Enanta Pharmaceuticals (ENTA) 10-K 11 Dec 14 2014 FY Annual report Financial data

Document_and_Entity_Informatio

Document and Entity Information (USD $)	12 Months Ended
	Sep. 30, 2014	Dec. 01, 2014	Mar. 31, 2014
Document And Entity Information [Abstract]	'	'	'
Document Type	'10-K	'	'
Amendment Flag	'false	'	'
Document Period End Date	30-Sep-14	'	'
Document Fiscal Year Focus	'2014	'	'
Document Fiscal Period Focus	'FY	'	'
Trading Symbol	'ENTA	'	'
Entity Registrant Name	'ENANTA PHARMACEUTICALS INC	'	'
Entity Central Index Key	'0001177648	'	'
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	'	18,604,085	'
Entity Public Float	'	'	$601,630,755

Consolidated_Balance_Sheets

Consolidated Balance Sheets (USD $)	Sep. 30, 2014	Sep. 30, 2013
In Thousands, unless otherwise specified
Current assets:	'	'
Cash and cash equivalents	$30,699	$8,859
Short-term marketable securities	60,065	92,621
Accounts receivable	1,724	808
Unbilled receivables	2,770	784
Deferred tax assets	11,123	'
Prepaid expenses and other current assets	1,594	1,641
Total current assets	107,975	104,713
Property and equipment, net	1,803	1,121
Long-term marketable securities	41,003	10,703
Deferred tax assets	4,198	'
Restricted cash	436	436
Total assets	155,415	116,973
Current liabilities:	'	'
Accounts payable	1,874	1,481
Accrued expenses	2,872	3,035
Deferred revenue	'	10
Total current liabilities	4,746	4,526
Warrant liability	1,584	1,620
Other long-term liabilities	229	359
Total liabilities	6,761	6,505
Commitments and contingencies (Note 12)	'	'
Stockholders' equity:	'	'
Common stock; $0.01 par value; 100,000,000 shares authorized; 18,803,390 and 18,138,597 shares issued and 18,594,574 and 17,929,781 shares outstanding at September 30, 2014 and 2013, respectively	188	181
Additional paid-in capital	221,580	217,741
Treasury stock, at par value; 208,816 shares at September 30, 2014 and 2013	-2	-2
Accumulated other comprehensive loss	-100	-2
Accumulated deficit	-73,012	-107,450
Total stockholders' equity	148,654	110,468
Total liabilities and stockholders' equity	155,415	116,973
Series 1 Nonconvertible Preferred Stock [Member]	'	'
Current liabilities:	'	'
Series 1 nonconvertible preferred stock	$202	'

Consolidated_Balance_Sheets_Pa

Consolidated Balance Sheets (Parenthetical) (USD $)	Sep. 30, 2014	Sep. 30, 2013
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	18,803,390	18,138,597
Common stock, shares outstanding	18,594,574	17,929,781
Treasury stock, shares	208,816	208,816

Consolidated_Statements_of_Ope

Consolidated Statements of Operations (USD $)	12 Months Ended
In Thousands, except Share data, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2012
Income Statement [Abstract]	'	'	'
Revenue	$47,741	$32,053	$41,706
Operating expenses:	'	'	'
Research and development	18,740	16,841	15,115
General and administrative	10,016	6,183	5,302
Total operating expenses	28,756	23,024	20,417
Income from operations	18,985	9,029	21,289
Other income (expense):	'	'	'
Interest income	467	248	118
Interest expense	-18	-31	'
Change in fair value of warrant liability and Series 1 nonconvertible preferred stock, net	-166	381	-8
Total other income (expense), net	283	598	110
Income before income taxes	19,268	9,627	21,399
Income tax benefit	15,170	0	0
Net income	34,438	9,627	21,399
Accretion of redeemable convertible preferred stock to redemption value	'	-2,526	-5,367
Net income attributable to participating securities	'	-13,670	-14,663
Net income (loss) attributable to common stockholders	$34,438	($6,569)	$1,369
Net income (loss) per share attributable to common stockholders:	'	'	'
Basic	$1.88	($0.67)	$1.26
Diluted	$1.80	($0.67)	$1.13
Weighted average common shares outstanding:	'	'	'
Basic	18,354,791	9,788,039	1,088,784
Diluted	19,185,228	9,788,039	2,474,823

Consolidated_Statements_of_Com

Consolidated Statements of Comprehensive Income (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2012
Statement of Comprehensive Income [Abstract]	'	'	'
Net income	$34,438	$9,627	$21,399
Other comprehensive income (loss):	'	'	'
Net unrealized gains (losses) on marketable securities, net of tax of $0	-98	-12	11
Total other comprehensive income (loss)	-98	-12	11
Comprehensive income	$34,340	$9,615	$21,410

Consolidated_Statements_of_Com1

Consolidated Statements of Comprehensive Income (Parenthetical) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2012
Statement of Comprehensive Income [Abstract]	'	'	'
Net unrealized gains (losses) on marketable securities, tax	$0	$0	$0

Consolidated_Statements_of_Cha

Consolidated Statements of Changes in Redeemable and Convertible Preferred Stock and Stockholders' Equity (Deficit) (USD $)	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)	Accumulated Deficit [Member]
In Thousands, except Share data
Beginning Balance at Sep. 30, 2011	($131,961)	$153,588	$327	$12	'	($2)	($1)	($131,970)
Beginning Balance, Shares at Sep. 30, 2011	'	43,115,343	566,450	1,225,899	'	-208,816	'	'
Exercise of stock options	141	'	'	1	140	'	'	'
Exercise of stock options, Shares	'	'	'	117,248	'	'	'	'
Compensation expense related to stock options	424	'	'	'	424	'	'	'
Accretion of redeemable convertible preferred stock to redemption value	-5,367	5,367	'	'	-564	'	'	-4,803
Other comprehensive income (loss)	11	'	'	'	'	'	11	'
Net income	21,399	'	'	'	'	'	'	21,399
Ending Balance at Sep. 30, 2012	-115,353	158,955	327	13	'	-2	10	-115,374
Ending 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	'	'	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	'	'

Consolidated_Statements_of_Cas

Consolidated Statements of Cash Flows (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2012
Cash flows from operating activities	'	'	'
Net income	$34,438	$9,627	$21,399
Adjustments to reconcile net income to net cash provided by operating activities:	'	'	'
Depreciation and amortization expense	352	221	172
Non-cash interest expense	8	31	'
Change in fair value of warrant liability and Series 1 nonconvertible preferred stock	166	-381	8
Stock-based compensation expense	2,682	1,063	424
Gain on sale of marketable securities	-3	'	'
Gain on disposal of property and equipment	-3	-100	-63
Premium on marketable securities	-2,002	-1,811	'
Amortization of premium on marketable securities	2,120	1,262	590
Benefit from deferred income taxes	-15,211	'	'
Income tax benefit from exercise of stock options	-110	'	'
Change in operating assets and liabilities:	'	'	'
Accounts receivable	-916	241	-788
Unbilled receivables	-1,986	1,109	-1,893
Prepaid expenses and other current assets	568	-307	-235
Other assets	'	22	5
Accounts payable	399	115	763
Accrued expenses	-183	-285	1,726
Deferred revenue	-10	-7	17
Other long-term liabilities	-130	-147	498
Net cash provided by operating activities	20,179	10,653	22,623
Cash flows from investing activities	'	'	'
Purchases of property and equipment	-1,028	-606	-252
Proceeds from sales of property and equipment	3	'	66
Purchases of marketable securities	-98,405	-115,888	-47,694
Sales of marketable securities	8,421	5,453	15,750
Maturities of marketable securities	91,506	41,825	12,950
Change in restricted cash	'	'	1,140
Net cash provided by (used in) investing activities	497	-69,216	-18,040
Cash flows from financing activities	'	'	'
Proceeds from initial public offering, net of underwriting discounts and commissions	'	59,892	'
Proceeds from exercise of stock options	1,054	559	141
Payments of initial public offering costs	'	-3,540	-1,050
Income tax benefit from exercise of stock options	110	'	'
Net cash provided by (used in) financing activities	1,164	56,911	-909
Net increase (decrease) in cash and cash equivalents	21,840	-1,652	3,674
Cash and cash equivalents at beginning of period	8,859	10,511	6,837
Cash and cash equivalents at end of period	30,699	8,859	10,511
Supplemental disclosure of cash flow information:	'	'	'
Cash paid for income taxes	148	'	'
Supplemental disclosure of noncash financing activities:	'	'	'
Accretion of redeemable convertible preferred stock to redemption value	'	2,526	5,367
Deferred initial public offering costs included in accounts payable and accrued expenses	'	'	1,079
Conversion of preferred stock into common stock	'	161,808	'
Exercise of Series 1 warrants into Series 1 nonconvertible preferred stock	$206	'	'

Nature_of_the_Business

Nature of the Business	12 Months Ended
	Sep. 30, 2014
Accounting Policies [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 chemistry-driven approach and drug discovery capabilities to create small molecule drugs primarily in the infectious disease field. The Company has programs to develop novel protease, NS5A, cyclophilin and nucleotide polymerase inhibitors targeted against the hepatitis C virus (“HCV”). Additionally, the Company has programs to discover new chemical entities for 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_Account

