (2.5 ) Change in deferred tax asset valuation allowance — (118.8 ) (51.0 ) Change in statutory rate 0.3 (2.1 ) — Other (0.8 ) 2.2 14.0 Effective income tax rate 37.0 % (78.7 )% 0.0 %
Net Deferred Tax Assets and Liabilities	Net deferred tax assets as of September 30, 2015 and 2014 consisted of the following: September 30, 2015 2014 Net operating loss carryforwards $ — $ 2,952 Tax credit carryforwards — 5,920 Capitalized research and development expenses 2,903 4,756 Other temporary differences 3,204 1,693 Gross deferred tax assets 6,107 15,321 Valuation allowance — — Deferred tax assets $ 6,107 $ 15,321

Selected Quarterly Financial 35

Selected Quarterly Financial Data (unaudited) (Tables)	12 Months Ended
	Sep. 30, 2015
Quarterly Financial Information Disclosure [Abstract]
Schedule of Quarterly Financial Information	Quarterly financial information for fiscal 2015, 2014 and 2013 is presented in the following table, in thousands, except per share data: 2015 Quarter Ended December 31, 2014 March 31, 2015 June 30, 2015 September 30, 2015 Revenue $ 77,498 $ 57,367 $ 11,599 $ 14,416 Operating expenses 7,288 8,806 9,896 10,742 Other income, net 301 210 287 509 Income tax (expense) benefit (28,502 ) (20,018 ) 428 1,629 Net income 42,009 28,753 2,418 5,812 Net income per share attributable to common shareholders—basic $ 2.26 $ 1.54 $ 0.13 $ 0.30 Net income per share attributable to common shareholders—diluted $ 2.18 $ 1.49 $ 0.13 $ 0.29 2014 Quarter Ended December 31, 2013 March 31, 2014 June 30, 2014 September 30, 2014 Revenue $ 893 $ 2,160 $ 42,051 $ 2,637 Operating expenses 6,350 7,287 7,156 7,963 Other income (expense), net 87 (76 ) 36 236 Income tax benefit — — 15,122 48 Net income (loss) (5,370 ) (5,203 ) 50,053 (5,042 ) Net income (loss) per share attributable to common shareholders—basic $ (0.30 ) $ (0.28 ) $ 2.70 $ (0.27 ) Net income (loss) per share attributable to common shareholders—diluted $ (0.30 ) $ (0.28 ) $ 2.61 $ (0.27 )

Summary of Significant Accoun36

Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($)	12 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2013
Summary of Accounting and Financial Policies [Line Items]
Adjustment to fair value	$ 0	$ 0	$ 0
Cash and investment restricted as a collateral for outstanding letter of credit	608,000	436,000
Money Market Funds [Member]
Summary of Accounting and Financial Policies [Line Items]
Cash and investment restricted as a collateral for outstanding letter of credit	$ 608,000	$ 436,000
Maximum [Member]
Summary of Accounting and Financial Policies [Line Items]
Short-term investments maturity period	Ninety days
Short-term marketable securities maturity period	1 year
Minimum [Member]
Summary of Accounting and Financial Policies [Line Items]
Short-term marketable securities maturity period	90 days
Long-term marketable securities maturity period	One year
Income tax benefit recognition, percentage of likelihood of being realized upon settlement	50.00%

Summary of Significant Accoun37

Summary of Significant Accounting Policies - Property and Equipment Estimated Useful Lives (Detail)	12 Months Ended
	Sep. 30, 2015
Laboratory and Office Equipment [Member]
Property, Plant and Equipment [Line Items]
Property plant and equipment useful life	5 years
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Leasehold improvements useful life	Shorter of life of lease or estimated useful life
Purchased Software [Member]
Property, Plant and Equipment [Line Items]
Property plant and equipment useful life	3 years
Computer Equipment [Member]
Property, Plant and Equipment [Line Items]
Property plant and equipment useful life	3 years
Furniture [Member]
Property, Plant and Equipment [Line Items]
Property plant and equipment useful life	7 years

