Eledon Pharmaceuticals (ELDN) 10-K 26 Mar 15 2014 FY Annual report Financial data

Document_and_Entity_Informatio

Document and Entity Information (USD $)	12 Months Ended
	Dec. 31, 2014	Mar. 15, 2015	Jun. 30, 2014
Document And Entity Information [Abstract]
Document Type	10-K
Amendment Flag	FALSE
Document Period End Date	31-Dec-14
Document Fiscal Year Focus	2014
Document Fiscal Period Focus	FY
Trading Symbol	TKAI
Entity Registrant Name	TOKAI PHARMACEUTICALS INC
Entity Central Index Key	1404281
Current Fiscal Year End Date	-19
Entity Well-known Seasoned Issuer	No
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No
Entity Filer Category	Non-accelerated Filer
Entity Common Stock, Shares Outstanding		22,382,340
Entity Public Float			$0

Consolidated_Balance_Sheets

Consolidated Balance Sheets (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Current assets:
Cash and cash equivalents	$105,256	$31,753
Prepaid expenses and other current assets	2,255	425
Total current assets	107,511	32,178
Property and equipment, net	33	29
Deferred offering costs		30
Restricted cash	200	50
Total assets	107,744	32,287
Current liabilities:
Accounts payable	765	5
Accrued expenses	3,478	2,204
Total current liabilities	4,243	2,209
Total liabilities	4,243	2,209
Commitments and contingencies
Redeemable convertible preferred stock (Series A, B-1, B-2, C, D-1, D-2, D-3 and E), $0.001 par value; no shares and 155,586,141 shares authorized at December 31, 2014 and 2013, respectively; no shares and 155,586,141 shares issued and outstanding at December 31, 2014 and 2013, respectively		85,345
Stockholders' equity (deficit):
Preferred stock, $0.001 par value; 5,000,000 and no shares authorized at December 31, 2014 and 2013, respectively; no shares issued or outstanding at December 31, 2014 and 2013, respectively	0	0
Common stock, $0.001 par value; 200,000,000 and 173,018,331 shares authorized at December 31, 2014 and 2013, respectively, and 22,382,340 and 493,292 shares issued and outstanding at December 31, 2014 and 2013, respectively	22
Additional paid-in capital	189,830	7,788
Accumulated deficit	-86,351	-63,055
Total stockholders' equity (deficit)	103,501	-55,267
Total liabilities, redeemable convertible preferred stock and stockholders' equity (deficit)	$107,744	$32,287

Consolidated_Balance_Sheets_Pa

Consolidated Balance Sheets (Parenthetical) (USD $)	Dec. 31, 2014	Dec. 31, 2013
Statement of Financial Position [Abstract]
Redeemable convertible preferred stock, par value	$0.00	$0.00
Redeemable convertible preferred stock, shares authorized	0	155,586,141
Redeemable convertible preferred stock, shares issued	0	155,586,141
Redeemable convertible preferred stock, shares outstanding	0	155,586,141
Preferred stock, par value	$0.00	$0.00
Preferred stock, shares authorized	5,000,000	0
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value	$0.00	$0.00
Common stock, shares authorized	200,000,000	173,018,331
Common stock, shares issued	22,382,340	493,292
Common stock, shares outstanding	22,382,340	493,292

Consolidated_Statements_of_Ope

Consolidated Statements of Operations and Comprehensive Loss (USD $)	12 Months Ended
In Thousands, except Share data, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Income Statement [Abstract]
Revenue	$0	$0	$0
Operating expenses:
Research and development	14,577	12,201	7,370
General and administrative	8,885	3,548	2,279
Total operating expenses	23,462	15,749	9,649
Loss from operations	-23,462	-15,749	-9,649
Other income	166	24
Net loss and comprehensive loss	-23,296	-15,725	-9,649
Accretion of redeemable convertible preferred stock to redemption value		-94	-34
Net loss attributable to common stockholders	($23,296)	($15,819)	($9,683)
Net loss per share attributable to common stockholders, basic and diluted	($3.60)	($38.02)	($31.09)
Weighted average common shares outstanding, basic and diluted	6,469,289	416,037	311,474

Consolidated_Statements_of_Cha

Consolidated Statements of Changes in Redeemable Convertible Preferred Stock and Stockholders' Equity (Deficit) (USD $)	Total	Series D-3 Redeemable Convertible Preferred Stock [Member]	Series E Redeemable Convertible Preferred Stock [Member]	IPO [Member]	Series A, B-1, B-2, C,D-1, D-2, D-3 and E Redeemable Convertible Preferred Stock [Member]	Series A, B-1, B-2, C,D-1, D-2, D-3 and E Redeemable Convertible Preferred Stock [Member]	Series A, B-1, B-2, C,D-1, D-2, D-3 and E Redeemable Convertible Preferred Stock [Member]	Common Stock [Member]	Common Stock [Member]	Additional Paid-in Capital [Member]	Additional Paid-in Capital [Member]	Additional Paid-in Capital [Member]	Additional Paid-in Capital [Member]	Accumulated Deficit [Member]
In Thousands, except Share data						Series D-3 Redeemable Convertible Preferred Stock [Member]	Series E Redeemable Convertible Preferred Stock [Member]		IPO [Member]		Series D-3 Redeemable Convertible Preferred Stock [Member]	Series E Redeemable Convertible Preferred Stock [Member]	IPO [Member]
Beginning Balance at Dec. 31, 2011	($30,432)				$30,895					$7,249				($37,681)
Beginning Balance, Shares at Dec. 31, 2011					63,997,708			306,817
Issuance of common stock upon exercise of stock options	4									4
Issuance of common stock upon exercise of stock options, Shares								2,843
Stock-based compensation expense	210									210
Conversion of preferred stock to common stock						18,916
Conversion of preferred stock to common stock, Shares						34,696,042
Accretion of redeemable convertible preferred stock to redemption value		-34				34					-34
Net loss	-9,649													-9,649
Issuance of common stock								154,973
Ending Balance at Dec. 31, 2012	-39,901				49,845					7,429				-47,330
Ending Balance, Shares at Dec. 31, 2012					98,693,750			464,633
Issuance of common stock upon exercise of stock options	215									215
Issuance of common stock upon exercise of stock options, Shares								157,804
Stock-based compensation expense	238									238
Conversion of preferred stock to common stock							35,406
Conversion of preferred stock to common stock, Shares							56,892,391
Accretion of redeemable convertible preferred stock to redemption value			-94				94					-94
Net loss	-15,725													-15,725
Repurchase and forfeiture of unvested restricted stock, Shares								-129,145
Ending Balance at Dec. 31, 2013	-55,267				85,345					7,788				-63,055
Ending Balance, Shares at Dec. 31, 2013					155,586,141			493,292
Issuance of common stock upon exercise of stock options	16									16
Issuance of common stock upon exercise of stock options, Shares	8,875							8,875
Stock-based compensation expense	2,108									2,108
Conversion of preferred stock to common stock	85,345				-85,345			15		85,330
Conversion of preferred stock to common stock, Shares					-155,586,141			14,860,173
Issuance costs	-3,334									-3,334
Net loss	-23,296													-23,296
Issuance of common stock				97,929					7				97,922
Issuance of common stock									7,020,000
Ending Balance at Dec. 31, 2014	$103,501							$22		$189,830				($86,351)
Ending Balance, Shares at Dec. 31, 2014								22,382,340

Consolidated_Statements_of_Cha1

Consolidated Statements of Changes in Redeemable Convertible Preferred Stock and Stockholders' Equity (Deficit) (Parenthetical) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Net of issuance costs	$3,304	$30
Series D-3 Redeemable Convertible Preferred Stock [Member]
Net of issuance costs			34
Series E Redeemable Convertible Preferred Stock [Member]
Net of issuance costs		$94

Consolidated_Statements_of_Cas

Consolidated Statements of Cash Flows (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Cash flows from operating activities:
Net loss	($23,296)	($15,725)	($9,649)
Adjustments to reconcile net loss to net cash used in operating activities:
Stock-based compensation expense	2,108	238	210
Depreciation expense	21	10	9
Release of reserve for loan to former advisor	-158
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	-1,830	-190	139
Accounts payable	760	-759	-119
Accrued expenses	1,274	950	77
Net cash used in operating activities	-21,121	-15,476	-9,333
Cash flows from investing activities:
Purchases of property and equipment	-25	-23	-8
Change in restricted cash	-150	-30
Net cash used in investing activities	-175	-53	-8
Cash flows from financing activities:
Proceeds from initial public offering, net of underwriting discounts and commissions	97,929
Payments of initial public offering costs	-3,304	-30
Proceeds from issuance of redeemable convertible preferred stock, net of issuance costs		35,406	18,775
Repayment of notes receivable	158
Proceeds from exercise of common stock options	16	215	4
Net cash provided by financing activities	94,799	35,591	18,779
Net increase in cash and cash equivalents	73,503	20,062	9,438
Cash and cash equivalents at beginning of period	31,753	11,691	2,253
Cash and cash equivalents at end of period	105,256	31,753	11,691
Supplemental disclosure of non-cash investing and financing activities:
Accretion of redeemable convertible preferred stock to redemption value		94	34
Conversion of redeemable convertible preferred stock to common stock	-85,345
Conversion of convertible promissory notes and accrued interest and advance from stockholder to shares of redeemable convertible preferred stock			$141

Nature_of_the_Business_and_Bas

Nature of the Business and Basis of Presentation	12 Months Ended
	Dec. 31, 2014
Accounting Policies [Abstract]
Nature of the Business and Basis of Presentation	1. Nature of the Business and Basis of Presentation
	Tokai Pharmaceuticals, Inc. (the “Company”) was incorporated on March 26, 2004 under the laws of the State of Delaware. The Company is a clinical-stage biopharmaceutical company focused on developing novel proprietary therapies for the treatment of prostate cancer and other hormonally-driven diseases. The Company’s lead drug candidate, galeterone, is a highly selective, multi-targeted, oral small molecule drug candidate. Since its inception, the Company has devoted substantially all of its efforts to research and development, recruiting management, in-licensing technology and raising capital.
	The Company was previously classified as a “development stage entity” in the Accounting Standards Codification and, as such, was required to present inception-to-date information in the Company’s statements of operations and comprehensive loss, redeemable convertible preferred stock and stockholders’ deficit, and cash flows. In June 2014, the Financial Accounting Standards Board (“FASB”) issued an accounting standards update that eliminated the concept of a development stage entity from U.S. generally accepted accounting principles and removed the related incremental reporting requirements. See Note 2 below for additional information on this new standard. The Company elected to early adopt the new standard in 2014. Accordingly, in contrast to the Company’s financial statements and the notes thereto for the year ended December 31, 2013 included in Company’s Registration Statement on Form S-1, as amended, filed with the Securities and Exchange Commission (“SEC”), the financial statements contained in this report do not include inception-to-date information.
	The Company is subject to risks common to companies in the biotechnology industry including, but not limited to, new technological innovations, protection of proprietary technology, dependence on key personnel, compliance with government regulations and the need to obtain additional financing. Galeterone, which is currently under development, and any product candidates that the Company may seek to develop in the future 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.
	There can be no assurance that the Company’s research and development will be successfully completed, that adequate protection for the Company’s intellectual property will be obtained, that any products developed will obtain necessary government regulatory approval or that any approved products will be commercially viable. Even if the Company’s drug development efforts are successful, it is uncertain when, if ever, the Company will generate significant revenue from product sales. The Company operates in an environment of rapid change in technology and substantial competition from pharmaceutical and biotechnology companies. In addition, the Company is dependent upon the services of its employees and consultants.
	The accompanying consolidated financial statements and footnotes include Diotima Pharmaceuticals, Inc. (“Diotima”), a variable interest entity in which the Company had a variable financial interest and was the primary beneficiary but had no ownership interest. In 2010, the Company formed and incorporated Diotima. Diotima operated as a stand-alone company with limited activity through April 2014. In early 2014, the license agreements relating to the Diotima compounds were terminated. Additionally, in April 2014, the board of directors and stockholders of Diotima approved the dissolution of Diotima, and Diotima was dissolved. All significant intercompany balances and transactions between the Company and Diotima have been eliminated in consolidation. See Note 7 for additional information on Diotima.
	On September 22, 2014, the Company completed an initial public offering (“IPO”) of its common stock, and issued and sold 6,480,000 shares of common stock at a public offering price of $15.00 per share, resulting in net proceeds of $87,062 after deducting underwriting discounts and commissions and offering expenses. Upon the closing of the IPO, all outstanding shares of the Company’s redeemable convertible preferred stock automatically converted into 14,860,173 shares of the Company’s common stock. On October 9, 2014, the Company issued and sold an additional 540,000 shares of its common stock at the IPO price of $15.00 per share, pursuant to the underwriters’ partial exercise of their option to purchase additional shares of common stock, resulting in additional net proceeds to the Company of $7,533 after deducting underwriting discounts and commissions (Note 6).
	The Company’s consolidated financial statements have been prepared on the basis of continuity of operations, realization of assets and the satisfaction of liabilities in the ordinary course of business. The Company has incurred losses and negative cash flows from operations since inception. As of December 31, 2014, the Company had an accumulated deficit of $86,351. The Company believes its cash and cash equivalents balance of $105,256 as of December 31, 2014 will be sufficient to fund its anticipated level of operations for at least the next 12 months. The Company’s ability to generate product revenue and operating cash flow will depend heavily on the successful development and eventual commercialization of galeterone and other product candidates that it may develop in the future. If the Company is unable to generate positive cash flows from operations, it may have to seek other sources of capital.