Summary of Significant Accounting Policies	12 Months Ended
	Sep. 30, 2014
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 three months 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 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, 2014, 2013 or 2012.
	Restricted Cash
	As of September 30, 2014 and 2013, the Company had outstanding a letter of credit collateralized by a money market account of $436 to the benefit of the landlord of the Company’s current office lease. This amount was classified as long-term restricted cash as of September 30, 2014 and 2013.
	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, 2014, accounts receivable and unbilled receivables consisted solely of amounts due under the U.S. government contract. As of September 30, 2013, accounts receivable and unbilled receivables consisted of amounts due from the Company’s collaborators and under the U.S. government contract (see Note 7).
	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		3–5 years
	Leasehold improvements		Shorter of life of lease or estimated useful life
	Purchased software		3–5 years
	Computer equipment		3–5 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 is 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.
	For agreements entered into prior to October 1, 2011, the Company evaluated license agreements with multiple deliverables to determine if the deliverable elements could be recognized separately by considering (i) if the delivered elements (typically the license) had standalone value to the customer, (ii) if the fair value of any undelivered elements (typically the research and development services and the steering committee activities) could be determined based on vendor-specific objective evidence (“VSOE”) or vendor objective evidence (“VOE”), and (iii) if the arrangement included a general right of return relative to the delivered item, the delivery or performance of the undelivered item was considered probable and substantially within the control of the Company. VSOE of fair value was based on the consistent price of a deliverable when the Company regularly sold it on a standalone basis. Alternatively, VOE was based upon third-party objective evidence of fair value. If the delivered elements had value on a standalone basis and the fair value of the undelivered elements could be determined based on VSOE or VOE, revenues of such elements were then accounted for separately as delivered with arrangement consideration allocated to the delivered elements based on the residual value method. If either (i) the delivered elements were considered to not have standalone value or (ii) VSOE or VOE of fair value for any of the undelivered elements could not be determined, the arrangement was accounted for as a single unit of accounting and all payments received were recognized as revenue over the estimated period of performance of the entire arrangement.
	On October 1, 2011, the Company adopted Accounting Standards Update (“ASU”) No. 2009-13, Multiple-Deliverable Revenue Arrangements (“ASU 2009-13”). This guidance, which applies to multiple-element arrangements entered into or materially modified on or after October 1, 2011, amends the criteria for separating and allocating consideration in a multiple-element arrangement by modifying the fair value requirements for revenue recognition and eliminating the use of the residual value method. The selling prices of deliverables under the arrangement may be derived using third-party evidence (“TPE”) or a best estimate of selling price (“BESP”), if VSOE is not available. The objective of BESP is to determine the price at which the Company would transact a sale if the element within the license agreement was sold on a standalone basis. Establishing BESP involves management’s judgment and considers multiple factors, including market conditions and company-specific factors including those factors contemplated in negotiating the agreements as well as internally developed models that include assumptions related to market opportunity, discounted cash flows, estimated development costs, probability of success, and the time needed to commercialize a product candidate pursuant to the license. In validating the Company’s BESP, the Company considers whether changes in key assumptions used to determine the BESP will have a significant effect on the allocation of the arrangement consideration between the multiple deliverables. Deliverables under the arrangement are separate units of accounting if (i) the delivered item has value to the customer on a standalone basis, and (ii) if the arrangement includes a general right of return relative to the delivered item, delivery or performance of the undelivered item is considered probable and substantially within the control of the Company. The arrangement consideration that is fixed or determinable at the inception of the arrangement is allocated to the separate units of accounting based on their relative selling prices. The appropriate revenue recognition model is applied to each element, and revenue is accordingly recognized as each element is delivered. The Company may exercise significant judgment in determining whether a deliverable is a separate unit of accounting. The Company elected to adopt ASU 2009-13 prospectively as of October 1, 2011.
	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.
	Under a collaborative research and license agreement, a steering committee is typically responsible for overseeing the general working relationships, determining the protocols to be followed in the research and development performed, and evaluating the results from the continued development of the product in order to determine the clinical studies to be performed. The Company evaluates whether its participation in joint research and development steering committees is a substantive obligation or whether the services are considered inconsequential or perfunctory. The Company’s participation on a steering committee is considered “participatory” and therefore accounted for as a separate element when the collaborator requires the participation of the Company to ensure all elements of an arrangement are maximized. Steering committee services that are considered participatory are combined with other research services or performance obligations required under an arrangement, if any, in determining the level of effort required in an arrangement and the period over which the Company expects to complete its aggregate performance obligations. Alternatively, the Company’s participation on a steering committee is considered “protective” and therefore not accounted for as a separate element in a case where the Company can exercise or control when to be involved at its own discretion. Factors the Company considers in determining if its participation in a joint steering committee is participating or protective include: (i) which party negotiated or requested the steering committee, (ii) how frequently the steering committee meets, (iii) whether or not there are any penalties or other recourse if the Company does not attend the steering committee meetings, (iv) which party has decision making authority on the steering committee, and (v) whether or not the collaborator has the requisite experience and expertise associated with the research and development of the licensed intellectual property.
	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 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, if any, is recognized based on contractual terms when reported sales are reliably measurable and collectibility is reasonably assured, provided that there are no performance obligations then remaining. To date, none of the Company’s products have been approved, and therefore the Company has not earned any royalty revenue from product sales.
	During the years ended September 30, 2014, 2013 and 2012, the Company also generated revenue from a government contract under which the Company is reimbursed for certain allowable costs incurred 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 expense in the statements of operations.
	Amounts received prior to satisfying all revenue recognition criteria are recorded as deferred revenue in the accompanying balance sheets. Amounts not expected to be recognized as revenue within the next twelve months of the 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 portion of the upfront payment that had not previously been recorded as revenue but was 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 using the Black-Scholes option-pricing model. 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 issued 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. For periods in which the Company has reported net losses, diluted net loss per share attributable to common stockholders is the same as basic net loss per share attributable to common stockholders, since dilutive common shares are not assumed to have been issued if their effect is anti-dilutive.
	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 in the infectious disease field. 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 ASU No. 2014-09, Revenue from Contracts with Customers (Topic 606), which supersedes all existing revenue recognition requirements, including most industry-specific guidance. The new standard requires a company to recognize revenue when it transfers goods or services to customers in an amount that reflects the consideration that the company expects to receive for those goods or services. The new standard will be effective for the Company on October 1, 2017. The Company is currently evaluating the potential impact that Topic 606 may have on its financial position and results of operations.
	Other accounting standards that have been issued or proposed by the FASB or other standards-setting bodies that do not require adoption until a future date are not expected to have a material impact on the Company’s financial statements upon adoption.

Fair_Value_of_Financial_Assets

Fair Value of Financial Assets and Liabilities	12 Months Ended
	Sep. 30, 2014
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, 2014 and 2013 and indicate the fair value hierarchy of the valuation inputs utilized to determine such fair value:
		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 as of September 30, 2013 Using:
		Level 1			Level 2		Level 3		Total
	Assets:
	Cash equivalents	$	7,517		$	—	$	—	$	7,517
	U.S. Treasury notes		1,005			—		—		1,005
	Commercial paper		—			10,596		—		10,596
	Corporate bonds		—			84,755		—		84,755
	U.S. Agency bonds		—			3,518		—		3,518
	Certificate of deposit		—			3,450		—		3,450
		$	8,522		$	102,319	$	—	$	110,841
	Liabilities:
	Warrant liability	$	—		$	—	$	1,620	$	1,620
		$	—		$	—	$	1,620	$	1,620
	Cash equivalents at September 30, 2014 and 2013 consist of money market funds.
	During the years ended September 30, 2014, 2013 and 2012, there were no transfers between Level 1, Level 2 and Level 3.
	As of September 30, 2014 and 2013, 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. At September 30, 2014 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 a Level 3 measurement within the fair value hierarchy. The Company utilized a probability weighted valuation model which takes into consideration various outcomes that may require the Company to transfer assets upon exercise. The fair value of outstanding warrants to purchase our Series 1 nonconvertible preferred stock was $1,584 and $1,620 at September 30, 2014 and 2013, respectively. The fair value of Series 1 nonconvertible preferred stock was $202 as of September 30, 2014. 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, 2014
		Unobservable Input		Range
				(Weighted
				Average)
	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%
	September 30, 2013
		Unobservable Input		Range
				(Weighted
				Average)
	Warrant liability	Probabilities of payout		25% - 90%
		Periods in which payout is expected to occur		2014 - 2018
		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 E preferred stock and 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, 2011		1,993
	Warrants expired		(8	)
	Increase in fair value		19
	Decrease in fair value		(3	)
	Balance, September 30, 2012		2,001
	Warrants expired		(20	)
	Decrease in fair value		(361	)
	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

Marketable_Securities

Marketable Securities	12 Months Ended
	Sep. 30, 2014
Investments, Debt and Equity Securities [Abstract]	'
Marketable Securities	'
	4. Marketable Securities
	As of September 30, 2014 and 2013, the fair value of available-for-sale marketable securities by type of security was as follows:
		September 30, 2014
		Amortized Cost		Gross Unrealized		Gross Unrealized			Fair Value
				Gains		Losses
	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
		September 30, 2013
		Amortized Cost		Gross Unrealized		Gross Unrealized			Fair Value
				Gains		Losses
	Commercial paper	$	10,596	$	—	$	—		$	10,596
	Corporate bonds		84,757		23		(25	)		84,755
	U.S. Agency bonds		3,519		—		(1	)		3,518
	Certificate of deposit		3,450		—		—			3,450
	U.S. Treasury notes		1,004		1		—			1,005
		$	103,326	$	24	$	(26	)	$	103,324
	At September 30, 2014, marketable securities consisted of investments that mature within one year, with the exception of certain corporate and U.S. Agency bonds, which have maturities within three years and an aggregate fair value of $41,003. At September 30, 2013, marketable securities consisted of investments that mature within one year, with the exception of one U.S. Treasury note and one corporate bond, which have maturities within two years and an aggregate fair value of $10,703.

Property_and_Equipment

Property and Equipment	12 Months Ended
	Sep. 30, 2014
Property, Plant and Equipment [Abstract]	'
Property and Equipment	'
	5. Property and Equipment
	Property and equipment consisted of the following as of September 30, 2014 and 2013:
		September 30,
		2014			2013
	Laboratory and office equipment	$	4,829		$	4,395
	Leasehold improvements		300			272
	Purchased software		414			438
	Computer equipment		111			90
	Furniture		284			263
			5,938			5,458
	Less: Accumulated depreciation and amortization		(4,135	)		(4,337	)
		$	1,803		$	1,121
	Depreciation and amortization expense was $352, $221 and $172 for the years ended September 30, 2014, 2013 and 2012, respectively. During the years ended September 30, 2014, 2013 and 2012, assets with a cost of $554, $420 and $273, respectively, were sold or disposed of, resulting in gains of $3, $100 and $63, respectively.

Accrued_Expenses_and_Other_Lon

Accrued Expenses and Other Long-Term Liabilities	12 Months Ended
	Sep. 30, 2014
Payables and Accruals [Abstract]	'
Accrued Expenses and Other Long-Term Liabilities	'
	6. Accrued Expenses and Other Long-Term Liabilities
	Accrued expenses (current) and other long-term liabilities consisted of the following as of September 30, 2014 and 2013:
		September 30,
		2014		2013
	Accrued expenses:
	Accrued payroll and related expenses	$	1,275	$	1,041
	Accrued preclinical and clinical expenses		493		—
	Accrued vendor manufacturing		116		989
	Accrued professional fees		436		378
	Accrued third-party license fee		240		240
	Accrued other		312		387
		$	2,872	$	3,035
	Other long-term liabilities:
	Accrued rent expense	$	153	$	127
	Present value of accrued third-party license fee		—		184
	Asset retirement obligation		76		48
		$	229	$	359

Collaboration_Agreements

Collaboration Agreements	12 Months Ended
	Sep. 30, 2014
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, which was amended in January and December 2009, 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 year ended September 30, 2013, the Company received a $15,000 milestone payment under the AbbVie Agreement as a result of AbbVie’s initiation of dosing in a Phase 3 clinical trial of a regimen that included paritaprevir. During the year ended September 30, 2014, the Company received $40,000 in milestone payments as a result of the regulatory filings by AbbVie with the FDA and the EMA. From commencement of collaboration, through September 30, 2014, the Company has received a total of $160,000 under the AbbVie Agreement consisting of an upfront license payment, research funding, milestone payments and preferred stock financing. As of September 30, 2014, the Company is eligible to receive additional milestone payments totaling up to $155,000 upon AbbVie’s achievement of commercial regulatory approval milestones in selected world markets. The Company is also eligible to receive additional milestone payments totaling up to $80,000 upon AbbVie’s achievement of similar commercial regulatory approval milestones for each additional product containing a protease inhibitor. Under the terms of this agreement, as amended in October 2014, 30% of net sales of a 3-DAA regimen containing paritaprevir will be allocated to paritaprevir, 45% of net sales of a 2-DAA regimen containing paritaprevir will be allocated to paritaprevir. For ABT-493, 50% of net sales of a 2-DAA regimen containing ABT-493 will be allocated to ABT-493 and 33 1⁄3% of such net sales will be allocated to a 3-DAA regimen containing ABT-493. If there is any active ingredient other than DAA’s in any ABT-493-containing regimen sold by AbbVie, there will be a further adjustment to net sales based on the relative value of the non-DAA ingredient.
	Since the Company completed all its performance obligations under the AbbVie Agreement by the end of fiscal 2011, any future milestone payments received have been and will be recognized as revenue when achieved by AbbVie. No revenue related to this agreement was recognized during the year ended September 30, 2012.
	The Company has 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
	On February 16, 2012, the Company entered into a license and collaboration agreement with Novartis (the “Novartis Agreement”) for the development, manufacture and commercialization of its lead development candidate, EDP-239, from its NS5A HCV inhibitor program. Under the terms of the Novartis Agreement, Novartis paid a nonrefundable upfront fee to the Company and reimbursement of manufacturing and quality assurance expenses related to EDP-239 totaling $34,442, and a clinical milestone payment of $11,000 was earned and recognized as revenue in fiscal 2013. In addition, Novartis funded research activities for 18 months commencing February 2012, up to a total of $2,700.
	The Company determined that the deliverables under the Novartis Agreement included (i) the exclusive, royalty-bearing, sublicensable license to EDP-239 and (ii) the research services. The Company concluded that the EDP-239 license had standalone value to Novartis and was separable from the research services as the license is sublicensable, there are no restrictions as to Novartis’ use of the license and Novartis has the requisite scientific expertise in the HCV NS5A field. The Company also concluded that its participation on the joint steering committee, as provided by the agreement, is protective in nature as the Company has no decision making authority, there are no penalties or recourse if the Company chooses not to participate, and the purpose of the steering committee is to keep the Company apprised as to the status of the development and commercialization efforts. Therefore, no arrangement consideration was allocated to the joint steering committee participation. The Company was not able to establish VSOE or TPE for either the license or the research services and instead allocated the arrangement consideration between the license and research services based on their relative selling prices using BESP. The Company developed its estimate of BESP of the license using a discounted cash flow analysis, taking into consideration assumptions including the development and commercialization timeline, discount rate, probability of success, and probable treatment combination and associated peak sales figures that generate royalty amounts. The funding rate for the research services is consistent with the rate received in the Company’s prior collaboration arrangement with AbbVie and is consistent with its fully burdened cost of service. Therefore, the Company’s determination of BESP for the research services is consistent with the reimbursement rate stated in the contract. These assumptions involve judgment and inherent uncertainty; however, significant changes in key assumptions used to determine the BESP would not have a significant effect on the total amount of revenue recognized.
	The Company recognized the entire upfront cash receipt as revenue because the allocated selling price of the license deliverable exceeded the upfront noncontingent cash payments received. During the year ended September 30, 2012, the Company recognized total revenue of $35,567 related to the delivery of the license and the performance of the research services.
	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.
	On September 30, 2014 the Company entered into an amendment to its 2012 Collaboration and License Agreement with Novartis to return to the Company full rights to its NS5A inhibitor program, including EDP-239. This agreement provides for the completing of transition to the Company of the proof-of-concept clinical study currently underway involving EDP-239, as well as all rights of Novartis in the NS5A program.
	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”), which contract could provide up to $42,700 in development funding to the Company over a five-year period. Under this contract NIAID has funded 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.
	The contract had an initial term of 30 months which ended on March 30, 2014. NIAID has the option to extend the contract up to six times. If each extension option is exercised, the contract would be extended until September 30, 2016. The initial award under the initial term was $14,300, with the possibility of up to a total of $42,700 if each option period is exercised by NIAID.
	In August 2013 NIAID exercised the first two options under this agreement which obligated it to provide an additional $9,200 in funding to the Company for preclinical and early clinical development of its lead antibiotic candidate, bringing total funding paid or committed to date by NIAID to approximately $23,500 through February 2015.
	The Company recognizes revenue under this agreement as development services are performed in accordance with the funding agreement. During the year ended September 30, 2012, $6,139 of revenue was recognized under this agreement, of which $1,049 was invoiced but unpaid and included in accounts receivable and $1,668 was unpaid and included in unbilled receivables on the Company’s balance sheet as of September 30, 2012. During the year ended September 30, 2013, the Company recognized revenue of $4,378, under this agreement, of which $258 was invoiced but unpaid and included in accounts receivable and $784 was unpaid and included in unbilled receivables at September 30, 2013. During the year ended September 30, 2014, the Company recognized revenue of $7,741, under this agreement, 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.
	NIAID may terminate performance of work under this contract if it determines that a termination is in the government’s interest, also referred to as for convenience, or if the Company defaults in performing the contract. In light of the Company’s strategic decision not to continue commercial development of the antibiotic candidate for non-biodefense indications, which it communicated to NIAID in December 2014, the Company expects that NIAID will likely exercise its right to terminate this contract for convenience in accordance with its terms. After termination, the Company would submit a final termination settlement proposal in order to settle all outstanding liabilities, including those arising from the termination of subcontracts, the cost of which would be reimbursable in whole or in part, under this contract, contingent on approval by NIAID. If the Company and NIAID fail to agree in whole or in part on the amount of costs to be paid because of the termination of work, NIAID shall determine, on the basis of information available, the amount to be paid to the Company.