Fair Value of Financial Asset38

Fair Value of Financial Assets and Liabilities - Financial Assets and Liabilities that were Subject to Fair Value Measurement on Recurring Basis (Detail) - USD ($) $ in Thousands	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2012	Nov. 30, 2010
Assets:
Cash equivalents	$ 21,327	$ 30,239
Available for sale securities, fair value	187,717	101,068
Assets, Fair Value Disclosure, Total	209,044	131,307
Liabilities:
Liabilities	1,439	1,786	$ 1,620	$ 2,001
Liabilities, Fair Value Disclosure, Total	1,439	1,786
Commercial Paper [Member]
Assets:
Available for sale securities, fair value		7,499
Corporate Bonds [Member]
Assets:
Available for sale securities, fair value	151,020	88,056
U.S. Agency Bonds [Member]
Assets:
Available for sale securities, fair value	36,697	5,513
Warrant Liability [Member]
Liabilities:
Liabilities	1,276	1,584
Series 1 Nonconvertible Preferred Stock [Member]
Liabilities:
Liabilities	163	202
Series 1 Nonconvertible Preferred Stock [Member] | Warrant Liability [Member]
Liabilities:
Liabilities	1,276	1,584			$ 1,280
Level 1 [Member]
Assets:
Cash equivalents	21,327	30,239
Assets, Fair Value Disclosure, Total	21,327	30,239
Level 2 [Member]
Assets:
Assets, Fair Value Disclosure, Total	187,717	101,068
Level 2 [Member] | Commercial Paper [Member]
Assets:
Available for sale securities, fair value		7,499
Level 2 [Member] | Corporate Bonds [Member]
Assets:
Available for sale securities, fair value	151,020	88,056
Level 2 [Member] | U.S. Agency Bonds [Member]
Assets:
Available for sale securities, fair value	36,697	5,513
Level 3 [Member]
Liabilities:
Liabilities, Fair Value Disclosure, Total	1,439	1,786
Level 3 [Member] | Warrant Liability [Member]
Liabilities:
Liabilities	1,276	1,584
Level 3 [Member] | Series 1 Nonconvertible Preferred Stock [Member]
Liabilities:
Liabilities	$ 163	$ 202

Fair Value of Financial Asset39

Fair Value of Financial Assets and Liabilities - Additional Information (Detail) - USD ($)	12 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2012	Nov. 30, 2010
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Transfers between Level 1, Level 2 and Level 3	$ 0	$ 0	$ 0
Fair value of Series 1 nonconvertible preferred stock	1,439,000	1,786,000	$ 1,620,000	$ 2,001,000
Series 1 Nonconvertible Preferred Stock [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of Series 1 nonconvertible preferred stock	163,000	202,000
Warrant Liability [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of Series 1 nonconvertible preferred stock	1,276,000	1,584,000
Warrant Liability [Member] | Series 1 Nonconvertible Preferred Stock [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of Series 1 nonconvertible preferred stock	$ 1,276,000	$ 1,584,000			$ 1,280,000

Fair Value of Financial Asset40

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]	12 Months Ended
	Sep. 30, 2015	Sep. 30, 2014
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Periods in which payout is expected to occur, beginning	2,016	2,015
Periods in which payout is expected to occur, ending	2,017	2,016
Discount rate	4.25%	4.25%
Minimum [Member]
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Probabilities of payout	5.00%	10.00%
Maximum [Member]
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Probabilities of payout	60.00%	90.00%

Fair Value of Financial Asset41

Fair Value of Financial Assets and Liabilities - Rollforward of Aggregate Fair Values of Warrants (Detail) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2013
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning Balance	$ 1,786	$ 1,620	$ 2,001
Decrease in fair value	(347)		(381)
Increase in fair value		166
Ending Balance	1,439	1,786	$ 1,620
Series 1 Nonconvertible Preferred Stock [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning Balance	202
Series 1 nonconvertible preferred stock issued		206
Ending Balance	163	202
Warrant Liability [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning Balance	1,584
Warrants exercised		(206)
Ending Balance	1,276	1,584
Warrant Liability [Member] | Series 1 Nonconvertible Preferred Stock [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Beginning Balance	1,584
Ending Balance	$ 1,276	$ 1,584