Summary_of_Significant_Account

Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2014
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	2. Summary of Significant Accounting Policies
	Use of Estimates
	The preparation of financial statements in conformity with GAAP requires management to make estimates, assumptions and judgments 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 expenses during the reporting periods. Significant estimates, assumptions and judgments reflected in these consolidated financial statements include, but are not limited to, the accrual of research and development expenses, the valuation of common stock and redeemable convertible preferred stock prior to the Company’s IPO and the valuation of stock-based awards. Estimates are periodically reviewed in light of changes in circumstances, facts and experience. Actual results could differ from the Company’s estimates.
	Cash Equivalents
	The Company considers all short-term, highly liquid investments with original maturities of ninety days or less at date of purchase to be cash equivalents. Cash equivalents, which consist of money market accounts, are stated at fair value.
	Concentration of Credit Risk and of Significant Suppliers
	Financial instruments that potentially expose the Company to concentrations of credit risk consist primarily of cash and cash equivalents. The Company has all cash and cash equivalents 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 is dependent on third-party manufacturers to supply products for research and development activities in its programs. In particular, the Company relies and expects to continue to rely on a small number of manufacturers to supply it with its requirements for the active pharmaceutical ingredients and formulated drugs related to these programs. These programs could be adversely affected by a significant interruption in the supply of active pharmaceutical ingredients and formulated drugs.
	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. Financial assets and liabilities carried at fair value are to be classified and disclosed in one of the following three levels of the fair value hierarchy, of which the first two are considered observable and the last is considered unobservable:
		•		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 of $91,316 and $1,311 as of December 31, 2014 and 2013, respectively, were carried at fair value based on Level 2 inputs. The carrying values of accounts payable and accrued expenses approximate their fair value due to the short-term nature of these liabilities.
	Deferred Offering Costs
	The Company capitalizes certain legal, accounting and other third-party fees that are directly associated with in-process equity financings as other assets until such financings are consummated. After consummation of the equity financing, these costs are recorded in stockholders’ equity (deficit) as a reduction of additional paid-in capital generated as a result of the offering or as a reduction to the carrying value of preferred stock issued. As of December 31, 2013, the Company had recorded $30 of deferred offering costs, included in other assets in the accompanying consolidated balance sheet in contemplation of the Company’s IPO, which closed in September 2014. The Company has no deferred offering costs as of December 31, 2014.
	Property and Equipment
	Property and equipment are stated at cost less accumulated depreciation. Depreciation expense is recognized using the straight-line method over a three-year estimated useful life for computer equipment, which is the only type of property and equipment the Company holds. Expenditures for repairs and maintenance of assets are charged to expense as incurred. Upon retirement or sale, the cost and related accumulated depreciation of assets disposed of are removed from the accounts and any resulting gain or loss is included in loss from operations.
	Impairment of Long-Lived Assets
	Long-lived assets consist of property and equipment. Long-lived assets to be held and used are tested for recoverability 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.
	Research and Development Costs
	Research and development costs are expensed as incurred. Included in research and development expenses are salaries, 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 manufacturing expenses and external costs of outside vendors engaged to conduct both preclinical studies and clinical trials. The Company expenses raw materials used to manufacture its drug substance when received.
	As part of the process of preparing consolidated financial statements, the Company is required to estimate its accrued research and development expenses. This process involves reviewing open contracts and purchase orders, communicating with company personnel and outside vendors to identify services that have been performed on the Company’s behalf and estimating the level of service performed and the associated costs incurred for the services when the Company has not yet been invoiced or otherwise notified of the actual costs. The majority of the Company’s service providers invoice in arrears for services performed, on a pre-determined schedule or when contractual milestones are met; however, some require advanced payments. The Company makes estimates of its accrued expenses as of each balance sheet date in its consolidated financial statements based on facts and circumstances known to the Company at that time. Examples of estimated accrued research and development expenses include fees paid to:
		•		clinical research organizations in connection with clinical trials;
		•		investigative sites or other providers in connection with clinical trials;
		•		vendors in connection with preclinical development activities; and
		•		vendors related to product manufacturing, development and distribution of clinical supplies.
	The Company bases its expenses related to clinical trials on its estimates of the services received and efforts expended pursuant to contracts with multiple clinical research organizations and investigative sites that manage and conduct clinical trials on the Company’s behalf. The financial terms of these agreements are subject to negotiation, vary from contract to contract and may result in uneven payment flows. There may be instances in which payments made to vendors will exceed the level of services provided and result in a prepayment of the clinical expense. Payments under some of these contracts depend on factors such as the successful enrollment of patients and the completion of clinical trial milestones. In accruing service fees, the Company estimates the time period over which services will be performed, enrollment of patients, number of sites activated and the level of effort to be expended in each period. If the actual timing of the performance of services or the level of effort varies from its estimate, the Company adjusts the accrual or amount of prepaid expense accordingly. Although the Company does not expect its estimates to be materially different from amounts actually incurred, its understanding of the status and timing of services performed relative to the actual status and timing of services performed may vary and may result in the Company reporting amounts that are too high or too low in any particular period. To date, the Company has not made any material adjustments to its prior estimates of accrued research and development expenses.
	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 and directors 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, while the graded vesting method is applied to all grants with both service and performance conditions.
	For stock-based awards granted to non-employees, compensation expense is recognized over the period during which services are rendered by such non-employees until completed. At the end of each financial reporting period prior to completion of the service, the fair value of the unvested portion of the awards is re-measured using the then-current fair value of the Company’s common stock and updated assumption inputs in the Black-Scholes option-pricing model.
	The Company classifies stock-based compensation expense in its consolidated statement of operations and comprehensive loss in the same manner in which the award recipient’s payroll costs are classified or in which the award recipient’s service payments are classified.
	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.
	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 consolidated financial statements or in the Company’s tax returns. Deferred taxes are determined based on the difference between the financial statement 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 consolidated 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 consolidated 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.
	Segment Data
	The Company manages its operations as a single segment for the purposes of assessing performance and making operating decisions. The Company’s singular focus is on developing novel proprietary therapies for the treatment of prostate cancer and other hormonally-driven diseases. No revenue has been generated since inception, and all tangible assets are held in the United States.
	Comprehensive Loss
	Comprehensive loss includes net loss as well as other changes in stockholders’ equity (deficit) that result from transactions and economic events other than those with stockholders. For the years ended December 31, 2014, 2013 and 2012, there was no difference between net loss and comprehensive loss.
	Net Income (Loss) Per Share
	In September 2014, upon the closing of the IPO, all of the outstanding shares of the Company’s redeemable convertible preferred stock automatically converted into 14,860,173 shares of the Company’s common stock. Prior to this conversion, the Company followed the two-class method when computing net income (loss) per share as the Company had issued shares that met the definition of participating securities. The two-class method determines 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 requires 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 stock 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, the two-class method did not apply for periods in which the Company reported a net loss or a net loss attributable to common stockholders resulting from dividends or accretion related to its redeemable convertible preferred stock.
	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 common shares outstanding for the period. 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, including potential dilutive common shares assuming the dilutive effect of outstanding stock options and unvested restricted common shares, as determined using the treasury stock method. For periods in which the Company has reported net losses, diluted net loss per common share attributable to common stockholders is the same as basic net loss per common share attributable to common stockholders, since dilutive common shares are not assumed to have been issued if their effect is anti-dilutive.
	The following common stock equivalents outstanding as of December 31, 2014, 2013 and 2012 were excluded from the computation of diluted net loss per share for the years ended December 31, 2014, 2013 and 2012, because they had an anti-dilutive impact:
			December 31,
			2014		2013		2012
	Stock options to purchase common stock			2,146,927		1,124,116		807,657
	Restricted common stock units			54,604		—		139,557
	Redeemable convertible preferred stock (as converted to common stock)			—		14,860,173		9,426,337
	Total options, restricted stock units and redeemable convertible preferred stock exercisable or convertible into common stock			2,201,531		15,984,289		10,373,551
	Recently Issued and Adopted Accounting Pronouncements
	In June 2014, the FASB issued Accounting Standards Update 2014-10, Development Stage Entities (Topic 915): Elimination of Certain Financial Reporting Requirements, Including an Amendment to Variable Interest Entities Guidance in Topic 810, Consolidation. The amendments in this guidance remove all incremental financial reporting requirements for development stage entities. Among other changes, this guidance will no longer require development stage entities to present inception-to-date information about income statement line items, cash flows, and equity transactions. This guidance is effective for public companies in the first annual period beginning after December 15, 2014 with early adoption permitted. The Company elected to apply this disclosure guidance to its financial statements for the year ended December 31, 2014 and as a result, no longer discloses inception-to-date information in its statements of operations and comprehensive loss, changes in redeemable convertible preferred stock and stockholders’ equity (deficit) and cash flows and the related notes thereto.
	In August 2014, the FASB issued ASU 2014-15, Presentation of Financial Statements — Going Concern (Subtopic 205-40). The new guidance addresses management’s responsibility to evaluate whether there is substantial doubt about an entity’s ability to continue as a going concern and to provide related footnote disclosures. Management’s evaluation should be based on relevant conditions and events that are known and reasonably knowable at the date that the financial statements are issued. The standard will be effective for the first interim period within annual reporting periods beginning after December 15, 2016. Early adoption is permitted. The Company is evaluating the effect that this guidance will have on its consolidated financial statements.

Property_and_Equipment_net

Property and Equipment, net	12 Months Ended
	Dec. 31, 2014
Property, Plant and Equipment [Abstract]
Property and Equipment, net	3. Property and Equipment, net
		December 31,
		2014			2013
	Computer equipment	$	91		$	72
			91			72
	Less: Accumulated depreciation		(58	)		(43	)
		$	33		$	29
	Depreciation expense was $21, $10 and $9 for the years ended December 31, 2014, 2013 and 2012, respectively.