Stockholders_Equity

Stockholders' Equity	12 Months Ended
	Sep. 30, 2014
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.
	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. As of September 30, 2014 and 2013 there were 223,153 and 0 shares of Series 1 nonconvertible preferred issued and outstanding, respectively. 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.
	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.

Preferred_Stock_Warrants

Preferred Stock Warrants	12 Months Ended
	Sep. 30, 2014
Text Block [Abstract]	'
Preferred Stock Warrants	'
	9. Preferred Stock Warrants
	Warrants to Purchase Series E Preferred Stock
	Warrants for the purchase of Series E redeemable convertible preferred stock (“Series E preferred stock”) were issued by the Company in fiscal 2002 and fiscal 2004 during various financings. As these warrants were financial instruments that would require a transfer of assets because of the redemption feature at the option of the holders of the Series E preferred stock, these warrants were classified as liabilities on the Company’s balance sheet at September 30, 2012.
	As of September 30, 2011, warrants for the purchase of 341,556 shares of Series E preferred stock were outstanding. During the year ended September 30, 2012, warrants for the purchase of 329,056 shares expired. As of September 30, 2012, warrants for the purchase of 12,500 shares of Series E preferred stock remained outstanding. These warrants expired during the year ended September 30, 2013.
	The Company is required to remeasure the fair value of these preferred stock warrants at each reporting date, with any adjustments recorded as other income (expense). The warrants outstanding at each reporting date were remeasured using the Black-Scholes option-pricing model, and the resulting change in fair value was recorded in other income (expense) in the statement of operations. As a result, the Company recorded expense of $19 for the year ended September 30, 2012, related to the change in fair value of the warrants. The Company also recorded income of $8 for the year ended September 30, 2012 related to the expiration of 329,056 warrants. As of September 30, 2012, the total fair value of the outstanding Series E preferred stock warrants was $20. During the year ended September 30, 2013, the Company recorded income of $20 related to the expiration of the Series E preferred stock warrants.
	Warrants to Purchase Series 1 Nonconvertible Preferred Stock
	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, these warrants are classified as liabilities. These 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. As of September 30, 2014, the total fair value of the Series 1 nonconvertible preferred stock was $202. The warrants and Series 1 nonconvertible preferred stock were remeasured at each reporting period, resulting in expense of $166, income of $361 and expense of $16 for the years ended September 30, 2014, 2013 and 2012, respectively. As of September 30, 2014 and September 30, 2013, the total fair value of the Series 1 nonconvertible preferred stock warrants was $1,584 and $1,620, respectively.
	The following table summarizes the Company’s warrant activity since October 1, 2011:
		Series E			Weighted		Series 1			Weighted
		Preferred			Average		Nonconvertible			Average
		Stock			Exercise		Preferred			Exercise
		Exercisable			Price		Stock			Price
							Exercisable
	Outstanding, as of September 30, 2011		341,556		$	2.51		1,999,989		$	0.01
	Granted		—					—
	Expired		(329,056	)				—
	Exercised		—					—
	Outstanding, as of September 30, 2012		12,500		$	2.51		1,999,989		$	0.01
	Granted		—					—
	Expired		(12,500	)				—
	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

StockBased_Awards

Stock-Based Awards	12 Months Ended
	Sep. 30, 2014
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]	'
Stock-Based Awards	'
	10. Stock-Based Awards
	In 2012 the Company’s Board adopted the 2012 Equity Incentive Plan (the “2012 Plan”), which was subsequently approved by the stockholders and became effective immediately prior to the closing of the Company’s initial public offering on March 26, 2013. The 2012 Plan permits the Company to sell or issue common stock or restricted common stock, and to grant incentive stock options or nonqualified stock options for the purchase of common stock, restricted stock 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, 2013, the number of shares of common stock that might be issued under the 2012 Plan was increased by 538,102 shares. As of September 30, 2014, 412,943 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.
	On January 3, 2013, the Company’s stockholders approved an Employee Stock Purchase Plan (“ESPP”). A total of 185,614 shares of common stock are reserved for issuance under this plan, which became effective immediately prior the closing of the Company’s initial public offering. As of September 30, 2014, the Company had not commenced any offering under the ESPP and no 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 year ended September 30, 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. Prior to March 2013 the Company historically had been a private company and lacked sufficient company-specific historical and implied volatility information. Therefore, it estimates its expected stock volatility based on the historical volatility of a selected group of publicly traded peer companies, inclusive of the Company, commencing March 2013, 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:
		Year Ended September 30,
		2014			2013			2012
	Risk-free interest rate		1.89	%		1.05	%		0.93	%
	Expected term (in years)		6.06			6.09			6
	Expected volatility		75	%		73	%		78	%
	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, 2014:
		Shares			Weighted			Weighted			Aggregate
		Issuable			Average			Average			Intrinsic
		Under			Exercise			Remaining			Value
		Options			Price			Contractual
								Term
								(in years)
	Outstanding as of September 30, 2013		1,583,031		$	5.15			5		$	28,133
	Granted		488,570			29.83
	Exercised		(664,793	)		1.61
	Forfeited		(16,906	)		16.64
	Expired		(465	)		0.73
	Outstanding as of September 30, 2014		1,389,437		$	15.39			7.2		$	33,573
	Options vested and expected to vest as of September 30, 2014		1,209,316		$	15.47			7		$	29,126
	Options exercisable as of September 30, 2014		708,010		$	7.37			5.6		$	22,767
	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 $3,219, $7,574 and $606 during the years ended September 30, 2014, 2013 and 2012, respectively.
	The Company received cash proceeds from the exercise of stock options of $1,054, $559 and $141 during the years ended September 30, 2014, 2013 and 2012, respectively. The weighted average grant date fair value of options granted during the years ended September 30, 2014, 2013 and 2012 was $19.98, $9.16 and $7.79, respectively.
	The Company recorded stock-based compensation expense for the years ended September 30, 2014, 2013 and 2012 in the following expense categories:
		Year Ended September 30,
		2014			2013			2012
	Research and development	$	762		$	393		$	126
	General and administrative		1,920			670			298
		$	2,682		$	1,063		$	424
	As of September 30, 2014, the Company had an aggregate of $8,467 of unrecognized stock-based compensation cost, which is expected to be recognized over a weighted average period of 3.1 years.

Net_Income_Loss_Per_Share

Net Income (Loss) Per Share	12 Months Ended
	Sep. 30, 2014
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, 2014, 2013 and 2012:
		Year Ended September 30,
		2014		2013			2012
	Basic net income (loss) per share attributable to common stockholders:
	Numerator:
	Net income	$	34,438	$	9,627		$	21,399
	Accretion of redeemable convertible preferred stock to redemption value		—		(2,526	)		(5,367	)
	Net income attributable to participating securities		—		(13,670	)		(14,663	)
	Net income (loss) attributable to common stockholders	$	34,438	$	(6,569	)	$	1,369
	Denominator:
	Weighted average common shares outstanding—basic		18,354,791		9,788,039			1,088,784
	Net income (loss) per share attributable to common stockholders—basic	$	1.88	$	(0.67	)	$	1.26
		Year Ended September 30,
		2014		2013			2012
	Diluted net income (loss) per share attributable to common stockholders:
	Numerator:
	Net income	$	34,438	$	9,627		$	21,399
	Accretion of redeemable convertible preferred stock to redemption value		—		(2,526	)		(5,367	)
	Net income attributable to participating securities		—		(13,670	)		(13,225	)
	Net income (loss) attributable to common stockholders—diluted	$	34,438	$	(6,569	)	$	2,807
	Denominator:
	Weighted average common shares outstanding—basic		18,354,791		9,788,039			1,088,784
	Dilutive effect of common stock equivalents		830,437		—			1,386,039
	Weighted average common shares outstanding—diluted		19,185,228		9,788,039			2,474,823
	Net income (loss) per share attributable to common stockholders—diluted	$	1.8	$	(0.67	)	$	1.13
	Stock options for the purchase of 330,430, 1,713,313 and 33,359 weighted average shares were excluded from the computation of diluted net income per share attributable to common stockholders for the years ended September 30, 2014, 2013 and 2012, 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, 2014
Commitments and Contingencies Disclosure [Abstract]	'
Commitments and Contingencies	'
	12. Commitments and Contingencies
	Leases
	During the year ended September 30, 2011, the Company signed a seven-year lease for new office space that began on October 1, 2011. The lease provides for payment escalations during the term of the lease. Payment escalations as specified in the lease agreements are accrued such that rent expense is recognized on a straight-line basis over the terms of occupancy. The Company incurred rent expense of $948, for each of the years ended September 30, 2014, 2013 and 2012.
	Future minimum lease payments for operating leases as of September 30, 2014 are as follows:
	Year ending September 30,
	2015	$	946
	2016		972
	2017		999
	2018		1,027
	Total	$	3,944
	In connection with the current lease, the Company issued a $436 letter of credit, collateralized by a money market account. As of September 30, 2014 and 2013, the Company classified amounts of $436 in each year, as restricted cash relating to this lease.
	Intellectual Property Licenses
	During the year ended September 30, 2012, in response to correspondence the Company received from a third party related to assets the Company used or may have used in prior periods, the Company entered into a non-exclusive intellectual property license agreement with the third party. Under the 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 a result, during fiscal 2012, the Company recorded in research and development expense a total of $895 of license expense, which represented the fair value of the payments that the Company believed related to its use of the assets in fiscal 2012 and prior periods. As of September 30, 2012, the Company had recorded liabilities totaling $995 related to the agreement. During the years ended September 30, 2014 and 2013, the Company paid $250 and $350, respectively, under the agreement. As of September 30, 2014, the Company had recorded liabilities totaling $192 in connection with the agreement, which were included in accrued expenses.
	As of September 30, 2012, the Company was aware of a potential license it may need to acquire with respect to patents it used, or may have used, in its HCV research during prior years or periods. As of September 30, 2012, the Company believed that license costs were probable, but a range of the loss could not be reasonably estimated; therefore, no accrual for this matter was recorded as of September 30, 2012. 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 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 will be required to obtain licenses and could be required to pay license fees or royalties, or both. These licenses may not be available on acceptable terms, or at all. A costly license, or inability to obtain a necessary license, 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, 2014 or 2013.