Marketable Securities - Fair Va

Marketable Securities - Fair Value of Available-for-Sale Marketable Securities by Type of Security (Detail) - USD ($) $ in Thousands	Sep. 30, 2015	Sep. 30, 2014
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 187,664	$ 101,168
Gross Unrealized Gains	122	14
Gross Unrealized Losses	(69)	(114)
Fair Value	187,717	101,068
Commercial Paper [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		7,499
Fair Value		7,499
Corporate Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	151,012	88,156
Gross Unrealized Gains	77	14
Gross Unrealized Losses	(69)	(114)
Fair Value	151,020	88,056
U.S. Agency Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	36,652	5,513
Gross Unrealized Gains	45
Fair Value	$ 36,697	$ 5,513

Marketable Securities - Additio

Marketable Securities - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2015	Sep. 30, 2014
Schedule of Available-for-sale Securities [Line Items]
Marketable securities maturing in greater than one year, aggregate fair value	$ 64,238	$ 41,003
Short Term Marketable Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Maturity period of the marketable securities	Within one year
Corporate Bond Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Maturity period of the marketable securities	Between one and three years
U.S. Agency Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Maturity period of the marketable securities	Between one and three years

Property and Equipment - Schedu

Property and Equipment - Schedule of Property and Equipment (Detail) - USD ($) $ in Thousands	Sep. 30, 2015	Sep. 30, 2014
Property, Plant and Equipment [Line Items]
Property and equipment	$ 10,162	$ 5,938
Less: Accumulated depreciation and amortization	(4,276)	(4,135)
Property and equipment, net	5,886	1,803
Laboratory and Office Equipment [Member]
Property, Plant and Equipment [Line Items]
Property and equipment	5,907	4,829
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Property and equipment	1,290	300
Purchased Software [Member]
Property, Plant and Equipment [Line Items]
Property and equipment	443	414
Computer Equipment [Member]
Property, Plant and Equipment [Line Items]
Property and equipment	137	111
Furniture [Member]
Property, Plant and Equipment [Line Items]
Property and equipment	496	$ 284
Construction in Progress [Member]
Property, Plant and Equipment [Line Items]
Property and equipment	$ 1,889

Property and Equipment - Additi

Property and Equipment - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2013
Property, Plant and Equipment [Abstract]
Depreciation and amortization expense	$ 639	$ 352	$ 221
Cost of assets sold	518	554	420
Gain of assets sold	$ 31	$ 3	$ 100

Accrued Expenses, Other Curre46

Accrued Expenses, Other Current Liabilities and Other Long-Term Liabilities - Accrued Expenses Other Current Liabilities and Other Long-Term Liabilities (Detail) - USD ($) $ in Thousands	Sep. 30, 2015	Sep. 30, 2014
Accrued expenses and other current liabilities:
Accrued payroll and related expenses	$ 1,622	$ 1,275
Accrued fixed asset purchases	1,307
Accrued professional fees	338	436
Accrued preclinical and clinical expenses	237	493
Capital lease obligation	69
Accrued vendor manufacturing	18	116
Accrued third-party license fee		240
Accrued other	371	312
Accrued expenses	3,962	2,872
Other long-term liabilities:
Accrued rent expense	628	153
Capital lease obligation	529
Uncertain tax positions	448
Asset retirement obligation	108	76
Other long-term liabilities	$ 1,713	$ 229

Accrued Expenses, Other Curre47

Accrued Expenses, Other Current Liabilities and Other Long-Term Liabilities - Additional Information (Detail) $ in Thousands	Sep. 30, 2015USD ($)
Other Liabilities Disclosure [Abstract]
Capital lease obligations	$ 598