Accrued_Expenses

Accrued Expenses	12 Months Ended
	Dec. 31, 2014
Payables and Accruals [Abstract]
Accrued Expenses	4. Accrued Expenses
	Accrued expenses consisted of the following as of December 31, 2014 and 2013:
		December 31,
		2014		2013
	Accrued research and development expenses	$	1,853	$	1,370
	Accrued payroll and related expenses		963		436
	Accrued professional fees		497		338
	Accrued other		165		60
		$	3,478	$	2,204

Redeemable_Convertible_Preferr

Redeemable Convertible Preferred Stock	12 Months Ended
	Dec. 31, 2014
Equity [Abstract]
Redeemable Convertible Preferred Stock	5. Redeemable Convertible Preferred Stock
	During 2012, the Company issued 34,696,042 shares of Series D-3 redeemable convertible preferred stock to certain existing investors at $0.54617142 per share for gross proceeds of $18,950. The Company incurred issuance costs of $34 in connection with the sale and issuance of these shares of Series D-3 redeemable convertible preferred stock.
	In May and October 2013, the Company issued an aggregate of 56,892,391 shares of Series E redeemable convertible preferred stock to existing and new investors at $0.62398475 per share for gross proceeds of $35,500.
	The Company incurred issuance costs of $94 in connection with the sale and issuance of these shares of Series E redeemable convertible preferred stock.
	Redeemable Preferred Stock consisted of the following as of December 31, 2013:
		Preferred		Preferred		Liquidation		Carrying		Common
		Shares		Shares		Preference		Value		Stock
		Authorized		Issued and						Issuable
				Outstanding						Upon
										Conversion
	Series A redeemable convertible preferred stock		4,500,000		4,500,000	$	2,961	$	2,961		429,799
	Series B-1 redeemable convertible preferred stock		798,067		798,067		525		525		76,224
	Series B-2 redeemable convertible preferred stock		1,503,819		1,503,819		989		989		143,631
	Series C redeemable convertible preferred stock		15,999,998		15,999,998		3,330		3,920		1,528,176
	Series D-1 redeemable convertible preferred stock		29,294,828		29,294,828		14,773		16,000		2,797,978
	Series D-2 redeemable convertible preferred stock		3,661,846		3,661,846		2,000		2,000		349,747
	Series D-3 redeemable convertible preferred stock		42,935,192		42,935,192		23,450		23,450		4,100,782
	Series E redeemable convertible preferred stock		56,892,391		56,892,391		35,500		35,500		5,433,836
			155,586,141		155,586,141	$	83,528	$	85,345		14,860,173
	Upon the closing of the Company’s IPO in September 2014 (Note 6), all outstanding shares of the Company’s redeemable convertible preferred stock were converted into 14,860,173 shares of common stock.
	Prior to the conversion, the rights and preferences of the Company’s outstanding redeemable convertible preferred stock were as follows:
	Voting Rights
	The holders of Redeemable Preferred Stock are entitled to vote, together with the holders of common stock, on all matters submitted to stockholders for a vote. Holders of all Redeemable Preferred Stock, with the exception of holders of Series C redeemable convertible preferred stock, had the right to vote the number of shares equal to the number of shares of common stock into which such Redeemable Preferred Stock could convert on the record date for determination of stockholders entitled to vote. Holders of Series C redeemable convertible preferred stock were entitled to cast 0.45773175 of a vote for each share of common stock into which one share of Series C redeemable convertible preferred stock was convertible.
	Dividends
	The holders of all Redeemable Preferred Stock were entitled to receive dividends as specified in the Company’s certificate of incorporation, as amended and restated. Dividends were non-cumulative, and holders of Redeemable Preferred Stock holders were not entitled to any accruing dividends.
	Liquidation Preference
	In the event of any voluntary or involuntary liquidation, dissolution or winding up of the Company (each, a “Liquidation Event”), the redeemable convertible preferred stockholders were entitled to be paid out of the assets of the Company in the order and preference as specified in the Company’s certificate of incorporation, as amended and restated.
	Conversion
	Each share of Redeemable Preferred Stock was convertible at the option of the stockholder at any time without the payment of additional consideration, and automatically converted into shares of common stock upon the closing of the Company’s IPO in September 2014 on a 10.47-for-1 basis.
	Redemption Rights
	At any time on or after May 10, 2018, shares of each of the Series A, Series B-1 and Series B-2 redeemable convertible preferred stock were subject to mandatory redemption by the Company in three equal annual installments beginning 60 days after receipt of a notice of redemption from the holders of at least 60% of the combined voting power of the holders of the outstanding Series A, Series B-1 and Series B-2 redeemable convertible preferred stock, voting as a single class. As of December 31, 2013 the redemption price for the Series A, Series B-1 and Series B-2 redeemable convertible preferred stock was equal to $0.6581 per share, subject to appropriate adjustment for any stock splits, stock dividends, combinations or any other similar recapitalization affecting such shares, plus any dividends declared but unpaid thereon.
	At any time on or after May 10, 2018, shares of the Series C, Series D-1, Series D-2, Series D-3 and Series E convertible preferred stock were subject to mandatory redemption by the Company in three equal annual installments beginning 60 days after receipt of a notice of redemption from the holders of at least 75% of the combined voting power of holders of the outstanding Senior Preferred Stock. As of December 31, 2013, the redemption price for the Series C, Series D-1, Series D-2, Series D-3 and Series E convertible preferred stock was equal to $0.2081, $0.5043, $0.54617142, $0.54617142 and $0.62398475 per share, respectively, subject to appropriate adjustment for any stock splits, stock dividends, combinations or any other similar recapitalization affecting such shares, plus any dividends declared but unpaid thereon.

Common_Stock

Common Stock	12 Months Ended
	Dec. 31, 2014
Equity [Abstract]
Common Stock	6. Common Stock
	On August 29, 2014, the Company effected a 1-for-10.47 reverse stock split of its issued and outstanding shares of common stock. Accordingly, all share and per share amounts for all periods presented in these consolidated financial statements and notes thereto have been adjusted retroactively, where applicable, to reflect this reverse stock split.
	On September 22, 2014, the Company completed an IPO of its common stock and issued and sold 6,480,000 shares of common stock at a public offering price of $15.00 per share, resulting in net proceeds of $87,062 after deducting underwriting discounts and commissions and offering expenses. Upon the closing of the IPO, all outstanding shares of the Company’s redeemable convertible preferred stock automatically converted into 14,860,173 shares of the Company’s common stock. On October 9, 2014, the Company issued and sold an additional 540,000 shares of its common stock at the IPO price of $15.00 per share, pursuant to the underwriters’ partial exercise of their option to purchase additional shares of common stock, resulting in additional net proceeds to the Company of $7,533 after deducting underwriting discounts and commissions.
	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 not entitled to receive dividends, unless declared by the board of directors.

Diotima

Diotima	12 Months Ended
	Dec. 31, 2014
Equity Method Investments and Joint Ventures [Abstract]
Diotima	7. Diotima
	The Company had a variable interest entity, Diotima, in which the Company had a variable financial interest and was the primary beneficiary but had no ownership interest. Accordingly, the Company consolidated Diotima. Expenses incurred by Diotima for the years ended December 31, 2014, 2013 and 2012 were $8, $60 and $85, respectively. In 2014, the Diotima’s license agreements were terminated. In April 2014, the board of directors and stockholders of Diotima approved the dissolution of Diotima, and Diotima was dissolved.

StockBased_Awards

Stock-Based Awards	12 Months Ended
	Dec. 31, 2014
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Stock-Based Awards	8. Stock-Based Awards
	2007 Stock Incentive Plan
	Under the Company’s 2007 Stock Incentive Plan, as amended (the “2007 Plan”), the Company was authorized to grant options, restricted stock, restricted stock units and other stock-based awards to the Company’s employees, officers, directors, consultants and advisors. As of December 31, 2013, a total of 1,590,580 shares of common stock were reserved for issuance under the 2007 Plan. The Company’s 2014 Stock Incentive Plan (the “2014 Plan”) became effective upon effectiveness of the registration statement for the IPO in September 2014. Upon the effectiveness of the 2014 Plan, 43,923 shares of common stock that remained available for grant under the 2007 Plan became available for grant under the 2014 Plan, and no further awards were available to be issued under the 2007 Plan.
	2014 Stock Incentive Plan
	In August 2014, the Company’s board of directors and stockholders approved the 2014 Plan, which became effective on September 16, 2014. Under the 2014 Plan, the Company may grant incentive stock options, non-statutory stock options, restricted stock, restricted stock units, stock appreciation rights and other stock-based awards to the Company’s employees, officers, directors, consultants and advisors; however, incentive stock options may only be granted to the Company’s employees. The number of shares reserved for issuance under the 2014 Plan is equal to the sum of (1) 1,700,000 shares of common stock, plus (2) the number of shares (up to 1,678,220 shares) equal to the sum of (i) 43,923 shares of common stock, which is the number of shares reserved for issuance under the 2007 Plan that remained available for grant under the 2007 Plan immediately prior to the effectiveness of the 2014 Plan, and (ii) the number of shares of common stock subject to outstanding awards under the 2007 Plan that expire, terminate or are otherwise surrendered, cancelled, forfeited or repurchased by the Company at their original issuance price pursuant to a contractual repurchase right, plus (3) an annual increase, to be added on the first day of each fiscal year, beginning with the fiscal year ending December 31, 2015 and continuing for each fiscal year until, and including, the fiscal year ending December 31, 2024, equal to the least of 1,800,000 shares of the Company’s common stock, 4% of the number of shares of the Company’s common stock outstanding on the first day of the applicable fiscal year and an amount determined by the Company’s board of directors. As of December 31, 2014, 1,176,086 shares remained available for issuance under the 2014 Plan. The number of authorized shares reserved for issuance under the 2014 Plan was increased by 895,305 shares effective as of January 1, 2015.
	As required by the 2007 Plan and 2014 Plan, the exercise price for stock options granted is not to be less than the fair value of common stock as of the date of grant. The Company bases fair value of common stock on the quoted market price. Prior to the IPO, the value of common stock was determined by the Company’s board of directors by taking into consideration its most recently available valuation of common stock performed by management and the board of directors as well as additional factors which might have changed since the date of the most recent contemporaneous valuation through the date of grant.
	During the years ended December 31, 2014, 2013 and 2012, the Company granted 1,039,155, 786,537 and 99,130 stock options, respectively, to certain employees, consultants and directors. The vesting of most of these awards is time-based and the restrictions typically lapse over three to four years.
	2014 Employee Stock Purchase Plan
	In August 2014, the Company’s board of directors and stockholders approved the 2014 Employee Stock Purchase Plan (the “ESPP”), which became effective on September 16, 2014. An aggregate of 225,000 shares of the Company’s common stock are reserved for issuance under the ESPP. The number of shares of the Company’s common stock reserved for issuance under the ESPP will automatically increase on the first day of each fiscal year, commencing on January 1, 2015 and ending on December 31, 2024, in an amount equal to the least of (1) 450,000 shares of the Company’s common stock, (2) 1% of the total number of shares of the Company’s common stock outstanding on the first day of the applicable fiscal year and (3) an amount determined by the Company’s board of directors. No offering periods have commenced under the ESPP and the number of shares reserved for issuance under the ESPP was not increased for the fiscal year beginning January 1, 2015.
	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 its IPO, the Company was a private company and lacked company-specific historical and implied volatility information. Therefore, the Company estimated its expected stock volatility based on the historical volatility of a publicly traded group of peer companies. The Company 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 expected term of stock options granted to non-employees is equal to the contractual term of the option award. 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 following table sets forth the assumptions that the Company used to determine the fair value of the stock options granted, presented on a weighted average basis:
		Year Ended December 31,
		2014			2013			2012
	Risk-free interest rate		1.83	%		1.72	%		0.79	%
	Expected term (in years)		5.95			5.98			6.07
	Expected volatility		79.4	%		79.7	%		65.5	%
	Expected dividend yield		0	%		0	%		0	%
	The following table summarizes the Company’s stock option activity from January 1, 2014 through December 31, 2014:
		Shares Issuable			Weighted			Weighted			Aggregate
		Under Options			Average			Average			Intrinsic
					Exercise			Remaining			Value
					Price			Contractual
								Term
								(In years)
	Outstanding as of December 31, 2013		1,124,116		$	1.59			8.8		$	2,346
	Granted		1,039,155			9.77
	Exercised		(8,875	)		1.64
	Forfeited		(7,469	)		2.21
	Outstanding as of December 31, 2014		2,146,927		$	5.54			8.6		$	19,802
	Options vested and expected to vest as of December 31, 2014		2,117,081		$	5.48			8.6		$	19,653
	Options exercisable as of December 31, 2014		922,838		$	2.08			7.8		$	11,682
	The aggregate intrinsic value was calculated based on the positive differences between the market value of the Company’s common stock on December 31, 2014 and 2013, of $14.74 and $3.67 per share, respectively, and the exercise prices of the options.
	The weighted average grant date fair value of stock options granted was $6.70, $1.17 and $0.84 per share for the years ended December 31, 2014, 2013 and 2012, respectively.
	The total intrinsic value of stock options exercised was $35, $33 and $1 for the years ended December 31, 2014, 2013 and 2012, respectively.
	Restricted Common Stock Units
	The 2014 Plan provides for the award of restricted common stock units. The Company has granted restricted common stock units with time-based vesting conditions. Unvested shares of restricted common stock may not be sold or transferred by the holder. These restrictions lapse according to the time-based vesting conditions of each award.
	The table below summarizes the Company’s restricted stock activity:
					Weighted
					Average Grant
		Shares			Date Fair Value
	Unvested restricted common stock as of December 31, 2013		—		$	—
	Issued		54,604			15
	Vested		—			—
	Forfeited		—			—
	Unvested restricted common stock as of December 31, 2014		54,604		$	15
	During 2014, the Company granted 54,604 restricted stock units with time-based vesting conditions which lapse over 4 years. Upon vesting, the restricted stock units entitle the holder to one share of common stock for each restricted stock unit. All restricted stock units currently granted have been classified as equity instruments as their terms require settlement in shares. Restricted stock units with time-based vesting conditions are valued on the grant date using the grant date market price of the underlying shares. As of December 31, 2014, the Company estimates that all shares of restricted stock units with an intrinsic value of $478 and a weighted average remaining contractual term of 3.67 years will ultimately vest. The Company did not grant restricted stock units in 2013 or 2012.
	Stock-based Compensation
	The Company recorded stock-based compensation expense related to stock options and restricted common stock in the following expense categories of its statements of operations:
		Year Ended December 31,
		2014			2013			2012
	Research and development	$	552		$	91		$	87
	General and administrative		1,556			147			123
		$	2,108		$	238		$	210
	Stock-based compensation expense for the year ended December 31, 2014 includes $880 of stock-based compensation expense related to a performance-based option grant which vested during 2014. As of December 31, 2014, the Company had an aggregate of $7,044 of unrecognized stock-based compensation cost, which is expected to be recognized over a weighted average period of 3.41 years.