Income_Taxes

Income Taxes	12 Months Ended
	Sep. 30, 2014
Income Tax Disclosure [Abstract]	'
Income Taxes	'
	13. Income Taxes
	Income before income taxes for all periods presented is solely from domestic operations. During the year ended September 30, 2014, the Company recorded a provision for income taxes as follows:
	Current tax expense:
	Federal	$	—
	State		151
	Deferred tax benefit:
	Federal		(13,048	)
	State		(2,273	)
	Total tax benefit	$	(15,170	)
	During the years ended September 30, 2013 and 2012 no provision for income taxes was recorded due primarily to the Company’s use of net operating loss carryforwards to offset fully the income before income taxes of $9,627 and $21,399, respectively, generated in those periods. 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 each of those periods resulted in an income tax benefit being recognized, which offset the tax provision recorded as a result of the income before income taxes generated.
	The effective tax rate benefit 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 and 2012 was 0% and differed 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. The Company had concluded in that period, based on the weight of available evidence, that its net deferred tax assets were not more likely than not to be realized in the future. Accordingly, a full valuation allowance had been established against the deferred tax assets as of September 30, 2013 and 2012.
	A reconciliation of the U.S. federal statutory income tax rate to the Company’s effective income tax rate is as follows:
		Year Ended September 30,
		2014			2013			2012
	Federal statutory income tax rate		35	%		34	%		34	%
	State taxes, net of federal benefit		5.5			5.5			5.4
	Federal research and development tax credit		(0.5	)		(2.5	)		(0.2	)
	Change in deferred tax asset valuation allowance		(118.8	)		(51.0	)		(40.1	)
	Change in statutory rate		(2.1	)		—			—
	Other		2.2			14			0.9
	Effective income tax rate		(78.7	)%		0	%		0	%
	Net deferred tax assets as of September 30, 2014 and 2013 consisted of the following:
		September 30,
		2014			2013
	Net operating loss carryforwards	$	2,952		$	8,495
	Tax credit carryforwards		5,920			6,111
	Capitalized research and development expenses		4,756			6,953
	Other temporary differences		1,693			1,333
	Gross deferred tax assets		15,321			22,892
	Valuation allowance		—			(22,892	)
	Net deferred tax assets	$	15,321		$	—
	As of September 30, 2014, the Company had net operating loss carryforwards for federal and state income tax purposes of $8,433 and $0, respectively, of which the federal carryforward begins to expire in fiscal 2018. The Company also has 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 begin to expire in fiscal 2021 and 2018, respectively. Utilization of the net operating loss carryforwards and research and development tax credit carryforwards may be subject to a substantial annual limitation under Section 382 of the Internal Revenue Code of 1986 due to ownership changes that could occur in the future. These ownership changes may limit the amount of carryforwards that can be utilized annually to offset future taxable income.
	During the years ended September 30, 2014, 2013 and 2012, gross deferred tax assets related to net operating loss carryforwards decreased due to their utilization as a result of income before income taxes generated during those periods.
	Through March 31, 2014, the Company had provided a valuation allowance for the full amount of its net deferred tax assets because it was not more likely than not that any future benefit from deductible temporary differences and net operating loss and tax credit carry forwards would be realized. As of June 30, 2014, the Company reassessed the need for a valuation allowance against its deferred tax assets as the Company earned and collected $40,000 in milestone payments during the three months ended June 30, 2014 as a result of U.S. and European Union regulatory approval filing by AbbVie with respect to the collaboration’s leading product candidate. The Company concluded that it was more likely than not that it 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 collaboration partners. Accordingly, the Company released its valuation allowance and recorded an income tax benefit of approximately $15,122 for the period ended June 30, 2014. The reversal of the valuation allowance released approximately $22,892, of which $15,333 was recorded in the period ended June 30, 2014 representing the change in estimate regarding future years’ income, and the remaining $7,559 was released to income as the deferred tax assets were utilized in fiscal 2014.
	Changes in the valuation allowance for deferred tax assets during the years ended September 30, 2014, 2013 and 2012 were as follows:
		Year Ended September 30,
		2014			2013			2012
	Valuation allowance as of beginning of year	$	22,892		$	27,799		$	36,369
	Decreases recorded as benefit to income tax provision		(22,892	)		(4,907	)		(8,570	)
	Valuation allowance as of end of year	$	—		$	22,892		$	27,799
	In all periods presented, all income before income taxes was sourced from the United States.
	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 2007 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 no unrecognized tax benefits September 30, 2014, 2013 and 2012. 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.

401k_Plan

401(k) Plan	12 Months Ended
	Sep. 30, 2014
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, 2014, 2013 and 2012, the Company recognized $180, $90 and $84, respectively, of expense related to its contributions to this plan.

Selected_Quarterly_Financial_D

Selected Quarterly Financial Data (unaudited)	12 Months Ended
	Sep. 30, 2014
Quarterly Financial Information Disclosure [Abstract]	'
Selected Quarterly Financial Data (unaudited)	'
	15. Selected Quarterly Financial Data (unaudited)
	Quarterly financial information for fiscal 2014 and 2013 is presented in the following table, in thousands, except per share data:
		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	)	$	2.7		$	(0.27	)
	Net income (loss) per share attributable to common shareholders—diluted	$	(0.30	)	$	(0.28	)	$	2.61		$	(0.27	)
		2013 Quarter Ended
		December 31, 2012			March 31, 2013			June 30, 2013			September 30, 2013
	Revenue	$	27,859		$	1,196		$	1,649		$	1,349
	Operating expenses		5,950			5,197			5,827			6,050
	Other income (expense), net		48			252			40			258
	Net income (loss)		21,957			(3,749	)		(4,138	)		(4,443	)
	Net income (loss) per share attributable to common shareholders—basic	$	1.61		$	(2.28	)	$	(0.23	)	$	(0.25	)
	Net income (loss) per share attributable to common shareholders—diluted	$	1.45		$	(2.28	)	$	(0.23	)	$	(0.25	)

Summary_of_Significant_Account1

Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Sep. 30, 2014
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 three months 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 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, 2014, 2013 or 2012.
Restricted Cash	'
	Restricted Cash
	As of September 30, 2014 and 2013, the Company had outstanding a letter of credit collateralized by a money market account of $436 to the benefit of the landlord of the Company’s current office lease. This amount was classified as long-term restricted cash as of September 30, 2014 and 2013.
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, 2014, accounts receivable and unbilled receivables consisted solely of amounts due under the U.S. government contract. As of September 30, 2013, accounts receivable and unbilled receivables consisted of amounts due from the Company’s collaborators and under the U.S. government contract (see Note 7).
	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		3–5 years
	Leasehold improvements		Shorter of life of lease or estimated useful life
	Purchased software		3–5 years
	Computer equipment		3–5 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 is 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.
	For agreements entered into prior to October 1, 2011, the Company evaluated license agreements with multiple deliverables to determine if the deliverable elements could be recognized separately by considering (i) if the delivered elements (typically the license) had standalone value to the customer, (ii) if the fair value of any undelivered elements (typically the research and development services and the steering committee activities) could be determined based on vendor-specific objective evidence (“VSOE”) or vendor objective evidence (“VOE”), and (iii) if the arrangement included a general right of return relative to the delivered item, the delivery or performance of the undelivered item was considered probable and substantially within the control of the Company. VSOE of fair value was based on the consistent price of a deliverable when the Company regularly sold it on a standalone basis. Alternatively, VOE was based upon third-party objective evidence of fair value. If the delivered elements had value on a standalone basis and the fair value of the undelivered elements could be determined based on VSOE or VOE, revenues of such elements were then accounted for separately as delivered with arrangement consideration allocated to the delivered elements based on the residual value method. If either (i) the delivered elements were considered to not have standalone value or (ii) VSOE or VOE of fair value for any of the undelivered elements could not be determined, the arrangement was accounted for as a single unit of accounting and all payments received were recognized as revenue over the estimated period of performance of the entire arrangement.
	On October 1, 2011, the Company adopted Accounting Standards Update (“ASU”) No. 2009-13, Multiple-Deliverable Revenue Arrangements (“ASU 2009-13”). This guidance, which applies to multiple-element arrangements entered into or materially modified on or after October 1, 2011, amends the criteria for separating and allocating consideration in a multiple-element arrangement by modifying the fair value requirements for revenue recognition and eliminating the use of the residual value method. The selling prices of deliverables under the arrangement may be derived using third-party evidence (“TPE”) or a best estimate of selling price (“BESP”), if VSOE is not available. The objective of BESP is to determine the price at which the Company would transact a sale if the element within the license agreement was sold on a standalone basis. Establishing BESP involves management’s judgment and considers multiple factors, including market conditions and company-specific factors including those factors contemplated in negotiating the agreements as well as internally developed models that include assumptions related to market opportunity, discounted cash flows, estimated development costs, probability of success, and the time needed to commercialize a product candidate pursuant to the license. In validating the Company’s BESP, the Company considers whether changes in key assumptions used to determine the BESP will have a significant effect on the allocation of the arrangement consideration between the multiple deliverables. Deliverables under the arrangement are separate units of accounting if (i) the delivered item has value to the customer on a standalone basis, and (ii) if the arrangement includes a general right of return relative to the delivered item, delivery or performance of the undelivered item is considered probable and substantially within the control of the Company. The arrangement consideration that is fixed or determinable at the inception of the arrangement is allocated to the separate units of accounting based on their relative selling prices. The appropriate revenue recognition model is applied to each element, and revenue is accordingly recognized as each element is delivered. The Company may exercise significant judgment in determining whether a deliverable is a separate unit of accounting. The Company elected to adopt ASU 2009-13 prospectively as of October 1, 2011.
	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.
	Under a collaborative research and license agreement, a steering committee is typically responsible for overseeing the general working relationships, determining the protocols to be followed in the research and development performed, and evaluating the results from the continued development of the product in order to determine the clinical studies to be performed. The Company evaluates whether its participation in joint research and development steering committees is a substantive obligation or whether the services are considered inconsequential or perfunctory. The Company’s participation on a steering committee is considered “participatory” and therefore accounted for as a separate element when the collaborator requires the participation of the Company to ensure all elements of an arrangement are maximized. Steering committee services that are considered participatory are combined with other research services or performance obligations required under an arrangement, if any, in determining the level of effort required in an arrangement and the period over which the Company expects to complete its aggregate performance obligations. Alternatively, the Company’s participation on a steering committee is considered “protective” and therefore not accounted for as a separate element in a case where the Company can exercise or control when to be involved at its own discretion. Factors the Company considers in determining if its participation in a joint steering committee is participating or protective include: (i) which party negotiated or requested the steering committee, (ii) how frequently the steering committee meets, (iii) whether or not there are any penalties or other recourse if the Company does not attend the steering committee meetings, (iv) which party has decision making authority on the steering committee, and (v) whether or not the collaborator has the requisite experience and expertise associated with the research and development of the licensed intellectual property.
	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 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, if any, is recognized based on contractual terms when reported sales are reliably measurable and collectibility is reasonably assured, provided that there are no performance obligations then remaining. To date, none of the Company’s products have been approved, and therefore the Company has not earned any royalty revenue from product sales.
	During the years ended September 30, 2014, 2013 and 2012, the Company also generated revenue from a government contract under which the Company is reimbursed for certain allowable costs incurred 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 expense in the statements of operations.
	Amounts received prior to satisfying all revenue recognition criteria are recorded as deferred revenue in the accompanying balance sheets. Amounts not expected to be recognized as revenue within the next twelve months of the 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 portion of the upfront payment that had not previously been recorded as revenue but was 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 using the Black-Scholes option-pricing model. 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 (Loss) 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 issued 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. For periods in which the Company has reported net losses, diluted net loss per share attributable to common stockholders is the same as basic net loss per share attributable to common stockholders, since dilutive common shares are not assumed to have been issued if their effect is anti-dilutive.
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 in the infectious disease field. 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 ASU No. 2014-09, Revenue from Contracts with Customers (Topic 606), which supersedes all existing revenue recognition requirements, including most industry-specific guidance. The new standard requires a company to recognize revenue when it transfers goods or services to customers in an amount that reflects the consideration that the company expects to receive for those goods or services. The new standard will be effective for the Company on October 1, 2017. The Company is currently evaluating the potential impact that Topic 606 may have on its financial position and results of operations.
	Other accounting standards that have been issued or proposed by the FASB or other standards-setting bodies that do not require adoption until a future date are not expected to have a material impact on the Company’s financial statements upon adoption.