Collaboration Agreements - Addi

Collaboration Agreements - Additional Information (Detail) - USD ($)	12 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2012
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Milestone revenue payments received	$ 125,000,000	$ 40,000,000	$ 26,000,000
Revenue invoiced but unpaid	15,289,000	1,724,000
Revenue unpaid and included in unbilled receivables	$ 433,000	2,770,000
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 net sales
Agreement continuation period	10 years
Novartis [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Milestone revenue payments received			12,675,000
Upfront license fee received				$ 34,442,000,000
Amount attributable to license fees			10,894,000
Amount attributable to the performance of research service			1,781,000
National Institutes of Health, National Institute of Allergy and Infectious Diseases Contract [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaboration agreement date	Sep. 30, 2011
Funding received for research and development	$ 18,672,000
Revenue from grants	1,803,000	7,741,000	4,378,000
Revenue invoiced but unpaid	955,000	1,724,000
Revenue unpaid and included in unbilled receivables	433,000	2,770,000
Milestone Payments [Member] | AbbVie [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Milestone revenue payments received	125,000,000	40,000,000	$ 15,000,000
Proceed received to fund research activities and preferred stock financing	319,000,000
Additional Funding Agreement Terms [Member] | AbbVie [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Expected proceed from milestone payment	80,000,000
JAPAN | AbbVie [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Expected proceed from milestone payment	$ 30,000,000
Paritaprevir 3-DAA Regimen [Member] | AbbVie [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Percentage of net sales to be allocated	30.00%
Paritaprevir 2-DAA Regimen [Member] | AbbVie [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Percentage of net sales to be allocated	45.00%
Abt 493 2-DAA Regimen [Member] | AbbVie [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Percentage of net sales to be allocated	50.00%
Abt 493 3-DAA Regimen [Member] | AbbVie [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Percentage of net sales to be allocated	33.33%
Abbott Laboratories [Member] | AbbVie [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaboration agreement date	Nov. 27, 2006
Amendment To Novartis Agreement [Member] | Novartis [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Future milestone payments		$ 0

Stockholders' Equity - Addition

Stockholders' Equity - Additional Information (Detail) $ / shares in Units, $ in Thousands	Mar. 26, 2013USD ($)$ / sharesshares	Mar. 01, 2013	Sep. 30, 2015shares	Sep. 30, 2013USD ($)shares	Sep. 30, 2014shares	Mar. 31, 2013shares	Feb. 29, 2012shares
Class of Stock [Line Items]
Common stock, shares authorized			100,000,000		100,000,000	100,000,000	70,000,000
Reverse stock split ratio		4.31
Shares issued in initial public offering	4,600,000
Proceeds from initial public offering, net of underwriting discounts and commissions | $	$ 59,892			$ 59,892
Shares issued, price per share | $ / shares	$ 14
Common Stock [Member]
Class of Stock [Line Items]
Shares issued in initial public offering				4,600,000
Treasury stock, shares retired but unissued			(208,816)
Conversion of Redeemable Convertible Preferred Stock and Convertible Preferred Stock [Member]
Class of Stock [Line Items]
Shares of common stock issued upon conversion of preferred stock	11,656,875

Series 1 Nonconvertible Prefe50

Series 1 Nonconvertible Preferred Stock - Additional Information (Detail) - USD ($)	Feb. 05, 2014	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2012	Nov. 30, 2010
Class of Stock [Line Items]
Fair value of series 1 nonconvertible preferred stock warrants		$ 1,439,000	$ 1,786,000	$ 1,620,000	$ 2,001,000
Warrant Liability [Member]
Class of Stock [Line Items]
Fair value of series 1 nonconvertible preferred stock warrants		$ 1,276,000	1,584,000
Series 1 Nonconvertible Preferred Stock [Member]
Class of Stock [Line Items]
Preferred Shares authorized		1,999,989
Par value of outstanding convertible preferred stock		$ 0.01
Per share value adjusted for stock dividend		1
Preferred stock redemption price per share		$ 1
Redemption period		60 days
Number of shares issuable upon exercise of the warrants						1,999,989
Warrant expiration date		Oct. 4, 2017
Transfer of assets upon exercise of warrants maximum amount						$ 2,000,000
Fair value of series 1 nonconvertible preferred stock warrants		$ 163,000	202,000
Change in fair value of warrants		(347,000)	166,000	$ (361,000)
Warrant exercised	225,408
Warrants issuance	223,153
Fair value of the Series 1 nonconvertible preferred stock		163,000	202,000
Aggregate liquidation preference			2,000,000
Series 1 Nonconvertible Preferred Stock [Member] | Warrant Liability [Member]
Class of Stock [Line Items]
Fair value of series 1 nonconvertible preferred stock warrants		$ 1,276,000	$ 1,584,000			$ 1,280,000