Commitments_and_Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2014
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	9. Commitments and Contingencies
	Leases
	The Company leases its office space and obtains certain office-related services on a month-to-month basis under a 30-day cancelable operating service agreement. Payments under this service agreement include monthly rent and certain fee-for-service charges.
	During the years ended December 31, 2014, 2013 and 2012, the Company recognized $520, $366 and $341, respectively, of rental expense related to office space.
	In February 2015, the Company entered into a sublease with a Massachusetts limited liability company (the “sublandlord”) for 15,981 square feet of office space in Boston, Massachusetts. The sublease is subject and subordinate to a prime lease, dated October 5, 2010, with the prime landlord. The term of the sublease commences on April 1, 2015 and expires on December 31, 2016. However, if the term of the prime lease is terminated for any reason prior to the expiration or earlier termination of the sublease, the sublease will immediately terminate and the Company will have no recourse against the sublandlord for such termination. Future minimum lease payments under this lease will be $408 and $555 for the years ending December 31, 2015 and 2016, respectively, aggregating $963 in total minimum lease payments. The Company will record exit costs of $133 in the first quarter of 2015 in connection with terminating its existing lease.
	Intellectual Property Licenses
	The Company has a master license agreement with the University of Maryland, Baltimore (“UMB”). Pursuant to the license agreement, UMB granted an exclusive worldwide license, with the right to sublicense, under certain patents and patent applications to make, have made, use, sell, offer to sell and import certain anti-androgen steroids including galeterone for the prevention, diagnosis, treatment or control of any human or animal disease. In addition, UMB granted the Company a first option to receive an exclusive license to UMB’s rights in certain improvements to the licensed products. The Company has exercised the option and acquired exclusive rights to licensed improvements under three amendments to the license agreement.
	The Company is obligated to pay UMB an annual maintenance fee of $10 each year until the first commercial sale of a product developed using the licensed technology. The Company is also obligated to make an additional $50 milestone payment to UMB for each additional IND filed for a licensed product and a $100 milestone payment upon the approval of each NDA for a licensed product by the U.S. Food and Drug Administration. Because the achievement of these milestones has not occurred as of December 31, 2014, no liabilities for such milestone payments have been recorded in the Company’s consolidated financial statements.
	The Company must also pay UMB low-single digit percentage royalties on aggregate worldwide net sales of licensed products, including sales by sublicensees, on a licensed product-by-licensed product and country-by-country basis until the later of the expiration of the last-to-expire applicable licensed patent or ten years after first commercial sale of the applicable licensed product, in each case in the applicable country. The royalty obligations are subject to specified reductions in the event that additional licenses need to be obtained from third parties or in the event of specified competition from third-party products licensed by UMB. Minimum annual royalty payments to UMB are $50 beginning in the year following the year in which the first commercial sale occurs. The Company must also pay UMB 10% of all non-royalty sublicense income received from sublicensees. Finally, the Company is responsible for all patent expenses related to the prosecution and maintenance of the licensed patents. As of December 31, 2014, the Company has not yet developed a commercial product using the licensed technologies, and it has not entered into any sublicense agreements for the technologies. In connection with this license agreement, the Company incurred license, milestone and maintenance fees of $10, $20 and $60 for the years ended December 31, 2014, 2013 and 2012, respectively.
	In January 2015, the Company entered into an exclusive license agreement with The Johns Hopkins University (“Johns Hopkins”). Pursuant to the license agreement, Johns Hopkins granted the Company an exclusive worldwide license under certain patent applications and a non-exclusive license under certain know-how, with the right to sublicense, to make, have made, use, sell, offer to sell and import certain assays to identify androgen receptor variants for use as a companion diagnostic with galeterone. In addition, Johns Hopkins granted the Company an option to negotiate an exclusive license to Johns Hopkins’s rights in certain improvements to the licensed products.
	Under the terms of the license agreement, the Company is obligated to diligently develop, manufacture and sell licensed products. The Company is also obligated to use commercially reasonable efforts to achieve specified milestone events by specified dates. Unless the license agreement with Johns Hopkins is terminated earlier as provided below, the license from Johns Hopkins expires on a country-by-country basis as of the later of the expiration date of the last to expire of the claims of the patent rights licensed under the agreement in such country or ten years after the first commercial sale of a licensed product in such country. Johns Hopkins may terminate the agreement if the Company fails to achieve such milestone events and does not cure such failure within a specified termination notice period. Johns Hopkins may also terminate the agreement upon a material breach by the Company under the agreement if the Company does not cure such breach within a specified notice period or upon the Company’s bankruptcy or insolvency. The Company may terminate the agreement at any time upon 90 days’ notice.
	In consideration for the rights granted to the Company under the license agreement, the Company made an upfront payment to Johns Hopkins of $75 following the execution of the license agreement. The Company is obligated to pay Johns Hopkins an annual minimum royalty of up to $30. The Company is also obligated to make milestone payments to Johns Hopkins upon the achievement of specified technical and commercial milestones. If all such milestones were achieved, the total milestone payments owed to Johns Hopkins would equal in the aggregate $700. The Company must also pay Johns Hopkins single digit percentage royalties on aggregate worldwide net sales of licensed products (and not galeterone), including sales by sublicensees, on a licensed product-by-licensed product and country-by-country basis until the later of the expiration of the last-to-expire applicable licensed patent or ten years after first commercial sale of the applicable licensed product, in each case in the applicable country. These royalty obligations are subject to specified reductions in the event that additional licenses from third parties are required. The Company must also pay Johns Hopkins 20% of all non-royalty sublicense income received from sublicensees and reimburse Johns Hopkins for patent costs.
	Commercial Development Agreement
	In March 2015, the Company entered into a project work plan with Qiagen Manchester Limited (“Qiagen”) under a Master Collaboration Agreement, dated January 12, 2015, between the Company and Qiagen (together with the project work plan, the “Agreement”). Pursuant to the Agreement, Qiagen has agreed to develop and commercialize an assay as a companion diagnostic test to identify castration resistant prostate cancer (“CRPC”) patients with the splice variant AR-V7 for use with galeterone, the Company’s lead drug candidate. The Company expects to use the clinical trial assay developed by Qiagen in its planned pivotal Phase 3 clinical trial of galeterone in order to identify CRPC patients with AR-V7.
	Under the Agreement, Qiagen is responsible for developing, and obtaining and maintaining regulatory approvals for, the companion diagnostic test in the United States, the European Union, Canada, Australia and such other countries as the parties may agree. In addition, Qiagen has agreed to use commercially reasonable and diligent efforts to manufacture the companion diagnostic test and to make the companion diagnostic test commercially available in those countries in which the Company has obtained regulatory approval for, and has valid patent claims covering, galeterone. Qiagen will be responsible for commercializing the companion diagnostic in each such country. If Qiagen elects not to commercialize the companion diagnostic test itself in any such country, for so long as there are valid patent claims covering galeterone in such country, Qiagen has agreed to procure alternative distribution channels or otherwise supply the companion diagnostic test to the Company in order for the Company to market galeterone in combination with the companion diagnostic test. Upon the request of the Company, the parties have also agreed to negotiate in good faith to expand the scope of the projects under the Agreement to, among other things, provide for the development and commercialization of the companion diagnostic test for use with galeterone in Japan.
	Subject to the terms of the Agreement, the Company will pay Qiagen a fee for the exclusive right to have the circulating tumor cell enrichment technology used in the development of the companion diagnostic test, fees for the development of the assay and a contingent milestone payment of $1,000 upon Qiagen obtaining pre-market approval of the assay, and will reimburse Qiagen for certain direct out-of-pocket costs incurred by Qiagen, including for sample material. These amounts are subject to adjustment if the parties determine that changes in the scope of the development program are required. Following commercialization, the Company will have no further payment obligations to Qiagen under the Agreement. However, the Company will not receive any revenues from future sales, if any, of the companion diagnostic test.
	The Agreement expires on the later to occur of (i) the fifth anniversary of regulatory approval of the companion diagnostic test and (ii) the expiration of Qiagen’s commercialization obligations under the Agreement. The Company is permitted to terminate the Agreement for convenience upon 180 days’ written notice to Qiagen. Either party may terminate the Agreement upon 60 days’ written notice to the other party based on uncured material breaches by the other party and may terminate the Agreement immediately based on the bankruptcy or insolvency of the other party.
	Advisor Agreement
	The Company paid a financial advisor $1,053 that was contingent upon the closing of its IPO in connection with strategic and financial advisory services unrelated to the offering. The Company recorded this amount as general and administrative expenses in its consolidated statement of operations and comprehensive loss for the year ended December 31, 2014.
	Indemnification Agreements
	In the ordinary course of business, the Company may provide indemnification of varying scope and terms to vendors, lessors, business partners, and other parties with respect to certain matters including, but not limited to, losses arising out of breach of such agreements or from intellectual property infringement claims made by third parties. 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 directors and officers 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 consolidated financial statements as of December 31, 2014.