Summary_of_Significant_Account2

Summary of Significant Accounting Policies (Tables)	12 Months Ended
	Sep. 30, 2014
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	3–5 years
	Leasehold improvements	Shorter of life of lease or estimated useful life
	Purchased software	3–5 years
	Computer equipment	3–5 years
	Furniture	7 years

Fair_Value_of_Financial_Assets1

Fair Value of Financial Assets and Liabilities (Tables)	12 Months Ended
	Sep. 30, 2014
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, 2014 and 2013 and indicate the fair value hierarchy of the valuation inputs utilized to determine such fair value:
		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 as of September 30, 2013 Using:
		Level 1			Level 2		Level 3		Total
	Assets:
	Cash equivalents	$	7,517		$	—	$	—	$	7,517
	U.S. Treasury notes		1,005			—		—		1,005
	Commercial paper		—			10,596		—		10,596
	Corporate bonds		—			84,755		—		84,755
	U.S. Agency bonds		—			3,518		—		3,518
	Certificate of deposit		—			3,450		—		3,450
		$	8,522		$	102,319	$	—	$	110,841
	Liabilities:
	Warrant liability	$	—		$	—	$	1,620	$	1,620
		$	—		$	—	$	1,620	$	1,620
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, 2014
		Unobservable Input		Range
				(Weighted
				Average)
	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%
	September 30, 2013
		Unobservable Input		Range
				(Weighted
				Average)
	Warrant liability	Probabilities of payout		25% - 90%
		Periods in which payout is expected to occur		2014 - 2018
		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 E preferred stock and 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, 2011		1,993
	Warrants expired		(8	)
	Increase in fair value		19
	Decrease in fair value		(3	)
	Balance, September 30, 2012		2,001
	Warrants expired		(20	)
	Decrease in fair value		(361	)
	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

Marketable_Securities_Tables

Marketable Securities (Tables)	12 Months Ended
	Sep. 30, 2014
Investments, Debt and Equity Securities [Abstract]	'
Fair Value of Available-for-Sale Marketable Securities by Type of Security	'
	As of September 30, 2014 and 2013, the fair value of available-for-sale marketable securities by type of security was as follows:
		September 30, 2014
		Amortized Cost		Gross Unrealized		Gross Unrealized			Fair Value
				Gains		Losses
	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
		September 30, 2013
		Amortized Cost		Gross Unrealized		Gross Unrealized			Fair Value
				Gains		Losses
	Commercial paper	$	10,596	$	—	$	—		$	10,596
	Corporate bonds		84,757		23		(25	)		84,755
	U.S. Agency bonds		3,519		—		(1	)		3,518
	Certificate of deposit		3,450		—		—			3,450
	U.S. Treasury notes		1,004		1		—			1,005
		$	103,326	$	24	$	(26	)	$	103,324

Property_and_Equipment_Tables

Property and Equipment (Tables)	12 Months Ended
	Sep. 30, 2014
Property, Plant and Equipment [Abstract]	'
Schedule of Property and Equipment	'
	Property and equipment consisted of the following as of September 30, 2014 and 2013:
		September 30,
		2014			2013
	Laboratory and office equipment	$	4,829		$	4,395
	Leasehold improvements		300			272
	Purchased software		414			438
	Computer equipment		111			90
	Furniture		284			263
			5,938			5,458
	Less: Accumulated depreciation and amortization		(4,135	)		(4,337	)
		$	1,803		$	1,121

Accrued_Expenses_and_Other_Lon1

Accrued Expenses and Other Long-Term Liabilities (Tables)	12 Months Ended
	Sep. 30, 2014
Payables and Accruals [Abstract]	'
Accrued Expenses (Current) and Other Long-Term Liabilities	'
	Accrued expenses (current) and other long-term liabilities consisted of the following as of September 30, 2014 and 2013:
		September 30,
		2014		2013
	Accrued expenses:
	Accrued payroll and related expenses	$	1,275	$	1,041
	Accrued preclinical and clinical expenses		493		—
	Accrued vendor manufacturing		116		989
	Accrued professional fees		436		378
	Accrued third-party license fee		240		240
	Accrued other		312		387
		$	2,872	$	3,035
	Other long-term liabilities:
	Accrued rent expense	$	153	$	127
	Present value of accrued third-party license fee		—		184
	Asset retirement obligation		76		48
		$	229	$	359

Preferred_Stock_Warrants_Table

Preferred Stock Warrants (Tables)	12 Months Ended
	Sep. 30, 2014
Text Block [Abstract]	'
Summary of Warrant Activity	'
	The following table summarizes the Company’s warrant activity since October 1, 2011:
		Series E			Weighted		Series 1			Weighted
		Preferred			Average		Nonconvertible			Average
		Stock			Exercise		Preferred			Exercise
		Exercisable			Price		Stock			Price
							Exercisable
	Outstanding, as of September 30, 2011		341,556		$	2.51		1,999,989		$	0.01
	Granted		—					—
	Expired		(329,056	)				—
	Exercised		—					—
	Outstanding, as of September 30, 2012		12,500		$	2.51		1,999,989		$	0.01
	Granted		—					—
	Expired		(12,500	)				—
	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

StockBased_Awards_Tables

Stock-Based Awards (Tables)	12 Months Ended
	Sep. 30, 2014
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]	'
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:
		Year Ended September 30,
		2014			2013			2012
	Risk-free interest rate		1.89	%		1.05	%		0.93	%
	Expected term (in years)		6.06			6.09			6
	Expected volatility		75	%		73	%		78	%
	Expected dividend yield		0	%		0	%		0	%
Stock Option Activity	'
	The following table summarizes stock option activity for the year ended September 30, 2014:
		Shares			Weighted			Weighted			Aggregate
		Issuable			Average			Average			Intrinsic
		Under			Exercise			Remaining			Value
		Options			Price			Contractual
								Term
								(in years)
	Outstanding as of September 30, 2013		1,583,031		$	5.15			5		$	28,133
	Granted		488,570			29.83
	Exercised		(664,793	)		1.61
	Forfeited		(16,906	)		16.64
	Expired		(465	)		0.73
	Outstanding as of September 30, 2014		1,389,437		$	15.39			7.2		$	33,573
	Options vested and expected to vest as of September 30, 2014		1,209,316		$	15.47			7		$	29,126
	Options exercisable as of September 30, 2014		708,010		$	7.37			5.6		$	22,767
Stock-Based Compensation Expense	'
	The Company recorded stock-based compensation expense for the years ended September 30, 2014, 2013 and 2012 in the following expense categories:
		Year Ended September 30,
		2014			2013			2012
	Research and development	$	762		$	393		$	126
	General and administrative		1,920			670			298
		$	2,682		$	1,063		$	424

Net_Income_Loss_Per_Share_Tabl

Net Income (Loss) Per Share (Tables)	12 Months Ended
	Sep. 30, 2014
Earnings Per Share [Abstract]	'
Basic and Diluted Net Income (Loss) Per Share Attributable to Common Stockholders	'
	Basic and diluted net income (loss) per share attributable to common stockholders was calculated as follows for the years ended September 30, 2014, 2013 and 2012:
		Year Ended September 30,
		2014		2013			2012
	Basic net income (loss) per share attributable to common stockholders:
	Numerator:
	Net income	$	34,438	$	9,627		$	21,399
	Accretion of redeemable convertible preferred stock to redemption value		—		(2,526	)		(5,367	)
	Net income attributable to participating securities		—		(13,670	)		(14,663	)
	Net income (loss) attributable to common stockholders	$	34,438	$	(6,569	)	$	1,369
	Denominator:
	Weighted average common shares outstanding—basic		18,354,791		9,788,039			1,088,784
	Net income (loss) per share attributable to common stockholders—basic	$	1.88	$	(0.67	)	$	1.26
		Year Ended September 30,
		2014		2013			2012
	Diluted net income (loss) per share attributable to common stockholders:
	Numerator:
	Net income	$	34,438	$	9,627		$	21,399
	Accretion of redeemable convertible preferred stock to redemption value		—		(2,526	)		(5,367	)
	Net income attributable to participating securities		—		(13,670	)		(13,225	)
	Net income (loss) attributable to common stockholders—diluted	$	34,438	$	(6,569	)	$	2,807
	Denominator:
	Weighted average common shares outstanding—basic		18,354,791		9,788,039			1,088,784
	Dilutive effect of common stock equivalents		830,437		—			1,386,039
	Weighted average common shares outstanding—diluted		19,185,228		9,788,039			2,474,823
	Net income (loss) per share attributable to common stockholders—diluted	$	1.8	$	(0.67	)	$	1.13

Commitments_and_Contingencies_

Commitments and Contingencies (Tables)	12 Months Ended
	Sep. 30, 2014
Commitments and Contingencies Disclosure [Abstract]	'
Future Minimum Lease Payments for Operating Leases	'
	Future minimum lease payments for operating leases as of September 30, 2014 are as follows:
	Year ending September 30,
	2015	$	946
	2016		972
	2017		999
	2018		1,027
	Total	$	3,944

Income_Taxes_Tables

Income Taxes (Tables)	12 Months Ended
	Sep. 30, 2014
Income Tax Disclosure [Abstract]	'
Summary of provisions for Income Taxes	'
	During the year ended September 30, 2014, the Company recorded a provision for income taxes as follows:
	Current tax expense:
	Federal	$	—
	State		151
	Deferred tax benefit:
	Federal		(13,048	)
	State		(2,273	)
	Total tax benefit	$	(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:
		Year Ended September 30,
		2014			2013			2012
	Federal statutory income tax rate		35	%		34	%		34	%
	State taxes, net of federal benefit		5.5			5.5			5.4
	Federal research and development tax credit		(0.5	)		(2.5	)		(0.2	)
	Change in deferred tax asset valuation allowance		(118.8	)		(51.0	)		(40.1	)
	Change in statutory rate		(2.1	)		—			—
	Other		2.2			14			0.9
	Effective income tax rate		(78.7	)%		0	%		0	%
Net Deferred Tax Assets and Liabilities	'
	Net deferred tax assets as of September 30, 2014 and 2013 consisted of the following:
		September 30,
		2014			2013
	Net operating loss carryforwards	$	2,952		$	8,495
	Tax credit carryforwards		5,920			6,111
	Capitalized research and development expenses		4,756			6,953
	Other temporary differences		1,693			1,333
	Gross deferred tax assets		15,321			22,892
	Valuation allowance		—			(22,892	)
	Net deferred tax assets	$	15,321		$	—
Schedule of Deferred Tax Assets Valuation Allowance	'
	Changes in the valuation allowance for deferred tax assets during the years ended September 30, 2014, 2013 and 2012 were as follows:
		Year Ended September 30,
		2014			2013			2012
	Valuation allowance as of beginning of year	$	22,892		$	27,799		$	36,369
	Decreases recorded as benefit to income tax provision		(22,892	)		(4,907	)		(8,570	)
	Valuation allowance as of end of year	$	—		$	22,892		$	27,799

Selected_Quarterly_Financial_D1

Selected Quarterly Financial Data (unaudited) (Tables)	12 Months Ended
	Sep. 30, 2014
Quarterly Financial Information Disclosure [Abstract]	'
Schedule of Quarterly Financial Information	'
	Quarterly financial information for fiscal 2014 and 2013 is presented in the following table, in thousands, except per share data:
		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	)	$	2.7		$	(0.27	)
	Net income (loss) per share attributable to common shareholders—diluted	$	(0.30	)	$	(0.28	)	$	2.61		$	(0.27	)
		2013 Quarter Ended
		December 31, 2012			March 31, 2013			June 30, 2013			September 30, 2013
	Revenue	$	27,859		$	1,196		$	1,649		$	1,349
	Operating expenses		5,950			5,197			5,827			6,050
	Other income (expense), net		48			252			40			258
	Net income (loss)		21,957			(3,749	)		(4,138	)		(4,443	)
	Net income (loss) per share attributable to common shareholders—basic	$	1.61		$	(2.28	)	$	(0.23	)	$	(0.25	)
	Net income (loss) per share attributable to common shareholders—diluted	$	1.45		$	(2.28	)	$	(0.23	)	$	(0.25	)