Series 1 Nonconvertible Prefe51

Series 1 Nonconvertible Preferred Stock - Summary of Warrant Activity (Detail) - Series 1 Nonconvertible Preferred Stock [Member] - $ / shares	12 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2013
Preferred Stock And Warrant [Line Items]
Beginning Balance	1,774,581	1,999,989	1,999,989
Granted	0	0	0
Expired	0	0	0
Exercised		(225,408)
Ending Balance	1,774,581	1,774,581	1,999,989
Weighted Average Exercise Price Outstanding, Beginning Balance	$ 0.01	$ 0.01	$ 0.01
Weighted Average Exercise Price Outstanding, Ending Balance	$ 0.01	$ 0.01	$ 0.01

Stock-Based Awards - Additional

Stock-Based Awards - Additional Information (Detail) - USD ($)	Sep. 30, 2015	Oct. 01, 2014	Mar. 31, 2013	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock reserved	185,614			185,614
Shares issued under the ESPP	0
Period for service based award				4 years
Options granted to executives				526,755
Aggregate intrinsic value of stock options exercised				$ 4,827,000	$ 3,219,000	$ 7,574,000
Cash proceeds from exercise of stock options				$ 726,000	$ 1,054,000	$ 559,000
Weighted average grant date fair value of option granted				$ 27.77	$ 19.98	$ 9.16
Aggregate of unrecognized stock-based compensation cost	$ 18,399,000			$ 18,399,000
Weighted average recognition period				2 years 9 months 18 days
2012 Equity Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock shares authorized		557,863
Percentage of potential common stock shares to be issued				3.00%
Shares available for future grant	444,173			444,173
Options granted, vesting period				4 years
Options granted, expiration period				10 years
2012 Equity Incentive Plan [Member] | Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock shares authorized				2,088,167
Performance Share Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options granted to executives				20,900
Compensation expenses				$ 0
Performance Share Units [Member] | Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares range percentage				0.00%
Fair value of performance shares units	$ 0			$ 0
Performance Share Units [Member] | Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares range percentage				200.00%
Fair value of performance shares units	$ 1,501			$ 1,501
Relative Net Shareholder Return Units rTSRU [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options granted to executives				20,900
Fair value of options at the grant date				$ 554,000
Compensation expenses				$ 181,000
Relative Net Shareholder Return Units rTSRU [Member] | Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares range percentage				0.00%
Relative Net Shareholder Return Units rTSRU [Member] | Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares range percentage				200.00%
Executive Officer [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options granted to executives			167,052	41,800
Fair value of options at the grant date			$ 2,479,000
Compensation expenses				$ 0	$ 206,000	$ 0
Executive Officer [Member] | 2012 Equity Incentive Plan [Member] | Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options granted, vesting period				1 year
Executive Officer [Member] | 2012 Equity Incentive Plan [Member] | Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options granted, vesting period				4 years
Board of Directors [Member] | 2012 Equity Incentive Plan [Member] | Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options granted, vesting period				2 years
Board of Directors [Member] | 2012 Equity Incentive Plan [Member] | Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options granted, vesting period				3 years