Income_Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2014
Income Tax Disclosure [Abstract]
Income Taxes	10. Income Taxes
	During the years ended December 31, 2014, 2014 and 2013, the Company recorded no income tax benefits for the net operating losses incurred in each year, due to its uncertainty of realizing a benefit from those items.
	A reconciliation of the U.S. federal statutory income tax rate to the Company’s effective income tax rate is as follows:
		Year Ended December 31,
		2014			2013			2012
	Federal statutory income tax rate		(34.0	%)		(34.0	%)		(34.0	%)
	Federal research and development tax credit		(0.9	)		(0.7	)		(1.2	)
	State taxes, net of federal benefit		(4.5	)		(5.6	)		(5.4	)
	Stock-based compensation expense		1.1			0.4			0.6
	Other		0.2			0.1			—
	Change in deferred tax asset valuation allowance		38.1			39.8			40
	Effective income tax rate		0	%		0	%		0	%
	Net deferred tax assets as of December 31, 2014 and 2013 consisted of the following:
		December 31,
		2014			2013
	Current deferred tax assets:
	Accrued expenses	$	414		$	201
	Total current deferred tax assets		414			201
	Noncurrent deferred tax assets:
	Capitalized research and development expenses		24,945			19,250
	Net operating loss carryforwards		6,292			3,989
	Research and development tax credit carryforwards		1,008			889
	Other		613			73
	Total noncurrent deferred tax assets		32,858			24,201
	Total gross deferred tax assets		33,272			24,402
	Valuation allowance		(33,272	)		(24,402	)
	Net deferred tax assets	$	—		$	—
	Changes in the valuation allowance for deferred tax assets during the years ended December 31, 2014, 2013 and 2012 related primarily to the increase in net operating loss carryforwards, capitalized research and development expenses and research and development tax credit carryforwards and were as follows:
		Year Ended December 31,
		2014			2013			2012
	Valuation allowance as of beginning of year	$	24,402		$	18,138		$	14,129
	Decreases recorded as benefit to income tax provision		—			—			—
	Increases recorded to income tax provision		8,870			6,264			4,009
	Valuation allowance as of end of year	$	33,272		$	24,402		$	18,138
	As of December 31, 2014, the Company had net operating loss carryforwards for federal and state income tax purposes of $16,500 and $13,000, respectively, which begin to expire in 2024 and 2030, respectively. As of December 31, 2014, the Company also had available research and development tax credit carryforwards for federal and state income tax purposes of $809 and $302, respectively, which begin to expire in 2025 and 2023, 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, as amended (the “Code”) due to ownership changes that have occurred previously or 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. The Company has not conducted a formal study to assess whether a change of control has occurred or whether there have been multiple changes of control since inception due to the significant complexity and cost associated with such a study. If the Company has experienced a change of control, as defined by Section 382 of the Code, at any time since inception, utilization of the net operating loss carryforwards or research and development tax credit carryforwards may be subject to an annual limitation under Section 382 of the Code, which is determined by first multiplying the value of the Company’s stock at the time of the ownership change by the applicable long-term tax-exempt rate, and then could be subject to additional adjustments, as required. Any limitation may result in expiration of a portion of the net operating loss carryforwards or research and development tax credit carryforwards before utilization. Further, until a study is completed and any limitation is known, no amounts are being presented as an uncertain tax position.
	As of December 31, 2014 and 2013, the Company’s gross deferred tax asset balance of $33,272 and $24,402, respectively, was comprised principally of capitalized research and development expenses, net operating loss carryforwards, and research and development tax credit carryforwards.
	The Company has evaluated the positive and negative evidence bearing upon its ability to realize the deferred tax assets. Management has considered the Company’s history of cumulative net losses incurred since inception and its lack of commercialization of any products since inception and has concluded that it is more likely than not that the Company will not realize the benefits of the deferred tax assets. Accordingly, a full valuation allowance has been established against the deferred tax assets as of December 31, 2014 and 2013. Management reevaluates the positive and negative evidence at each reporting period.
	The Company has not recorded any amounts for unrecognized tax benefits as of December 31, 2014 or 2013.
	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 2011 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’s policy is to record interest and penalties related to income taxes as part of its income tax provision.

401k_Plan

401(k) Plan	12 Months Ended
	Dec. 31, 2014
Postemployment Benefits [Abstract]
401(k) Plan	11. 401(k) Plan
	The Company has a 401(k) plan available for participating employees who meet certain eligibility requirements. Eligible employees may defer a portion of their salary as defined by the plan. Company contributions to the plan may be made at the discretion of the Board of Directors. To date, the Company has not made any contributions to the plan.

Related_Party_Transactions

Related Party Transactions	12 Months Ended
	Dec. 31, 2014
Related Party Transactions [Abstract]
Related Party Transactions	12. Related Party Transactions
	The Company has an outstanding loan to a former advisor of the Company of $250 that accrued interest at 2.92% per annum that was due in 2007. In 2007, unpaid principal and interest in the amount of $220 was deemed uncollectable by the Company, and as a result, was fully reserved for by the Company. As of December 31, 2013, no payments had been received by the Company, and the unpaid principal and interest balance remained fully reserved. In 2014 the Company started to receive repayment of this note. The Company is recording payments received as other income in 2014 as cash is received. As a result, the Company recorded other income of $158 for the year ended December 31, 2014 representing cash collected during that period.

Selected_Quarterly_Financial_D

Selected Quarterly Financial Data (Unaudited)	12 Months Ended
	Dec. 31, 2014
Quarterly Financial Information Disclosure [Abstract]
Selected Quarterly Financial Data (Unaudited)	13. Selected Quarterly Financial Data (Unaudited)
		Three Months Ended
		Dec. 31,			Sept. 30,			June 30,			March 31,			Dec. 31,			Sept. 30,			June 30,			March 31,
		2014			2014			2014			2014			2013			2013			2013			2013
	Statements of Operations Data:
	Revenue	$	—		$	—		$	—		$	—		$	—		$	—		$	—		$	—
	Loss from operations		(6,261	)		(6,424	)		(5,885	)		(4,892	)		(5,549	)		(3,365	)		(4,444	)		(2,391	)
	Net loss		(6,208	)		(6,390	)		(5,851	)		(4,847	)		(5,525	)		(3,365	)		(4,445	)		(2,390	)
	Net loss attributable to common stockholders		(6,208	)		(6,390	)		(5,851	)		(4,847	)		(5,540	)		(3,365	)		(4,524	)		(2,390	)
	Basic and diluted net loss attributable to common stockholders per share	$	(0.28	)	$	(2.71	)	$	(11.68	)	$	(9.79	)	$	(11.23	)	$	(6.82	)	$	(12.95	)	$	(7.20	)

Summary_of_Significant_Account1

Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2014
Accounting Policies [Abstract]
Use of Estimates	Use of Estimates
	The preparation of financial statements in conformity with GAAP requires management to make estimates, assumptions and judgments 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 expenses during the reporting periods. Significant estimates, assumptions and judgments reflected in these consolidated financial statements include, but are not limited to, the accrual of research and development expenses, the valuation of common stock and redeemable convertible preferred stock prior to the Company’s IPO and the valuation of stock-based awards. Estimates are periodically reviewed in light of changes in circumstances, facts and experience. Actual results could differ from the Company’s estimates.
Cash Equivalents	Cash Equivalents
	The Company considers all short-term, highly liquid investments with original maturities of ninety days or less at date of purchase to be cash equivalents. Cash equivalents, which consist of money market accounts, are stated at fair value.
Concentration of Credit Risk and of Significant Suppliers	Concentration of Credit Risk and of Significant Suppliers
	Financial instruments that potentially expose the Company to concentrations of credit risk consist primarily of cash and cash equivalents. The Company has all cash and cash equivalents 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 is dependent on third-party manufacturers to supply products for research and development activities in its programs. In particular, the Company relies and expects to continue to rely on a small number of manufacturers to supply it with its requirements for the active pharmaceutical ingredients and formulated drugs related to these programs. These programs could be adversely affected by a significant interruption in the supply of active pharmaceutical ingredients and formulated drugs.
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. Financial assets and liabilities carried at fair value are to be classified and disclosed in one of the following three levels of the fair value hierarchy, of which the first two are considered observable and the last is considered unobservable:
		•		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 of $91,316 and $1,311 as of December 31, 2014 and 2013, respectively, were carried at fair value based on Level 2 inputs. The carrying values of accounts payable and accrued expenses approximate their fair value due to the short-term nature of these liabilities.
Deferred Offering Costs	Deferred Offering Costs
	The Company capitalizes certain legal, accounting and other third-party fees that are directly associated with in-process equity financings as other assets until such financings are consummated. After consummation of the equity financing, these costs are recorded in stockholders’ equity (deficit) as a reduction of additional paid-in capital generated as a result of the offering or as a reduction to the carrying value of preferred stock issued. As of December 31, 2013, the Company had recorded $30 of deferred offering costs, included in other assets in the accompanying consolidated balance sheet in contemplation of the Company’s IPO, which closed in September 2014. The Company has no deferred offering costs as of December 31, 2014.
Property and Equipment	Property and Equipment
	Property and equipment are stated at cost less accumulated depreciation. Depreciation expense is recognized using the straight-line method over a three-year estimated useful life for computer equipment, which is the only type of property and equipment the Company holds. Expenditures for repairs and maintenance of assets are charged to expense as incurred. Upon retirement or sale, the cost and related accumulated depreciation of assets disposed of are removed from the accounts and any resulting gain or loss is included in loss from operations.
Impairment of Long-Lived Assets	Impairment of Long-Lived Assets
	Long-lived assets consist of property and equipment. Long-lived assets to be held and used are tested for recoverability 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.
Research and Development Costs	Research and Development Costs
	Research and development costs are expensed as incurred. Included in research and development expenses are salaries, 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 manufacturing expenses and external costs of outside vendors engaged to conduct both preclinical studies and clinical trials. The Company expenses raw materials used to manufacture its drug substance when received.
	As part of the process of preparing consolidated financial statements, the Company is required to estimate its accrued research and development expenses. This process involves reviewing open contracts and purchase orders, communicating with company personnel and outside vendors to identify services that have been performed on the Company’s behalf and estimating the level of service performed and the associated costs incurred for the services when the Company has not yet been invoiced or otherwise notified of the actual costs. The majority of the Company’s service providers invoice in arrears for services performed, on a pre-determined schedule or when contractual milestones are met; however, some require advanced payments. The Company makes estimates of its accrued expenses as of each balance sheet date in its consolidated financial statements based on facts and circumstances known to the Company at that time. Examples of estimated accrued research and development expenses include fees paid to:
		•		clinical research organizations in connection with clinical trials;
		•		investigative sites or other providers in connection with clinical trials;
		•		vendors in connection with preclinical development activities; and
		•		vendors related to product manufacturing, development and distribution of clinical supplies.
	The Company bases its expenses related to clinical trials on its estimates of the services received and efforts expended pursuant to contracts with multiple clinical research organizations and investigative sites that manage and conduct clinical trials on the Company’s behalf. The financial terms of these agreements are subject to negotiation, vary from contract to contract and may result in uneven payment flows. There may be instances in which payments made to vendors will exceed the level of services provided and result in a prepayment of the clinical expense. Payments under some of these contracts depend on factors such as the successful enrollment of patients and the completion of clinical trial milestones. In accruing service fees, the Company estimates the time period over which services will be performed, enrollment of patients, number of sites activated and the level of effort to be expended in each period. If the actual timing of the performance of services or the level of effort varies from its estimate, the Company adjusts the accrual or amount of prepaid expense accordingly. Although the Company does not expect its estimates to be materially different from amounts actually incurred, its understanding of the status and timing of services performed relative to the actual status and timing of services performed may vary and may result in the Company reporting amounts that are too high or too low in any particular period. To date, the Company has not made any material adjustments to its prior estimates of accrued research and development expenses.
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 and directors 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, while the graded vesting method is applied to all grants with both service and performance conditions.
	For stock-based awards granted to non-employees, compensation expense is recognized over the period during which services are rendered by such non-employees until completed. At the end of each financial reporting period prior to completion of the service, the fair value of the unvested portion of the awards is re-measured using the then-current fair value of the Company’s common stock and updated assumption inputs in the Black-Scholes option-pricing model.
	The Company classifies stock-based compensation expense in its consolidated statement of operations and comprehensive loss in the same manner in which the award recipient’s payroll costs are classified or in which the award recipient’s service payments are classified.
	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.
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 consolidated financial statements or in the Company’s tax returns. Deferred taxes are determined based on the difference between the financial statement 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 consolidated 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 consolidated 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.
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’s singular focus is on developing novel proprietary therapies for the treatment of prostate cancer and other hormonally-driven diseases. No revenue has been generated since inception, and all tangible assets are held in the United States.
Comprehensive Loss	Comprehensive Loss
	Comprehensive loss includes net loss as well as other changes in stockholders’ equity (deficit) that result from transactions and economic events other than those with stockholders. For the years ended December 31, 2014, 2013 and 2012, there was no difference between net loss and comprehensive loss.
Net Income (Loss) Per Share	Net Income (Loss) Per Share
	In September 2014, upon the closing of the IPO, all of the outstanding shares of the Company’s redeemable convertible preferred stock automatically converted into 14,860,173 shares of the Company’s common stock. Prior to this conversion, the Company followed the two-class method when computing net income (loss) per share as the Company had issued shares that met the definition of participating securities. The two-class method determines 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 requires 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 stock 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, the two-class method did not apply for periods in which the Company reported a net loss or a net loss attributable to common stockholders resulting from dividends or accretion related to its redeemable convertible preferred stock.
	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 common shares outstanding for the period. 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, including potential dilutive common shares assuming the dilutive effect of outstanding stock options and unvested restricted common shares, as determined using the treasury stock method. For periods in which the Company has reported net losses, diluted net loss per common share attributable to common stockholders is the same as basic net loss per common share attributable to common stockholders, since dilutive common shares are not assumed to have been issued if their effect is anti-dilutive.
	The following common stock equivalents outstanding as of December 31, 2014, 2013 and 2012 were excluded from the computation of diluted net loss per share for the years ended December 31, 2014, 2013 and 2012, because they had an anti-dilutive impact:
			December 31,
			2014		2013		2012
	Stock options to purchase common stock			2,146,927		1,124,116		807,657
	Restricted common stock units			54,604		—		139,557
	Redeemable convertible preferred stock (as converted to common stock)			—		14,860,173		9,426,337
	Total options, restricted stock units and redeemable convertible preferred stock exercisable or convertible into common stock			2,201,531		15,984,289		10,373,551
Recently Issued and Adopted Accounting Pronouncements	Recently Issued and Adopted Accounting Pronouncements
	In June 2014, the FASB issued Accounting Standards Update 2014-10, Development Stage Entities (Topic 915): Elimination of Certain Financial Reporting Requirements, Including an Amendment to Variable Interest Entities Guidance in Topic 810, Consolidation. The amendments in this guidance remove all incremental financial reporting requirements for development stage entities. Among other changes, this guidance will no longer require development stage entities to present inception-to-date information about income statement line items, cash flows, and equity transactions. This guidance is effective for public companies in the first annual period beginning after December 15, 2014 with early adoption permitted. The Company elected to apply this disclosure guidance to its financial statements for the year ended December 31, 2014 and as a result, no longer discloses inception-to-date information in its statements of operations and comprehensive loss, changes in redeemable convertible preferred stock and stockholders’ equity (deficit) and cash flows and the related notes thereto.
	In August 2014, the FASB issued ASU 2014-15, Presentation of Financial Statements — Going Concern (Subtopic 205-40). The new guidance addresses management’s responsibility to evaluate whether there is substantial doubt about an entity’s ability to continue as a going concern and to provide related footnote disclosures. Management’s evaluation should be based on relevant conditions and events that are known and reasonably knowable at the date that the financial statements are issued. The standard will be effective for the first interim period within annual reporting periods beginning after December 15, 2016. Early adoption is permitted. The Company is evaluating the effect that this guidance will have on its consolidated financial statements.