Summary_of_Significant_Account3

Summary of Significant Accounting Policies - Additional Information (Detail) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2012
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	436	436	'
Money Market Funds [Member]	'	'	'
Summary of Accounting and Financial Policies [Line Items]	'	'	'
Cash and investment restricted as a collateral for outstanding letter of credit	$436	$436	'
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	'3 months	'	'
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_Account4

Summary of Significant Accounting Policies - Property and Equipment Estimated Useful Lives (Detail)	12 Months Ended
	Sep. 30, 2014
Leasehold Improvements [Member]	'
Property, Plant and Equipment [Line Items]	'
Leasehold improvements useful life	'Shorter of life of lease or estimated useful life
Minimum [Member] | Laboratory and Office Equipment [Member]	'
Property, Plant and Equipment [Line Items]	'
Property plant and equipment useful life	'3 years
Minimum [Member] | Purchased Software [Member]	'
Property, Plant and Equipment [Line Items]	'
Property plant and equipment useful life	'3 years
Minimum [Member] | Computer Equipment [Member]	'
Property, Plant and Equipment [Line Items]	'
Property plant and equipment useful life	'3 years
Maximum [Member] | Laboratory and Office Equipment [Member]	'
Property, Plant and Equipment [Line Items]	'
Property plant and equipment useful life	'5 years
Maximum [Member] | Purchased Software [Member]	'
Property, Plant and Equipment [Line Items]	'
Property plant and equipment useful life	'5 years
Maximum [Member] | Computer Equipment [Member]	'
Property, Plant and Equipment [Line Items]	'
Property plant and equipment useful life	'5 years
Maximum [Member] | Furniture [Member]	'
Property, Plant and Equipment [Line Items]	'
Property plant and equipment useful life	'7 years

Fair_Value_of_Financial_Assets2

Fair Value of Financial Assets and Liabilities - Financial Assets and Liabilities that were Subject to Fair Value Measurement on Recurring Basis (Detail) (USD $)	Sep. 30, 2014	Sep. 30, 2013	Nov. 30, 2010
In Thousands, unless otherwise specified
Assets:	'	'	'
Cash equivalents	$30,239	$7,517	'
Available for sale securities, fair value	101,068	103,324	'
Assets, Fair Value Disclosure, Total	131,307	110,841	'
Liabilities:	'	'	'
Liabilities, Fair Value Disclosure, Total	1,786	1,620	'
Warrant Liability [Member]	'	'	'
Liabilities:	'	'	'
Warrant liability	1,584	1,620	'
Commercial Paper [Member]	'	'	'
Assets:	'	'	'
Available for sale securities, fair value	7,499	10,596	'
Corporate Bonds [Member]	'	'	'
Assets:	'	'	'
Available for sale securities, fair value	88,056	84,755	'
U.S. Agency Bonds [Member]	'	'	'
Assets:	'	'	'
Available for sale securities, fair value	5,513	3,518	'
U.S. Treasury Notes [Member]	'	'	'
Assets:	'	'	'
Available for sale securities, fair value	'	1,005	'
Certificate of Deposit [Member]	'	'	'
Assets:	'	'	'
Available for sale securities, fair value	'	3,450	'
Series 1 Nonconvertible Preferred Stock [Member]	'	'	'
Liabilities:	'	'	'
Warrant liability	1,584	1,620	1,280
Series 1 nonconvertible preferred stock	202	'	'
Level 1 [Member]	'	'	'
Assets:	'	'	'
Cash equivalents	30,239	7,517	'
Assets, Fair Value Disclosure, Total	30,239	8,522	'
Level 1 [Member] | U.S. Treasury Notes [Member]	'	'	'
Assets:	'	'	'
Available for sale securities, fair value	'	1,005	'
Level 2 [Member]	'	'	'
Assets:	'	'	'
Assets, Fair Value Disclosure, Total	101,068	102,319	'
Level 2 [Member] | Commercial Paper [Member]	'	'	'
Assets:	'	'	'
Available for sale securities, fair value	7,499	10,596	'
Level 2 [Member] | Corporate Bonds [Member]	'	'	'
Assets:	'	'	'
Available for sale securities, fair value	88,056	84,755	'
Level 2 [Member] | U.S. Agency Bonds [Member]	'	'	'
Assets:	'	'	'
Available for sale securities, fair value	5,513	3,518	'
Level 2 [Member] | Certificate of Deposit [Member]	'	'	'
Assets:	'	'	'
Available for sale securities, fair value	'	3,450	'
Level 3 [Member]	'	'	'
Liabilities:	'	'	'
Liabilities, Fair Value Disclosure, Total	1,786	1,620	'
Level 3 [Member] | Warrant Liability [Member]	'	'	'
Liabilities:	'	'	'
Warrant liability	1,584	1,620	'
Level 3 [Member] | Series 1 Nonconvertible Preferred Stock [Member]	'	'	'
Liabilities:	'	'	'
Series 1 nonconvertible preferred stock	$202	'	'

Fair_Value_of_Financial_Assets3

Fair Value of Financial Assets and Liabilities - Additional Information (Detail) (USD $)	12 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2012
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
Series 1 nonconvertible preferred stock issued	1,584,000	1,620,000	'
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	$202,000	'	'

Fair_Value_of_Financial_Assets4

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])	12 Months Ended
	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014
		Series 1 Nonconvertible Preferred Stock [Member]	Minimum [Member]	Minimum [Member]	Maximum [Member]	Maximum [Member]
				Series 1 Nonconvertible Preferred Stock [Member]		Series 1 Nonconvertible Preferred Stock [Member]
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]	'	'	'	'	'	'
Probabilities of payout	'	'	25.00%	10.00%	90.00%	90.00%
Periods in which payout is expected to occur, beginning	'2014	'2015	'	'	'	'
Periods in which payout is expected to occur, ending	'2018	'2016	'	'	'	'
Discount rate	4.25%	4.25%	'	'	'	'

Fair_Value_of_Financial_Assets5

Fair Value of Financial Assets and Liabilities - Rollforward of Aggregate Fair Values of Warrants (Detail) (Warrant Liability [Member], USD $)	12 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2012
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]	'	'	'
Beginning Balance	$1,620	$2,001	$1,993
Warrants exercised	-206	'	'
Warrants expired	'	-20	-8
Increase in fair value	166	'	19
Decrease in fair value	'	-361	-3
Ending Balance	1,786	1,620	2,001
Series 1 Nonconvertible Preferred Stock [Member]	'	'	'
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]	'	'	'
Series 1 nonconvertible preferred stock issued	$206	'	'

Marketable_Securities_Fair_Val

Marketable Securities - Fair Value of Available-for-Sale Marketable Securities by Type of Security (Detail) (USD $)	Sep. 30, 2014	Sep. 30, 2013
In Thousands, unless otherwise specified
Schedule of Available-for-sale Securities [Line Items]	'	'
Amortized Cost	$101,168	$103,326
Gross Unrealized Gains	14	24
Gross Unrealized Losses	-114	-26
Fair Value	101,068	103,324
Commercial Paper [Member]	'	'
Schedule of Available-for-sale Securities [Line Items]	'	'
Amortized Cost	7,499	10,596
Fair Value	7,499	10,596
Corporate Bonds [Member]	'	'
Schedule of Available-for-sale Securities [Line Items]	'	'
Amortized Cost	88,156	84,757
Gross Unrealized Gains	14	23
Gross Unrealized Losses	-114	-25
Fair Value	88,056	84,755
U.S. Agency Bonds [Member]	'	'
Schedule of Available-for-sale Securities [Line Items]	'	'
Amortized Cost	5,513	3,519
Gross Unrealized Losses	'	-1
Fair Value	5,513	3,518
Certificate of Deposit [Member]	'	'
Schedule of Available-for-sale Securities [Line Items]	'	'
Amortized Cost	'	3,450
Fair Value	'	3,450
U.S. Treasury Notes [Member]	'	'
Schedule of Available-for-sale Securities [Line Items]	'	'
Amortized Cost	'	1,004
Gross Unrealized Gains	'	1
Fair Value	'	$1,005

Marketable_Securities_Addition

Marketable Securities - Additional Information (Detail) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013
Schedule of Available-for-sale Securities [Line Items]	'	'
Marketable securities maturing in greater than one year, aggregate fair value	41,003	10,703
Short Term Marketable Securities [Member]	'	'
Schedule of Available-for-sale Securities [Line Items]	'	'
Maturity period of the marketable securities	'Within one year	'Within one year
Corporate Bond Securities [Member]	'	'
Schedule of Available-for-sale Securities [Line Items]	'	'
Maturity period of the marketable securities	'Within three years	'Within two years
U.S. Agency Bonds [Member]	'	'
Schedule of Available-for-sale Securities [Line Items]	'	'
Maturity period of the marketable securities	'Within three years	'
US Treasury Notes Securities [Member]	'	'
Schedule of Available-for-sale Securities [Line Items]	'	'
Maturity period of the marketable securities	'	'Within two years

Property_and_Equipment_Schedul

Property and Equipment - Schedule of Property and Equipment (Detail) (USD $)	Sep. 30, 2014	Sep. 30, 2013
In Thousands, unless otherwise specified
Property, Plant and Equipment [Line Items]	'	'
Property and equipment	$5,938	$5,458
Less: Accumulated depreciation and amortization	-4,135	-4,337
Property and equipment, net	1,803	1,121
Laboratory and Office Equipment [Member]	'	'
Property, Plant and Equipment [Line Items]	'	'
Property and equipment	4,829	4,395
Leasehold Improvements [Member]	'	'
Property, Plant and Equipment [Line Items]	'	'
Property and equipment	300	272
Purchased Software [Member]	'	'
Property, Plant and Equipment [Line Items]	'	'
Property and equipment	414	438
Computer Equipment [Member]	'	'
Property, Plant and Equipment [Line Items]	'	'
Property and equipment	111	90
Furniture [Member]	'	'
Property, Plant and Equipment [Line Items]	'	'
Property and equipment	$284	$263

Property_and_Equipment_Additio

Property and Equipment - Additional Information (Detail) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2012
Property, Plant and Equipment [Abstract]	'	'	'
Depreciation and amortization expense	$352	$221	$172
Cost of assets sold	554	420	273
Gain of assets sold	$3	$100	$63

Accrued_Expenses_and_Other_Lon2

Accrued Expenses and Other Long-Term Liabilities - Accrued Expenses (Current) and Other Long-Term Liabilities (Detail) (USD $)	Sep. 30, 2014	Sep. 30, 2013
In Thousands, unless otherwise specified
Accrued expenses:	'	'
Accrued payroll and related expenses	$1,275	$1,041
Accrued preclinical and clinical expenses	493	'
Accrued vendor manufacturing	116	989
Accrued professional fees	436	378
Accrued third-party license fee	240	240
Accrued other	312	387
Accrued expenses	2,872	3,035
Other long-term liabilities:	'	'
Accrued rent expense	153	127
Present value of accrued third-party license fee	'	184
Asset retirement obligation	76	48
Other long-term liabilities	$229	$359

Collaboration_Agreements_Addit

Collaboration Agreements - Additional Information (Detail) (USD $)

0 Months Ended

3 Months Ended

12 Months Ended

0 Months Ended

12 Months Ended

0 Months Ended

12 Months Ended

0 Months Ended

12 Months Ended

0 Months Ended

12 Months Ended

0 Months Ended

Sep. 30, 2012

Sep. 30, 2014

Sep. 30, 2013

Jun. 30, 2014

Sep. 30, 2014

Sep. 30, 2014

Sep. 30, 2014

Sep. 30, 2014

Sep. 30, 2014

Sep. 30, 2014

Sep. 30, 2013

Sep. 30, 2014

Sep. 30, 2014

Sep. 30, 2013

Sep. 30, 2012

Feb. 16, 2012

Sep. 30, 2013

Feb. 16, 2012

Feb. 16, 2012

Sep. 30, 2014

Sep. 30, 2013

Sep. 30, 2012

Aug. 31, 2013

Sep. 30, 2011

Sep. 30, 2014

Sep. 30, 2011

Sep. 30, 2011

Sep. 30, 2011

AbbVie [Member]