Stock-Based Awards - Data Used

Stock-Based Awards - Data Used to Determine Value of Stock Option Grants, Presented on Weighted Average Basis (Detail)	12 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2013
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Risk-free interest rate	1.85%	1.89%	1.05%
Expected term (in years)	6 years 11 days	6 years 22 days	6 years 1 month 2 days
Expected volatility	74.00%	75.00%	73.00%
Expected dividend yield	0.00%	0.00%	0.00%

Stock-Based Awards - Stock Opti

Stock-Based Awards - Stock Option Activity (Detail) - USD ($) $ / shares in Units, $ in Thousands	Sep. 30, 2014	Sep. 30, 2015
Shares Issuable Under Options
Outstanding as of beginning of period		1,389,437
Granted		526,755
Exercised		(122,260)
Forfeited		(41,922)
Outstanding as of end of period	1,389,437	1,752,010
Options vested and expected to vest as of end of period		1,576,413
Options exercisable as of end of period		854,183
Weighted Average Exercise Price
Outstanding as of beginning of period		$ 15.39
Granted		42.36
Exercised		5.94
Forfeited		32.24
Outstanding as of ending balance	$ 15.39	23.76
Options vested and expected to vest as of end of period		24.71
Options exercisable as of end of period		$ 14.58
Weighted Average Remaining Contractual Term (In years)
Outstanding as of end of period	7 years 2 months 12 days	7 years 2 months 12 days
Options vested and expected to vest as of end period		7 years 1 month 6 days
Options exercisable as of end of period		5 years 8 months 12 days
Aggregate Intrinsic Value
Outstanding as of beginning of period		$ 33,573
Outstanding as of end of period	$ 33,573	25,093
Options vested and expected to vest as of end of period		21,369
Options exercisable as of end of period		$ 18,852

Stock-Based Awards - Stock-Base

Stock-Based Awards - Stock-Based Compensation Expense (Detail) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2013
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	$ 5,838	$ 2,682	$ 1,063
Research and Development [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	1,644	762	393
General and Administrative [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	$ 4,194	$ 1,920	$ 670

Stock-Based Awards - Weighted A

Stock-Based Awards - Weighted Average Assumptions Used To Value Awards and Estimated Grant Date Fair Value (Detail) - $ / shares	12 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Risk-free interest rate	1.85%	1.89%	1.05%
Dividend yield	0.00%	0.00%	0.00%
Expected volatility	74.00%	75.00%	73.00%
Remaining performance period (years)	6 years 11 days	6 years 22 days	6 years 1 month 2 days
Relative Net Shareholder Return Units rTSRU [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Risk-free interest rate	0.61%
Dividend yield	0.00%
Expected volatility	55.66%
Remaining performance period (years)	1 year 10 months 10 days
Estimated fair value per share of rTSRUs granted	$ 26.51

Net Income (Loss) Per Share - B

Net Income (Loss) Per Share - Basic and Diluted Net Income Per Share Attributable to Common Stockholders (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2013
Basic net income (loss) per share attributable to common stockholders:
Net income	$ 5,812	$ 2,418	$ 28,753	$ 42,009	$ (5,042)	$ 50,053	$ (5,203)	$ (5,370)	$ 78,992	$ 34,438	$ 9,627
Accretion of redeemable convertible preferred stock to redemption value											(2,526)
Net income attributable to participating securities											(13,670)
Net income (loss) attributable to common stockholders									$ 78,992	$ 34,438	$ (6,569)
Weighted average common shares outstanding-basic									18,673,484	18,354,791	9,788,039
Net income (loss) per share attributable to common stockholders-basic	$ 0.30	$ 0.13	$ 1.54	$ 2.26	$ (0.27)	$ 2.70	$ (0.28)	$ (0.30)	$ 4.23	$ 1.88	$ (0.67)
Diluted net income (loss) per share attributable to common stockholders:
Net income	$ 5,812	$ 2,418	$ 28,753	$ 42,009	$ (5,042)	$ 50,053	$ (5,203)	$ (5,370)	$ 78,992	$ 34,438	$ 9,627
Accretion of redeemable convertible preferred stock to redemption value											(2,526)
Net income attributable to participating securities											(13,670)
Net income (loss) attributable to common stockholders-diluted									$ 78,992	$ 34,438	$ (6,569)
Weighted average common shares outstanding-basic									18,673,484	18,354,791	9,788,039
Dilutive effect of common stock equivalents									621,150	830,437
Weighted average common shares outstanding-diluted									19,294,634	19,185,228	9,788,039
Net income (loss) per share attributable to common stockholders-diluted	$ 0.29	$ 0.13	$ 1.49	$ 2.18	$ (0.27)	$ 2.61	$ (0.28)	$ (0.30)	$ 4.09	$ 1.80	$ (0.67)