Summary_of_Significant_Account2

Summary of Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2014
Accounting Policies [Abstract]
Schedule of Common Stock Equivalents, Excluded from Computation of Diluted Net Loss per Share	The following common stock equivalents outstanding as of December 31, 2014, 2013 and 2012 were excluded from the computation of diluted net loss per share for the years ended December 31, 2014, 2013 and 2012, because they had an anti-dilutive impact:
		December 31,
		2014		2013		2012
	Stock options to purchase common stock		2,146,927		1,124,116		807,657
	Restricted common stock units		54,604		—		139,557
	Redeemable convertible preferred stock (as converted to common stock)		—		14,860,173		9,426,337
	Total options, restricted stock units and redeemable convertible preferred stock exercisable or convertible into common stock		2,201,531		15,984,289		10,373,551

Property_and_Equipment_net_Tab

Property and Equipment, net (Tables)	12 Months Ended
	Dec. 31, 2014
Property, Plant and Equipment [Abstract]
Schedule of Property and Equipment
		December 31,
		2014			2013
	Computer equipment	$	91		$	72
			91			72
	Less: Accumulated depreciation		(58	)		(43	)
		$	33		$	29

Accrued_Expenses_Tables

Accrued Expenses (Tables)	12 Months Ended
	Dec. 31, 2014
Payables and Accruals [Abstract]
Schedule of Accrued Expenses	Accrued expenses consisted of the following as of December 31, 2014 and 2013:
		December 31,
		2014		2013
	Accrued research and development expenses	$	1,853	$	1,370
	Accrued payroll and related expenses		963		436
	Accrued professional fees		497		338
	Accrued other		165		60
		$	3,478	$	2,204

Redeemable_Convertible_Preferr1

Redeemable Convertible Preferred Stock (Tables)	12 Months Ended
	Dec. 31, 2014
Equity [Abstract]
Redeemable Preferred Stock	Redeemable Preferred Stock consisted of the following as of December 31, 2013:
		Preferred		Preferred		Liquidation		Carrying		Common
		Shares		Shares		Preference		Value		Stock
		Authorized		Issued and						Issuable
				Outstanding						Upon
										Conversion
	Series A redeemable convertible preferred stock		4,500,000		4,500,000	$	2,961	$	2,961		429,799
	Series B-1 redeemable convertible preferred stock		798,067		798,067		525		525		76,224
	Series B-2 redeemable convertible preferred stock		1,503,819		1,503,819		989		989		143,631
	Series C redeemable convertible preferred stock		15,999,998		15,999,998		3,330		3,920		1,528,176
	Series D-1 redeemable convertible preferred stock		29,294,828		29,294,828		14,773		16,000		2,797,978
	Series D-2 redeemable convertible preferred stock		3,661,846		3,661,846		2,000		2,000		349,747
	Series D-3 redeemable convertible preferred stock		42,935,192		42,935,192		23,450		23,450		4,100,782
	Series E redeemable convertible preferred stock		56,892,391		56,892,391		35,500		35,500		5,433,836
			155,586,141		155,586,141	$	83,528	$	85,345		14,860,173

StockBased_Awards_Tables

Stock-Based Awards (Tables)	12 Months Ended
	Dec. 31, 2014
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Fair Value of Stock Options Granted	The following table sets forth the assumptions that the Company used to determine the fair value of the stock options granted, presented on a weighted average basis:
		Year Ended December 31,
		2014			2013			2012
	Risk-free interest rate		1.83	%		1.72	%		0.79	%
	Expected term (in years)		5.95			5.98			6.07
	Expected volatility		79.4	%		79.7	%		65.5	%
	Expected dividend yield		0	%		0	%		0	%
Summary of Stock Option Activity	The following table summarizes the Company’s stock option activity from January 1, 2014 through December 31, 2014:
		Shares Issuable			Weighted			Weighted			Aggregate
		Under Options			Average			Average			Intrinsic
					Exercise			Remaining			Value
					Price			Contractual
								Term
								(In years)
	Outstanding as of December 31, 2013		1,124,116		$	1.59			8.8		$	2,346
	Granted		1,039,155			9.77
	Exercised		(8,875	)		1.64
	Forfeited		(7,469	)		2.21
	Outstanding as of December 31, 2014		2,146,927		$	5.54			8.6		$	19,802
	Options vested and expected to vest as of December 31, 2014		2,117,081		$	5.48			8.6		$	19,653
	Options exercisable as of December 31, 2014		922,838		$	2.08			7.8		$	11,682
Summary of Restricted Stock Activity	The table below summarizes the Company’s restricted stock activity:
					Weighted
					Average Grant
		Shares			Date Fair Value
	Unvested restricted common stock as of December 31, 2013		—		$	—
	Issued		54,604			15
	Vested		—			—
	Forfeited		—			—
	Unvested restricted common stock as of December 31, 2014		54,604		$	15
Schedule of Stock-Based Compensation Expense Related to Stock Options and Restricted Common Stock	The Company recorded stock-based compensation expense related to stock options and restricted common stock in the following expense categories of its statements of operations:
		Year Ended December 31,
		2014			2013			2012
	Research and development	$	552		$	91		$	87
	General and administrative		1,556			147			123
		$	2,108		$	238		$	210

Income_Taxes_Tables

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2014
Income Tax Disclosure [Abstract]
Reconciliation of U.S. Federal Statutory Income 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 December 31,
		2014			2013			2012
	Federal statutory income tax rate		(34.0	%)		(34.0	%)		(34.0	%)
	Federal research and development tax credit		(0.9	)		(0.7	)		(1.2	)
	State taxes, net of federal benefit		(4.5	)		(5.6	)		(5.4	)
	Stock-based compensation expense		1.1			0.4			0.6
	Other		0.2			0.1			—
	Change in deferred tax asset valuation allowance		38.1			39.8			40
	Effective income tax rate		0	%		0	%		0	%
Schedule of Net Deferred Tax Assets	Net deferred tax assets as of December 31, 2014 and 2013 consisted of the following:
		December 31,
		2014			2013
	Current deferred tax assets:
	Accrued expenses	$	414		$	201
	Total current deferred tax assets		414			201
	Noncurrent deferred tax assets:
	Capitalized research and development expenses		24,945			19,250
	Net operating loss carryforwards		6,292			3,989
	Research and development tax credit carryforwards		1,008			889
	Other		613			73
	Total noncurrent deferred tax assets		32,858			24,201
	Total gross deferred tax assets		33,272			24,402
	Valuation allowance		(33,272	)		(24,402	)
	Net deferred tax assets	$	—		$	—
Summary of Changes in Valuation Allowance for Deferred Tax Assets	Changes in the valuation allowance for deferred tax assets during the years ended December 31, 2014, 2013 and 2012 related primarily to the increase in net operating loss carryforwards, capitalized research and development expenses and research and development tax credit carryforwards and were as follows:
		Year Ended December 31,
		2014			2013			2012
	Valuation allowance as of beginning of year	$	24,402		$	18,138		$	14,129
	Decreases recorded as benefit to income tax provision		—			—			—
	Increases recorded to income tax provision		8,870			6,264			4,009
	Valuation allowance as of end of year	$	33,272		$	24,402		$	18,138

Selected_Quarterly_Financial_D1

Selected Quarterly Financial Data (Unaudited) (Tables)	12 Months Ended
	Dec. 31, 2014
Quarterly Financial Information Disclosure [Abstract]
Schedule of Selected Quarterly Financial Data
		Three Months Ended
		Dec. 31,			Sept. 30,			June 30,			March 31,			Dec. 31,			Sept. 30,			June 30,			March 31,
		2014			2014			2014			2014			2013			2013			2013			2013
	Statements of Operations Data:
	Revenue	$	—		$	—		$	—		$	—		$	—		$	—		$	—		$	—
	Loss from operations		(6,261	)		(6,424	)		(5,885	)		(4,892	)		(5,549	)		(3,365	)		(4,444	)		(2,391	)
	Net loss		(6,208	)		(6,390	)		(5,851	)		(4,847	)		(5,525	)		(3,365	)		(4,445	)		(2,390	)
	Net loss attributable to common stockholders		(6,208	)		(6,390	)		(5,851	)		(4,847	)		(5,540	)		(3,365	)		(4,524	)		(2,390	)
	Basic and diluted net loss attributable to common stockholders per share	$	(0.28	)	$	(2.71	)	$	(11.68	)	$	(9.79	)	$	(11.23	)	$	(6.82	)	$	(12.95	)	$	(7.20	)