AbbVie [Member]

AbbVie [Member]

AbbVie [Member]

AbbVie [Member]

AbbVie [Member]

AbbVie [Member]

AbbVie [Member]

AbbVie [Member]

Novartis [Member]

Novartis [Member]

Novartis [Member]

Novartis [Member]

Novartis [Member]

Novartis [Member]

Novartis [Member]

National Institutes of Health, National Institute of Allergy and Infectious Diseases [Member]

National Institutes of Health, National Institute of Allergy and Infectious Diseases [Member]

National Institutes of Health, National Institute of Allergy and Infectious Diseases [Member]

National Institutes of Health, National Institute of Allergy and Infectious Diseases [Member]

National Institutes of Health, National Institute of Allergy and Infectious Diseases [Member]

National Institutes of Health, National Institute of Allergy and Infectious Diseases [Member]

National Institutes of Health, National Institute of Allergy and Infectious Diseases [Member]

National Institutes of Health, National Institute of Allergy and Infectious Diseases [Member]

National Institutes of Health, National Institute of Allergy and Infectious Diseases [Member]

Paritaprevir 3-DAA Regimen [Member]

Paritaprevir 2-DAA Regimen [Member]

Abt 493 2-DAA Regimen [Member]

Abt 493 3-DAA Regimen [Member]

Milestone Payments [Member]

Milestone Payments [Member]

Milestone Payments [Member]

Quality Assurance and Testing [Member]

Phase 1 Clinical Trial [Member]

Research Contracts [Member]

Maximum [Member]

Initial [Member]

Initial [Member]

Maximum [Member]

Maximum [Member]

Maximum [Member]

Additional Funding Agreement Terms [Member]

Research Contracts [Member]

Renewals

Initial [Member]

Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Collaboration agreement date

'

'

'

'

27-Nov-06

'

'

'

'

'

'

'

16-Feb-12

'

'

'

'

'

'

30-Sep-11

'

'

'

'

'

'

'

'

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

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Delivering period under the AbbVie Agreement

'

'

'

'

'3 years

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Milestone revenue payments received

$0

'

'

$40,000,000

$40,000,000

'

'

'

'

$155,000,000

$15,000,000

'

'

$12,675,000

$35,567,000

'

$11,000,000

'

'

'

'

'

'

'

'

'

'

'

Proceed received to fund research activities and preferred stock financing

'

'

'

'

'

'

'

'

'

'

160,000,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Expected proceed from milestone payment

'

'

'

'

'

'

'

'

'

'

'

80,000,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Percentage of net sales to be allocated

'

'

'

'

'

30.00%

45.00%

50.00%

33.33%

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Agreement continuation period

'

'

'

'

'10 years

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Expected nonrefundable upfront fee and reimbursement expense

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

34,442,000

'

'

'

'

'

'

'

'

'

'

'

'

Funding related to research and development

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

2,700,000

23,500,000

'

'

9,200,000

'

'

'

'

'

Research funding period

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'18 months

'

'

'

'

'

'

'

'

'

'

Amount attributable to license fees

'

'

'

'

'

'

'

'

'

'

'

'

'

10,894,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Amount attributable to the performance of research service

'

'

'

'

'

'

'

'

'

'

'

'

'

1,781,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Awarded contract for development, amount

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

14,300,000

'

'

42,700,000

42,700,000

Awarded contract for development, Contract period

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'30 months

'

'

'5 years

'

Expiration date

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

30-Mar-14

'

'

'

Awarded contract for development, number of extension option

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

6

'

'

Extended expiration date

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'September 30, 2016

'

'

'

'

'

'

'

'

Revenue from grants

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

7,741,000

4,378,000

6,139,000

'

'

'

'

'

'

Revenue invoiced but unpaid

'

1,724,000

808,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

1,724,000

258,000

1,049,000

'

'

'

'

'

'

Revenue unpaid and included in unbilled receivables

'

$2,770,000

$784,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

$2,770,000

$784,000

$1,668,000

'

'

'

'

'

'

Stockholders_Equity_Additional

Stockholders' Equity - Additional Information (Detail) (USD $)	0 Months Ended		12 Months Ended					12 Months Ended		0 Months Ended
In Thousands, except Share data, unless otherwise specified	Mar. 26, 2013	Mar. 01, 2013	Sep. 30, 2013	Sep. 30, 2014	Mar. 31, 2013	Mar. 26, 2013	Feb. 29, 2012	Sep. 30, 2014	Sep. 30, 2013	Mar. 26, 2013
								Series 1 Nonconvertible Preferred Stock [Member]	Series 1 Nonconvertible Preferred Stock [Member]	Conversion of Redeemable Convertible Preferred Stock and Convertible Preferred Stock [Member]
Changes In Equity And Comprehensive Income Line Items [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	'	'	'	'	'	'	'	'	'
Net proceeds from initial public offering	$59,892	'	$59,892	'	'	'	'	'	'	'
Shares issued, price per share	'	'	'	'	'	$14	'	'	'	'
Shares of common stock issued upon conversion of preferred stock	'	'	'	'	'	'	'	'	'	11,656,875
Preferred Shares authorized	'	'	'	'	'	'	'	1,999,989	'	'
Par value of outstanding convertible preferred stock	'	'	'	'	'	'	'	$0.01	'	'
Preferred shares issued	'	'	'	'	'	'	'	223,153	0	'
Preferred shares outstanding	'	'	'	'	'	'	'	223,153	0	'
Per share value adjusted for stock dividend	'	'	'	'	'	'	'	$1	'	'
Preferred stock redemption price per share	'	'	'	'	'	'	'	$1	'	'
Redemption period	'	'	'	'	'	'	'	'60 days	'	'
Aggregate liquidation preference	'	'	'	'	'	'	'	'	$2,000	'

Preferred_Stock_Warrants_Addit

Preferred Stock Warrants - Additional Information (Detail) (USD $)	0 Months Ended	12 Months Ended
In Thousands, except Share data, unless otherwise specified	Feb. 05, 2014	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2011	Nov. 30, 2010
Series E Preferred Stock [Member]	'	'	'	'	'	'
Class of Stock [Line Items]	'	'	'	'	'	'
Warrant for the purchase of series E preferred stock outstanding	'	'	'	12,500	341,556	'
Warrant for the purchase of shares expired	'	'	12,500	329,056	'	'
Warrants expired	'	'	12,500	'	'	'
Change in fair value of the warrants	'	'	'	$19	'	'
Income expense related to warrant expiration	'	'	20	8	'	'
Warrant fair value	'	'	'	20	'	'
Series 1 Nonconvertible Preferred Stock [Member]	'	'	'	'	'	'
Class of Stock [Line Items]	'	'	'	'	'	'
Warrant for the purchase of series E preferred stock outstanding	'	1,774,581	1,999,989	1,999,989	1,999,989	'
Change in fair value of the warrants	'	166	-361	16	'	'
Number of shares issuable upon exercise of the warrants	'	'	'	'	'	1,999,989
Warrant expiration date	'	4-Oct-17	'	'	'	'
Fair value of warrants	'	1,584	1,620	'	'	1,280
Warrant exercised	225,408	'	'	'	'	'
Warrants issuance	223,153	'	'	'	'	'
Fair value of the Series 1 nonconvertible preferred stock	'	$202	'	'	'	'

Preferred_Stock_Warrants_Summa

Preferred Stock Warrants - Summary of Warrant Activity (Detail) (USD $)	12 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2012
Series E Preferred Stock [Member]	'	'	'
Preferred Stock And Warrant [Line Items]	'	'	'
Beginning Balance	'	12,500	341,556
Granted	0	0	0
Expired	'	-12,500	-329,056
Ending Balance	'	'	12,500
Weighted Average Exercise Price Outstanding, Beginning Balance	'	$2.51	$2.51
Weighted Average Exercise Price Outstanding, Ending Balance	'	'	$2.51
Series 1 Nonconvertible Preferred Stock [Member]	'	'	'
Preferred Stock And Warrant [Line Items]	'	'	'
Beginning Balance	1,999,989	1,999,989	1,999,989
Granted	0	0	0
Exercised	-225,408	'	'
Ending Balance	1,774,581	1,999,989	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

StockBased_Awards_Additional_I

Stock-Based Awards - Additional Information (Detail) (USD $)

12 Months Ended

1 Months Ended

12 Months Ended

0 Months Ended

12 Months Ended

In Thousands, except Share data, unless otherwise specified

Sep. 30, 2014

Sep. 30, 2013

Sep. 30, 2012

Jan. 03, 2013

Mar. 31, 2013

Sep. 30, 2014

Sep. 30, 2013

Oct. 01, 2013

Sep. 30, 2014

Sep. 30, 2014

Sep. 30, 2014

Sep. 30, 2014

Sep. 30, 2014

Executive Officer [Member]

Executive Officer [Member]

Executive Officer [Member]

2012 Equity Incentive Plan [Member]

2012 Equity Incentive Plan [Member]

2012 Equity Incentive Plan [Member]

2012 Equity Incentive Plan [Member]

2012 Equity Incentive Plan [Member]

2012 Equity Incentive Plan [Member]

Executive Officer [Member]

Executive Officer [Member]

Board of Directors [Member]

Board of Directors [Member]

Minimum [Member]

Maximum [Member]

Minimum [Member]

Maximum [Member]

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

'

'

'

'

'

'

'

'

'

'

'

'

'

Percentage of potential common stock shares to be issued

'

'

'

'

'

'

'

'

3.00%

'

'

'

'

Potential number of common stock shares to be issued

'

'

'

'

'

'

'

538,102

2,088,167

'

'

'

'

Shares available for future grant

'

'

'

'

'

'

'

'

412,943

'

'

'

'

Options granted, vesting period

'

'

'

'

'

'

'

'

'4 years

'1 year

'4 years

'2 years

'3 years

Options granted, expiration period

'

'

'

'

'

'

'

'

'10 years

'

'

'

'

Common stock reserved

'

'

'

185,614

'

'

'

'

'

'

'

'

'

Shares issued under the ESPP

0

'

'

'

'

'

'

'

'

'

'

'

'

Period for service based award

'4 years

'

'

'

'

'

'

'

'

'

'

'

'

Options granted to executives

488,570

'

'

'

167,052

'

'

'

'

'

'

'

'

Fair value of options at the grant date

'

'

'

'

$2,479

'

'

'

'

'

'

'

'

Stock based compensation, expenses

'

'

'

'

'

206

0

'

'

'

'

'

'

Aggregate intrinsic value of stock options exercised

3,219

7,574

606

'

'

'

'

'

'

'

'

'

'

Cash proceeds from exercise of stock options

1,054

559

141

'

'

'

'

'

'

'

'

'

'

Weighted average grant date fair value of option granted

$19.98

$9.16

$7.79

'

'

'

'

'

'

'

'

'

'

Aggregate of unrecognized stock-based compensation cost

$8,467

'

'

'

'

'

'

'

'

'

'

'

'

Weighted average recognition period

'3 years 1 month 6 days

'

'

'

'

'

'

'

'

'

'

'

'

StockBased_Awards_Data_Used_to

Stock-Based Awards - Data Used to Determine Value of Stock Option Grants, Presented on Weighted Average Basis (Detail)	12 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2012
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]	'	'	'
Risk-free interest rate	1.89%	1.05%	0.93%
Expected term (in years)	'6 years 22 days	'6 years 1 month 2 days	'6 years
Expected volatility	75.00%	73.00%	78.00%
Expected dividend yield	0.00%	0.00%	0.00%