Net Income (Loss) Per Share - A

Net Income (Loss) Per Share - Additional Information (Detail) - shares	12 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2013
Stock Options and Awards [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Shares excluded from the computation of diluted net income per share	604,632	330,430	1,713,313

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Detail) - USD ($)	12 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2013	Oct. 01, 2012
Commitments And Contingencies [Line Items]
Rent expense	$ 1,326,000	$ 948,000	$ 948,000
Office lease expiration period	September 2,022
Outstanding letter of credit	$ 608,000	436,000
Restricted cash	608,000	436,000
Tenant improvement allowance	598,000
Upfront license fees payable	350,000
License expense	200,000	250,000	250,000
Maintenance fees	105,000
One-time fee	50,000
License agreement, recorded liability	9,856,000	6,761,000
License agreement, recorded liability paid	1,543,000	1,874,000
Company's obligation to pay	5,000,000
Payment for license agreement	500,000
License Agreement Terms [Member]
Commitments And Contingencies [Line Items]
License agreement, recorded liability				$ 995,000
License agreement, recorded liability paid	$ 200,000	$ 250,000	$ 350,000

Commitments and Contingencies60

Commitments and Contingencies - Future Minimum Lease Payments (Detail) $ in Thousands	Sep. 30, 2015USD ($)
Commitments and Contingencies Disclosure [Abstract]
2,016	$ 1,958
2,017	2,010
2,018	2,062
2,019	2,117
2,020	2,172
Thereafter	4,322
Total	14,641
2,016	68
2,017	73
2,018	79
2,019	85
2,020	93
Thereafter	200
Total	598
2,016	2,026
2,017	2,083
2,018	2,141
2,019	2,202
2,020	2,265
Thereafter	4,522
Total	$ 15,239

Income Taxes - Summary of Provi

Income Taxes - Summary of Provision or Benefit for Income Taxes (Detail) - USD ($)	3 Months Ended						12 Months Ended
	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2013
Current income tax expense:
Federal							$ 35,040,000
State							2,172,000	$ 151,000
Deferred income tax expense (benefit):
Federal							7,371,000	(13,048,000)
State							1,880,000	(2,273,000)
Total tax expense	$ 1,629,000	$ 428,000	$ (20,018,000)	$ (28,502,000)	$ 48,000	$ 15,122,000	$ 46,463,000	$ (15,170,000)	$ 0

Income Taxes - Additional Infor

Income Taxes - Additional Information (Detail) - USD ($)	3 Months Ended						12 Months Ended
	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2013
Income Tax [Line Items]
Income tax expense (benefit)	$ 1,629,000	$ 428,000	$ (20,018,000)	$ (28,502,000)	$ 48,000	$ 15,122,000	$ 46,463,000	$ (15,170,000)	$ 0
Income before income taxes							$ 125,455,000	19,268,000	$ 9,627,000
Decreases recorded as benefit to income tax provision								$ 22,892,000
Effective income tax rate							37.00%	(78.70%)	0.00%
Federal statutory income tax rate							35.00%	35.00%	34.00%
Unrecognized tax benefit	$ 448,000				0		$ 448,000	$ 0
Federal [Member]
Income Tax [Line Items]
Net operating loss carryforwards					0			0
Research and development tax credit carryforwards					4,481,000			4,481,000
State [Member]
Income Tax [Line Items]
Net operating loss carryforwards					8,433,000			8,433,000
Research and development tax credit carryforwards					$ 2,214,000			$ 2,214,000