Nature_of_the_Business_and_Bas1

Nature of the Business and Basis of Presentation - Additional Information (Detail) (USD $)	0 Months Ended	1 Months Ended	12 Months Ended	0 Months Ended	12 Months Ended
In Thousands, except Share data, unless otherwise specified	Sep. 22, 2014	Sep. 30, 2014	Dec. 31, 2014	Oct. 09, 2014	Dec. 31, 2012	Dec. 31, 2013	Dec. 31, 2011
Ownership interest			0.00%
Proceeds from initial public offering, net of underwriting discounts and commissions			$97,929
Number of common shares issued on conversion of redeemable convertible preferred stock	14,860,173	14,860,173
Accumulated deficit			86,351			63,055
Cash and cash equivalents			105,256		11,691	31,753	2,253
Option to Purchase Additional Shares of Common Stock Granted to the Underwriters in Connection with the IPO [Member]
Common Stock, shares issued and sold				540,000
Common stock, public offering price per share				$15
Proceeds from initial public offering, net of underwriting discounts and commissions				7,533
Common Stock [Member]
Common Stock, shares issued and sold					154,973
Proceeds from initial public offering, net of underwriting discounts and commissions	87,062
Number of common shares issued on conversion of redeemable convertible preferred stock	14,860,173		14,860,173
Common Stock [Member] | IPO [Member]
Common Stock, shares issued and sold	6,480,000		7,020,000	540,000
Common stock, public offering price per share	15			$15
Proceeds from initial public offering, net of underwriting discounts and commissions				$7,533

Summary_of_Significant_Account3

Summary of Significant Accounting Policies - Additional Information (Detail) (USD $)	0 Months Ended	1 Months Ended	12 Months Ended
	Sep. 22, 2014	Sep. 30, 2014	Dec. 31, 2014	Dec. 31, 2013
Summary Of Significant Accounting Policies [Line Items]
Cash equivalents, maturity period			Ninety days or less
Deferred offering costs				$30,000
Property and equipment, estimated useful life			3 years
Impairment losses on long-lived assets			0
Income tax examination, likelihood of settlement, description			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.
Income tax examination, likelihood of settlement, percentage			50.00%
Number of common shares issued on conversion of redeemable convertible preferred stock	14,860,173	14,860,173
IPO [Member]
Summary Of Significant Accounting Policies [Line Items]
Deferred offering costs			0	30,000
Cash Equivalents [Member] | Fair Value, Inputs, Level 2 [Member]
Summary Of Significant Accounting Policies [Line Items]
Cash equivalents			$91,316,000	$1,311,000

Summary_of_Significant_Account4

Summary of Significant Accounting Policies - Schedule of Common Stock Equivalents, Excluded from Computation of Diluted Net Loss per Share (Detail)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total options, restricted stock units and redeemable convertible preferred stock exercisable or convertible into common stock	2,201,531	15,984,289	10,373,551
Stock Options to Purchase Common Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total options, restricted stock units and redeemable convertible preferred stock exercisable or convertible into common stock	2,146,927	1,124,116	807,657
Restricted Common Stock Units [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total options, restricted stock units and redeemable convertible preferred stock exercisable or convertible into common stock	54,604		139,557
Series A, B-1, B-2, C,D-1, D-2, D-3 and E Redeemable Convertible Preferred Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total options, restricted stock units and redeemable convertible preferred stock exercisable or convertible into common stock		14,860,173	9,426,337

Property_and_Equipment_net_Pro

Property and Equipment, net - Property and Equipment (Detail) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Property, Plant and Equipment [Line Items]
Property and Equipment, gross	$91	$72
Less: Accumulated depreciation	-58	-43
Property and Equipment, net	33	29
Computer Equipment [Member]
Property, Plant and Equipment [Line Items]
Property and Equipment, gross	$91	$72

Property_and_Equipment_net_Add

Property and Equipment, net - Additional Information (Detail) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Property, Plant and Equipment [Abstract]
Depreciation expense	$21	$10	$9

Accrued_Expenses_Schedule_of_A

Accrued Expenses - Schedule of Accrued Expenses (Detail) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified
Payables and Accruals [Abstract]
Accrued research and development expenses	$1,853	$1,370
Accrued payroll and related expenses	963	436
Accrued professional fees	497	338
Accrued other	165	60
Total	$3,478	$2,204

Redeemable_Convertible_Preferr2

Redeemable Convertible Preferred Stock - Additional Information (Detail) (USD $)	12 Months Ended
In Thousands, except Share data, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Sep. 30, 2014
Class of Stock [Line Items]
Preferred stock, shares issued	0	0
Preferred stock, proceeds from issuance		$35,406	$18,775
Preferred stock, issuance cost	3,304	30
Common stock, shares converted from redeemable convertible preferred stock		14,860,173		14,860,173
Conversion of Redeemable Preferred Stock	10.47-for-1 basis
Series D-3 Redeemable Convertible Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock, shares issued			34,696,042
Preferred stock, issuance price per share			$0.55
Preferred stock, proceeds from issuance			18,950
Preferred stock, issuance cost			34
Common stock, shares converted from redeemable convertible preferred stock		4,100,782
Installments of redemption of convertible preferred stock	3
Redemption price		$0.55
Redemption period after notice for redemption	60 days
Voting power, percentage	75.00%
Series E Redeemable Convertible Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock, shares issued		56,892,391
Preferred stock, issuance price per share		$0.62
Preferred stock, proceeds from issuance		35,500
Preferred stock, issuance cost		$94
Common stock, shares converted from redeemable convertible preferred stock		5,433,836
Installments of redemption of convertible preferred stock	3
Redemption price		$0.62
Redemption period after notice for redemption	60 days
Voting power, percentage	75.00%
Series C Redeemable Convertible Preferred Stock [Member]
Class of Stock [Line Items]
Common stock, shares converted from redeemable convertible preferred stock		1,528,176
Preferred stock, voting rights	$0.46
Installments of redemption of convertible preferred stock	3
Redemption price		$0.21
Redemption period after notice for redemption	60 days
Voting power, percentage	75.00%
Series A - Redeemable Convertible Preferred Stock [Member]
Class of Stock [Line Items]
Common stock, shares converted from redeemable convertible preferred stock		429,799
Installments of redemption of convertible preferred stock	3
Redemption price		$0.66
Redemption period after notice for redemption	60 days
Voting power, percentage	60.00%
Series B-1 Redeemable Convertible Preferred Stock [Member]
Class of Stock [Line Items]
Common stock, shares converted from redeemable convertible preferred stock		76,224
Installments of redemption of convertible preferred stock	3
Redemption price		$0.66
Redemption period after notice for redemption	60 days
Voting power, percentage	60.00%
Series B-2 Redeemable Convertible Preferred Stock [Member]
Class of Stock [Line Items]
Common stock, shares converted from redeemable convertible preferred stock		143,631
Installments of redemption of convertible preferred stock	3
Redemption price		$0.66
Redemption period after notice for redemption	60 days
Voting power, percentage	60.00%
Series D-1 Redeemable Convertible Preferred Stock [Member]
Class of Stock [Line Items]
Common stock, shares converted from redeemable convertible preferred stock		2,797,978
Installments of redemption of convertible preferred stock	3
Redemption price		$0.50
Redemption period after notice for redemption	60 days
Voting power, percentage	75.00%
Series D-2 Redeemable Convertible Preferred stock [Member]
Class of Stock [Line Items]
Common stock, shares converted from redeemable convertible preferred stock		349,747
Installments of redemption of convertible preferred stock	3
Redemption price		$0.55
Redemption period after notice for redemption	60 days
Voting power, percentage	75.00%

Redeemable_Convertible_Preferr3

Redeemable Convertible Preferred Stock - Redeemable Preferred Stock (Detail) (USD $)	Dec. 31, 2014	Sep. 30, 2014	Dec. 31, 2013
In Thousands, except Share data, unless otherwise specified
Schedule Of Redeemable Convertible Preferred Stock [Line Items]
Preferred Shares Authorized	0		155,586,141
Preferred Shares Issued	0		155,586,141
Preferred Shares Outstanding	0		155,586,141
Liquidation Preference			$83,528
Carrying Value			85,345
Common Stock Issuable Upon Conversion		14,860,173	14,860,173
Series A - Redeemable Convertible Preferred Stock [Member]
Schedule Of Redeemable Convertible Preferred Stock [Line Items]
Preferred Shares Authorized			4,500,000
Preferred Shares Issued			4,500,000
Preferred Shares Outstanding			4,500,000
Liquidation Preference			2,961
Carrying Value			2,961
Common Stock Issuable Upon Conversion			429,799
Series B-1 Redeemable Convertible Preferred Stock [Member]
Schedule Of Redeemable Convertible Preferred Stock [Line Items]
Preferred Shares Authorized			798,067
Preferred Shares Issued			798,067
Preferred Shares Outstanding			798,067
Liquidation Preference			525
Carrying Value			525
Common Stock Issuable Upon Conversion			76,224
Series B-2 Redeemable Convertible Preferred Stock [Member]
Schedule Of Redeemable Convertible Preferred Stock [Line Items]
Preferred Shares Authorized			1,503,819
Preferred Shares Issued			1,503,819
Preferred Shares Outstanding			1,503,819
Liquidation Preference			989
Carrying Value			989
Common Stock Issuable Upon Conversion			143,631
Series C Redeemable Convertible Preferred Stock [Member]
Schedule Of Redeemable Convertible Preferred Stock [Line Items]
Preferred Shares Authorized			15,999,998
Preferred Shares Issued			15,999,998
Preferred Shares Outstanding			15,999,998
Liquidation Preference			3,330
Carrying Value			3,920
Common Stock Issuable Upon Conversion			1,528,176
Series D-1 Redeemable Convertible Preferred Stock [Member]
Schedule Of Redeemable Convertible Preferred Stock [Line Items]
Preferred Shares Authorized			29,294,828
Preferred Shares Issued			29,294,828
Preferred Shares Outstanding			29,294,828
Liquidation Preference			14,773
Carrying Value			16,000
Common Stock Issuable Upon Conversion			2,797,978
Series D-2 Redeemable Convertible Preferred stock [Member]
Schedule Of Redeemable Convertible Preferred Stock [Line Items]
Preferred Shares Authorized			3,661,846
Preferred Shares Issued			3,661,846
Preferred Shares Outstanding			3,661,846
Liquidation Preference			2,000
Carrying Value			2,000
Common Stock Issuable Upon Conversion			349,747
Series D-3 Redeemable Convertible Preferred Stock [Member]
Schedule Of Redeemable Convertible Preferred Stock [Line Items]
Preferred Shares Authorized			42,935,192
Preferred Shares Issued			42,935,192
Preferred Shares Outstanding			42,935,192
Liquidation Preference			23,450
Carrying Value			23,450
Common Stock Issuable Upon Conversion			4,100,782
Series E Redeemable Convertible Preferred Stock [Member]
Schedule Of Redeemable Convertible Preferred Stock [Line Items]
Preferred Shares Authorized			56,892,391
Preferred Shares Issued			56,892,391
Preferred Shares Outstanding			56,892,391
Liquidation Preference			35,500
Carrying Value			$35,500
Common Stock Issuable Upon Conversion			5,433,836

Common_Stock_Additional_Inform

Common Stock - Additional Information (Detail) (USD $)	0 Months Ended	1 Months Ended	12 Months Ended		0 Months Ended
In Thousands, except Share data, unless otherwise specified	Sep. 22, 2014	Sep. 30, 2014	Dec. 31, 2014	Dec. 31, 2012	Oct. 09, 2014
Class of Stock [Line Items]
Reverse stock split conversion description			The Company effected a 1-for-10.47 reverse stock split of its issued and outstanding shares of common stock.
Proceeds from initial public offering, net of underwriting discounts and commissions			$97,929
Number of common shares issued on conversion of redeemable convertible preferred stock	14,860,173	14,860,173
Common Stock [Member]
Class of Stock [Line Items]
Shares issued				154,973
Proceeds from initial public offering, net of underwriting discounts and commissions	87,062
Number of common shares issued on conversion of redeemable convertible preferred stock	14,860,173		14,860,173
Common Stock [Member] | IPO [Member]
Class of Stock [Line Items]
Shares issued	6,480,000		7,020,000		540,000
Common stock, public offering price per share	15				$15
Proceeds from initial public offering, net of underwriting discounts and commissions					$7,533

Diotima_Additional_Information

Diotima - Additional Information (Detail) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Variable Interest Entity, Measure of Activity [Abstract]
Expense incurred by Diotima	$8	$60	$85