StockBased_Awards_Stock_Option

Stock-Based Awards - Stock Option Activity (Detail) (USD $)	12 Months Ended
In Thousands, except Share data, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013
Shares Issuable Under Options	'	'
Outstanding as of beginning of period	1,583,031	'
Granted	488,570	'
Exercised	-664,793	'
Forfeited	-16,906	'
Expired	-465	'
Outstanding as of end of period	1,389,437	1,583,031
Options vested and expected to vest as of end of period	1,209,316	'
Options exercisable as of end of period	708,010	'
Weighted Average Exercise Price	'	'
Outstanding as of beginning of period	$5.15	'
Granted	$29.83	'
Exercised	$1.61	'
Forfeited	$16.64	'
Expired	$0.73	'
Outstanding as of ending balance	$15.39	$5.15
Options vested and expected to vest as of end of period	$15.47	'
Options exercisable as of end of period	$7.37	'
Weighted Average Remaining Contractual Term (In years)	'	'
Outstanding as of end of period	'7 years 2 months 12 days	'5 years
Options vested and expected to vest as of end period	'7 years	'
Options exercisable as of end of period	'5 years 7 months 6 days	'
Aggregate Intrinsic Value	'	'
Outstanding as of beginning of period	$28,133	'
Outstanding as of end of period	33,573	28,133
Options vested and expected to vest as of end of period	29,126	'
Options exercisable as of end of period	$22,767	'

StockBased_Awards_StockBased_C

Stock-Based Awards - Stock-Based Compensation Expense (Detail) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2012
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]	'	'	'
Stock-based compensation expense	$2,682	$1,063	$424
Research and Development [Member]	'	'	'
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]	'	'	'
Stock-based compensation expense	762	393	126
General and Administrative [Member]	'	'	'
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]	'	'	'
Stock-based compensation expense	$1,920	$670	$298

Net_Income_Loss_Per_Share_Basi

Net Income (Loss) Per Share - Basic and Diluted Net Income (Loss) Per Share Attributable to Common Stockholders (Detail) (USD $)	3 Months Ended								12 Months Ended
In Thousands, except Share data, unless otherwise specified	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2012
Basic net income (loss) per share attributable to common stockholders:	'	'	'	'	'	'	'	'	'	'	'
Net income	($5,042)	$50,053	($5,203)	($5,370)	($4,443)	($4,138)	($3,749)	$21,957	$34,438	$9,627	$21,399
Accretion of redeemable convertible preferred stock to redemption value	'	'	'	'	'	'	'	'	'	-2,526	-5,367
Net income attributable to participating securities	'	'	'	'	'	'	'	'	'	-13,670	-14,663
Net income (loss) attributable to common stockholders	'	'	'	'	'	'	'	'	34,438	-6,569	1,369
Weighted average common shares outstanding-basic	'	'	'	'	'	'	'	'	18,354,791	9,788,039	1,088,784
Net income (loss) per share attributable to common stockholders-basic	($0.27)	$2.70	($0.28)	($0.30)	($0.25)	($0.23)	($2.28)	$1.61	$1.88	($0.67)	$1.26
Diluted net income (loss) per share attributable to common stockholders:	'	'	'	'	'	'	'	'	'	'	'
Net income	-5,042	50,053	-5,203	-5,370	-4,443	-4,138	-3,749	21,957	34,438	9,627	21,399
Accretion of redeemable convertible preferred stock to redemption value	'	'	'	'	'	'	'	'	'	-2,526	-5,367
Net income attributable to participating securities	'	'	'	'	'	'	'	'	'	-13,670	-13,225
Net income (loss) attributable to common stockholders-diluted	'	'	'	'	'	'	'	'	$34,438	($6,569)	$2,807
Weighted average common shares outstanding-basic	'	'	'	'	'	'	'	'	18,354,791	9,788,039	1,088,784
Dilutive effect of common stock equivalents	'	'	'	'	'	'	'	'	830,437	'	1,386,039
Weighted average common shares outstanding-diluted	'	'	'	'	'	'	'	'	19,185,228	9,788,039	2,474,823
Net income (loss) per share attributable to common stockholders-diluted	($0.27)	$2.61	($0.28)	($0.30)	($0.25)	($0.23)	($2.28)	$1.45	$1.80	($0.67)	$1.13

Net_Income_Loss_Per_Share_Addi

Net Income (Loss) Per Share - Additional Information (Detail) (Stock Option [Member])	12 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2012
Stock Option [Member]	'	'	'
Dilutive Securities Included And Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]	'	'	'
Shares excluded from the computation of diluted net income per share	330,430	1,713,313	33,359

Commitments_and_Contingencies_1

Commitments and Contingencies - Additional Information (Detail) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2012
Commitments And Contingencies [Line Items]	'	'	'
Lease for new office space Duration	'7 years	'	'
Rent expense	$948	$948	$948
Outstanding letter of credit	436	'	'
Restricted cash	436	436	'
Upfront license fees payable	'	'	350
License expense	'	'	895
Maintenance fees	'	'	105
One-time fee	'	'	50
License agreement, recorded liability	6,761	6,505	'
License agreement, recorded liability paid	1,874	1,481	'
License agreement, recorded liability included in accrued expenses	2,872	3,035	'
Company's obligation to pay	'	5,000	'
Payment for license agreement	'	500	'
License Agreement Terms [Member]	'	'	'
Commitments And Contingencies [Line Items]	'	'	'
License agreement, recorded liability	'	'	995
License agreement, recorded liability paid	250	350	'
License agreement, recorded liability included in accrued expenses	192	'	'
First Anniversary [Member]	'	'	'
Commitments And Contingencies [Line Items]	'	'	'
License expense	'	'	250
Second Anniversary [Member]	'	'	'
Commitments And Contingencies [Line Items]	'	'	'
License expense	'	'	250
Third Anniversary [Member]	'	'	'
Commitments And Contingencies [Line Items]	'	'	'
License expense	'	'	$200

Commitments_and_Contingencies_2

Commitments and Contingencies - Future Minimum Lease Payments for Operating Leases (Detail) (USD $)	Sep. 30, 2014
In Thousands, unless otherwise specified
Commitments and Contingencies Disclosure [Abstract]	'
2015	$946
2016	972
2017	999
2018	1,027
Total	$3,944

Income_Taxes_Summary_of_provis

Income Taxes - Summary of provisions for Income Taxes (Detail) (USD $)	3 Months Ended		9 Months Ended	12 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2014	Jun. 30, 2014	Jun. 30, 2014	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2012
Current tax expense:	'	'	'	'	'	'
Federal	'	'	'	$0	'	'
State	'	'	'	151	'	'
Deferred tax benefit:	'	'	'	'	'	'
Federal	'	'	'	-13,048	'	'
State	'	'	'	-2,273	'	'
Total tax benefit	$48	$15,122	$15,122	($15,170)	$0	$0

Income_Taxes_Additional_Inform

Income Taxes - Additional Information (Detail) (USD $)	0 Months Ended	3 Months Ended		9 Months Ended	12 Months Ended
	Sep. 30, 2012	Sep. 30, 2014	Jun. 30, 2014	Jun. 30, 2014	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2012
Income Tax [Line Items]	'	'	'	'	'	'	'
Income tax expense (benefit)	'	$48,000	$15,122,000	$15,122,000	($15,170,000)	$0	$0
Income before income taxes	'	'	'	'	19,268,000	9,627,000	21,399,000
Effective income tax rate	'	'	'	'	-78.70%	0.00%	0.00%
Federal statutory income tax rate	'	'	'	'	35.00%	34.00%	34.00%
Decreases recorded as benefit to income tax provision	'	'	'	22,892,000	22,892,000	4,907,000	8,570,000
Milestone revenue payments received	0	'	'	'	'	'	'
Change in estimate regarding future years' income	'	'	'	15,333,000	'	'	'
Released to income as deferred tax assets	'	'	7,559,000	7,559,000	'	'	'
Unrecognized tax benefits	0	0	'	'	0	0	0
AbbVie [Member]	'	'	'	'	'	'	'
Income Tax [Line Items]	'	'	'	'	'	'	'
Milestone revenue payments received	'	'	40,000,000	'	40,000,000	'	'
Federal[Member]	'	'	'	'	'	'	'
Income Tax [Line Items]	'	'	'	'	'	'	'
Net operating loss carryforwards	'	8,433,000	'	'	8,433,000	'	'
Net operating loss carryforwards begin to expire	'	'	'	'	'2018	'	'
Research and development tax credit carryforwards	'	4,481,000	'	'	4,481,000	'	'
Research and development tax credit carryforwards begin to expire	'	'	'	'	'2021	'	'
State[Member]	'	'	'	'	'	'	'
Income Tax [Line Items]	'	'	'	'	'	'	'
Net operating loss carryforwards	'	0	'	'	0	'	'
Net operating loss carryforwards begin to expire	'	'	'	'	'2018	'	'
Research and development tax credit carryforwards	'	$2,214,000	'	'	$2,214,000	'	'
Research and development tax credit carryforwards begin to expire	'	'	'	'	'2018	'	'

Income_Taxes_Reconciliation_of

Income Taxes - Reconciliation of Income Tax Provision at Federal Statutory Income Tax Rate and Effective Tax Rate (Detail)	12 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2012
Income Tax Disclosure [Abstract]	'	'	'
Federal statutory income tax rate	35.00%	34.00%	34.00%
State taxes, net of federal benefit	5.50%	5.50%	5.40%
Federal research and development tax credit	-0.50%	-2.50%	-0.20%
Change in deferred tax asset valuation allowance	-118.80%	-51.00%	-40.10%
Change in statutory rate	-2.10%	'	'
Other	2.20%	14.00%	0.90%
Effective income tax rate	-78.70%	0.00%	0.00%

Income_Taxes_Net_Deferred_Tax_

Income Taxes - Net Deferred Tax Assets and Liabilities (Detail) (USD $)	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2011
In Thousands, unless otherwise specified
Income Tax Disclosure [Abstract]	'	'	'	'
Net operating loss carryforwards	$2,952	$8,495	'	'
Tax credit carryforwards	5,920	6,111	'	'
Capitalized research and development expenses	4,756	6,953	'	'
Other temporary differences	1,693	1,333	'	'
Gross deferred tax assets	15,321	22,892	'	'
Valuation allowance	'	-22,892	-27,799	-36,369
Net deferred tax assets	$15,321	'	'	'

Income_Taxes_Schedule_of_Defer

Income Taxes - Schedule of Deferred Tax Assets Valuation Allowance (Detail) (USD $)	9 Months Ended	12 Months Ended
In Thousands, unless otherwise specified	Jun. 30, 2014	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2012
Income Tax Disclosure [Abstract]	'	'	'	'
Valuation allowance as of beginning of year	$22,892	$22,892	$27,799	$36,369
Decreases recorded as benefit to income tax provision	-22,892	-22,892	-4,907	-8,570
Valuation allowance as of end of year	'	'	$22,892	$27,799

401k_Plan_Additional_Informati

401(k) Plan - Additional Information (Detail) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2012
Defined Benefit Plan Disclosure [Line Items]	'	'	'
Benefits charged to operating expenses	$180	$90	$84
Maximum [Member]	'	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'	'
Percentage of annual contribution	3.00%	'	'
Annual base salary of employee	8	'	'
Maximum [Member] | Scenario, Previously Reported [Member]	'	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'	'
Percentage of annual contribution	2.00%	'	'
Annual base salary of employee	$4	'	'

Selected_Quarterly_Financial_D2

Selected Quarterly Financial Data (Unaudited) - Schedule of Quarterly Financial Information (Detail) (USD $)	3 Months Ended								9 Months Ended	12 Months Ended
In Thousands, except Per Share data, unless otherwise specified	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Jun. 30, 2014	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2012
Quarterly Financial Information Disclosure [Abstract]	'	'	'	'	'	'	'	'	'	'	'	'
Revenue	$2,637	$42,051	$2,160	$893	$1,349	$1,649	$1,196	$27,859	'	$47,741	$32,053	$41,706
Operating expenses	7,963	7,156	7,287	6,350	6,050	5,827	5,197	5,950	'	28,756	23,024	20,417
Other income (expense), net	236	36	-76	87	258	40	252	48	'	'	'	'
Income tax benefit	48	15,122	'	'	'	'	'	'	15,122	-15,170	0	0
Net income (loss)	($5,042)	$50,053	($5,203)	($5,370)	($4,443)	($4,138)	($3,749)	$21,957	'	$34,438	$9,627	$21,399
Net income (loss) per share attributable to common shareholders-basic	($0.27)	$2.70	($0.28)	($0.30)	($0.25)	($0.23)	($2.28)	$1.61	'	$1.88	($0.67)	$1.26
Net income (loss) per share attributable to common shareholders-diluted	($0.27)	$2.61	($0.28)	($0.30)	($0.25)	($0.23)	($2.28)	$1.45	'	$1.80	($0.67)	$1.13