Income Taxes - Reconciliation o

Income Taxes - Reconciliation of Income Tax Provision at Federal Statutory Income Tax Rate and Effective Tax Rate (Detail)	12 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2013
Income Tax Disclosure [Abstract]
Federal statutory income tax rate	35.00%	35.00%	34.00%
State taxes, net of federal benefit	2.60%	5.50%	5.50%
Federal research and development tax credit	(0.10%)	(0.50%)	(2.50%)
Change in deferred tax asset valuation allowance		(118.80%)	(51.00%)
Change in statutory rate	0.30%	(2.10%)
Other	(0.80%)	2.20%	14.00%
Effective income tax rate	37.00%	(78.70%)	0.00%

Income Taxes - Net Deferred Tax

Income Taxes - Net Deferred Tax Assets and Liabilities (Detail) - USD ($) $ in Thousands	Sep. 30, 2015	Sep. 30, 2014
Income Tax Disclosure [Abstract]
Net operating loss carryforwards		$ 2,952
Tax credit carryforwards		5,920
Capitalized research and development expenses	$ 2,903	4,756
Other temporary differences	3,204	1,693
Gross deferred tax assets	6,107	15,321
Valuation allowance	0	0
Deferred tax assets	$ 6,107	$ 15,321

401(k) Plan - Additional Inform

401(k) Plan - Additional Information (Detail) - USD ($)	12 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2013
Defined Benefit Plan Disclosure [Line Items]
Annual base salary of employee		$ 8,000
Benefits charged to operating expenses	$ 382,000	180,000	$ 90,000
Scenario, Previously Reported [Member]
Defined Benefit Plan Disclosure [Line Items]
Annual base salary of employee		$ 4,000
Maximum [Member]
Defined Benefit Plan Disclosure [Line Items]
Percentage of annual contribution		3.00%
Maximum [Member] | Scenario, Previously Reported [Member]
Defined Benefit Plan Disclosure [Line Items]
Percentage of annual contribution		2.00%

Selected Quarterly Financial 66

Selected Quarterly Financial Data (unaudited) - Schedule of Quarterly Financial Information (Detail) - USD ($)	3 Months Ended								12 Months Ended
	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2013
Quarterly Financial Information Disclosure [Abstract]
Revenue	$ 14,416,000	$ 11,599,000	$ 57,367,000	$ 77,498,000	$ 2,637,000	$ 42,051,000	$ 2,160,000	$ 893,000	$ 160,880,000	$ 47,741,000	$ 32,053,000
Operating expenses	10,742,000	9,896,000	8,806,000	7,288,000	7,963,000	7,156,000	7,287,000	6,350,000	36,732,000	28,756,000	23,024,000
Other income (expense), net	509,000	287,000	210,000	301,000	236,000	36,000	(76,000)	87,000
Income tax (expense) benefit	1,629,000	428,000	(20,018,000)	(28,502,000)	48,000	15,122,000			46,463,000	(15,170,000)	0
Net income (loss)	$ 5,812,000	$ 2,418,000	$ 28,753,000	$ 42,009,000	$ (5,042,000)	$ 50,053,000	$ (5,203,000)	$ (5,370,000)	$ 78,992,000	$ 34,438,000	$ 9,627,000
Net income (loss) per share attributable to common shareholders-basic	$ 0.30	$ 0.13	$ 1.54	$ 2.26	$ (0.27)	$ 2.70	$ (0.28)	$ (0.30)	$ 4.23	$ 1.88	$ (0.67)
Net income (loss) per share attributable to common shareholders-diluted	$ 0.29	$ 0.13	$ 1.49	$ 2.18	$ (0.27)	$ 2.61	$ (0.28)	$ (0.30)	$ 4.09	$ 1.80	$ (0.67)