StockBased_Awards_Additional_I

Stock-Based Awards - Additional Information (Detail) (USD $)	12 Months Ended			0 Months Ended
In Thousands, except Share data, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Jan. 01, 2015	Sep. 30, 2014	Aug. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock options granted to employee	1,039,155	786,537	99,130
Market value of common stock	$14.74	$3.67
Weighted average grant date fair value of stock options granted	$6.70	$1.17	$0.84
Total intrinsic value of stock options exercised	$35	$33	$1
Restricted stock units with intrinsic value	19,802	2,346
Weighted average remaining contractual term	8 years 7 months 6 days	8 years 9 months 18 days
Unrecognized stock-based compensation cost	7,044
Weighted average period of unrecognized stock-based compensation cost expected to be recognized	3 years 4 months 28 days
Stock-based compensation expense	2,108	238	210
Restricted Common Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted stock units granted	54,604	0	0
Restricted stock units with intrinsic value	478
Weighted average remaining contractual term	3 years 8 months 1 day
Performance-based Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	$880
Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period of stock options	4 years
Maximum [Member] | Restricted Common Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period of stock options	4 years
Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period of stock options	3 years
2007 Stock Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock, shares authorized for issuance		1,590,580			43,923
2014 Stock Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock, shares authorized for issuance						1,700,000
Shares transferred from 2007 Stock Incentive Plan						43,923
Remaining shares available for issuance	1,176,086
2014 Stock Incentive Plan [Member] | Subsequent Event [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Maximum annual increase in common stock reserved for future issuance				1,800,000
Additional shares of common stock, percentage				4.00%
Increased number of shares reserved for issuance				895,305
2014 Stock Incentive Plan [Member] | Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares transferred from 2007 Stock Incentive Plan						1,678,220
2014 Employee Stock Purchase Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock, shares authorized for issuance						225,000
2014 Employee Stock Purchase Plan [Member] | Subsequent Event [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Maximum annual increase in common stock reserved for future issuance				450,000
Additional shares of common stock, percentage				1.00%
Increased number of shares reserved for issuance				0

StockBased_Awards_Fair_Value_o

Stock-Based Awards - Fair Value of Stock Options Granted (Detail)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Risk-free interest rate	1.83%	1.72%	0.79%
Expected term (in years)	5 years 11 months 12 days	5 years 11 months 23 days	6 years 26 days
Expected volatility	79.40%	79.70%	65.50%
Expected dividend yield	0.00%	0.00%	0.00%

StockBased_Awards_Summary_of_S

Stock-Based Awards - Summary of Stock Option Activity (Detail) (USD $)	12 Months Ended
In Thousands, except Share data, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Shares Issuable Under Options
Outstanding as of December 31, 2013	1,124,116
Granted	1,039,155	786,537	99,130
Exercised	-8,875
Forfeited	-7,469
Outstanding as of December 31, 2014	2,146,927	1,124,116
Options vested and expected to vest as of December 31, 2014	2,117,081
Options exercisable as of December 31, 2014	922,838
Weighted Average Exercise Price
Outstanding as of December 31, 2013	$1.59
Granted	$9.77
Exercised	$1.64
Forfeited	$2.21
Outstanding as of December 31, 2014	$5.54	$1.59
Options vested and expected to vest as of December 31, 2014	$5.48
Options exercisable as of December 31, 2014	$2.08
Weighted Average Remaining Contractual Term (In years)
Outstanding as of December 31, 2013	8 years 7 months 6 days	8 years 9 months 18 days
Options vested and expected to vest as of December 31, 2014	8 years 7 months 6 days
Options exercisable as of December 31, 2014	7 years 9 months 18 days
Aggregate Intrinsic Value
Outstanding as of December 31, 2013	$2,346
Outstanding as of December 31, 2014	19,802	2,346
Options vested and expected to vest as of December 31, 2014	19,653
Options exercisable as of December 31, 2014	$11,682

StockBased_Awards_Summary_of_R

Stock-Based Awards - Summary of Restricted Stock Activity (Detail) (Restricted Common Stock Units [Member], USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Restricted Common Stock Units [Member]
Shares
Issued	54,604	0	0
Vested	0
Forfeited	0
Unvested restricted common stock as of December 31, 2014	54,604
Weighted Average Grant Date Fair Value
Issued	$15
Vested	$0
Forfeited	$0
Unvested restricted common stock as of December 31, 2014	$15

StockBased_Awards_Schedule_of_

Stock-Based Awards - Schedule of Stock-Based Compensation Expense Related to Stock Options and Restricted Common Stock (Detail) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	$2,108	$238	$210
Research and Development [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	552	91	87
General and Administrative [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense	$1,556	$147	$123

Commitments_and_Contingencies_

Commitments and Contingencies (Leases) - Additional Information (Detail) (USD $)	12 Months Ended			3 Months Ended	1 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Mar. 31, 2015	Feb. 28, 2015
					sqft
Other Commitments [Line Items]
Operating service agreement period	30 days
Rental expense	$520	$366	$341
Subleases expiration date	31-Dec-16
Scenario Forecast [Member]
Other Commitments [Line Items]
Exit cost				133
Subsequent Event [Member] | Sublease [Member]
Other Commitments [Line Items]
Area of office space					15,981
Future minimum lease payments in 2015					408
Future minimum lease payments in 2016					555
Future minimum lease payments total					$963
License Agreement Terms [Member]
Other Commitments [Line Items]
Number of amendments	3

Commitments_and_Contingencies_1

Commitments and Contingencies (Intellectual Property Licenses) - Additional Information (Detail) (USD $)	12 Months Ended			1 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Jan. 31, 2015
Master License Agreement [Member] | UMB [Member]
Other Commitments [Line Items]
Annual maintenance fee	$10,000
Liabilities for milestone payments	0
Percentage of non-royalty sub license income	10.00%
License, milestone and maintenance fees	10,000	20,000	60,000
Master License Agreement [Member] | UMB [Member] | Minimum [Member]
Other Commitments [Line Items]
Annual royalty	50,000
License Agreement [Member] | Johns Hopkins [Member] | Subsequent Event [Member]
Other Commitments [Line Items]
Percentage of non-royalty sub license income				20.00%
Period to pay low percentage royalties after first commercial sale of licensed product				10 years
Agreement termination notice period				90 days
Upfront payment				75,000
Potential milestone payments under license agreement				700,000
License Agreement [Member] | Johns Hopkins [Member] | Minimum [Member] | Subsequent Event [Member]
Other Commitments [Line Items]
Annual royalty				30,000
IND [Member] | Master License Agreement [Member] | UMB [Member]
Other Commitments [Line Items]
Milestone payment	50,000
NDA [Member] | Master License Agreement [Member] | UMB [Member]
Other Commitments [Line Items]
Milestone payment	$100,000

Commitments_and_Contingencies_2

Commitments and Contingencies (Commercial Development Agreement) - Additional Information (Detail) (Master Collaboration Agreement [Member], Qiagen [Member], Subsequent Event [Member], USD $)	1 Months Ended
In Thousands, unless otherwise specified	Mar. 31, 2015
Master Collaboration Agreement [Member] | Qiagen [Member] | Subsequent Event [Member]
Other Commitments [Line Items]
Contingent Milestone Payment	$1,000
Agreement termination period by the company	180 days
Agreement termination period by both parties	60 days

Commitments_and_Contingencies_3

Commitments and Contingencies (Advisor Agreement) - Additional Information (Detail) (General and Administrative [Member], USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014
General and Administrative [Member]
Other Commitments [Line Items]
Fee paid to financial advisor	$1,053

Income_Taxes_Additional_Inform

Income Taxes - Additional Information (Detail) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
Tax Credit Carryforward [Line Items]
Income tax benefits	$0	$0
Net operating loss carryforwards for federal income tax purposes	16,500,000
Net operating loss carryforwards for State income tax purposes	13,000,000
Research and development tax credit carryforwards for federal and state income tax purposes	1,008,000	889,000
Deferred tax assets, Gross	33,272,000	24,402,000
Unrecognized tax benefits	0	0
Domestic Tax Authority [Member]
Tax Credit Carryforward [Line Items]
Net operating loss carryforwards for federal and state income tax, expiration period	2024
Research and development tax credit carryforwards for federal and state income tax purposes	809,000
Domestic Tax Authority [Member] | Research Tax Credit Carryforward [Member]
Tax Credit Carryforward [Line Items]
Research and development tax credit carryforwards for federal and state income tax purposes, expiration period	2025
State and Local Jurisdiction [Member]
Tax Credit Carryforward [Line Items]
Net operating loss carryforwards for federal and state income tax, expiration period	2030
Research and development tax credit carryforwards for federal and state income tax purposes	$302,000
State and Local Jurisdiction [Member] | Research Tax Credit Carryforward [Member]
Tax Credit Carryforward [Line Items]
Research and development tax credit carryforwards for federal and state income tax purposes, expiration period	2023

Income_Taxes_Reconciliation_of

Income Taxes - Reconciliation of U.S. Federal Statutory Income Tax Rate (Detail)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Income Tax Disclosure [Abstract]
Federal statutory income tax rate	-34.00%	-34.00%	-34.00%
Federal research and development tax credit	-0.90%	-0.70%	-1.20%
State taxes, net of federal benefit	-4.50%	-5.60%	-5.40%
Stock-based compensation expense	1.10%	0.40%	0.60%
Other	0.20%	0.10%
Change in deferred tax asset valuation allowance	38.10%	39.80%	40.00%
Effective income tax rate	0.00%	0.00%	0.00%

Income_Taxes_Schedule_of_Net_D

Income Taxes - Schedule of Net Deferred Tax Assets (Detail) (USD $)	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
In Thousands, unless otherwise specified
Current deferred tax assets:
Accrued expenses	$414	$201
Total current deferred tax assets	414	201
Noncurrent deferred tax assets:
Capitalized research and development expenses	24,945	19,250
Net operating loss carryforwards	6,292	3,989
Research and development tax credit carryforwards	1,008	889
Other	613	73
Total noncurrent deferred tax assets	32,858	24,201
Total gross deferred tax assets	33,272	24,402
Valuation allowance	-33,272	-24,402	-18,138	-14,129
Net deferred tax assets	$0	$0

Income_Taxes_Summary_of_Change

Income Taxes - Summary of Changes in Valuation Allowance for Deferred Tax Assets (Detail) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Income Tax Disclosure [Abstract]
Valuation allowance, beginning balance	$24,402	$18,138	$14,129
Decreases recorded as benefit to income tax provision	0	0	0
Increases recorded to income tax provision	8,870	6,264	4,009
Valuation allowance, ending balance	$33,272	$24,402	$18,138

Related_Party_Transactions_Add

Related Party Transactions - Additional Information (Detail) (Former Advisor [Member], USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2007
Former Advisor [Member]
Schedule of Other Related Party Transactions [Line Items]
Outstanding loans from related party transaction	$250,000
Interest rate	2.92%
Loan made to related party			220,000
Other income	158,000
Payments from loans receivable	$158,000	$0

Selected_Quarterly_Financial_D2

Selected Quarterly Financial Data (Unaudited) - Schedule of Selected Quarterly Financial Data (Detail) (USD $)	3 Months Ended								12 Months Ended
In Thousands, except Per Share data, unless otherwise specified	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Quarterly Financial Information Disclosure [Abstract]
Revenue	$0	$0	$0	$0	$0	$0	$0	$0	$0	$0	$0
Loss from operations	-6,261	-6,424	-5,885	-4,892	-5,549	-3,365	-4,444	-2,391	-23,462	-15,749	-9,649
Net loss	-6,208	-6,390	-5,851	-4,847	-5,525	-3,365	-4,445	-2,390	-23,296	-15,725	-9,649
Net loss attributable to common stockholders	($6,208)	($6,390)	($5,851)	($4,847)	($5,540)	($3,365)	($4,524)	($2,390)	($23,296)	($15,819)	($9,683)
Basic and diluted net loss attributable to common stockholders per share	($0.28)	($2.71)	($11.68)	($9.79)	($11.23)	($6.82)	($12.95)	($7.20)	($3.60)	($38.02)	($31.09)