Larimar Therapeutics (LRMR) S-112 Jan 15IPO registrationFinancial data

Company Profile

Document_and_Entity_Informatio

Document and Entity Information	9 Months Ended
Document and Entity Information	Sep. 30, 2014
Document And Entity Information [Abstract]
Document Type	S-1
Amendment Flag	FALSE
Document Period End Date	30-Sep-14
Trading Symbol	ZFGN
Entity Registrant Name	Zafgen, Inc.
Entity Central Index Key	1374690
Entity Filer Category	Non-accelerated Filer

Consolidated_Balance_Sheets

Consolidated Balance Sheets (USD $)	Sep. 30, 2014	Dec. 31, 2013	Dec. 31, 2012
In Thousands, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013	Dec. 31, 2012
Current assets:
Cash and cash equivalents	$127,030	$35,517	$9,935
Prepaid expenses and other current assets	1,221	224	389
Tax incentive receivable	1,218	1,617
Total current assets	129,469	37,358	10,324
Tax incentive receivable			630
Property and equipment, net	69	37	32
Other assets	98	743
Total assets	129,636	38,138	10,986
Current liabilities:
Accounts payable	1,052	2,015	1,231
Accrued expenses	9,885	900	1,699
Notes payable, current	684
Total current liabilities	11,621	2,915	2,930
Notes payable, net of discount, long-term	6,819
Total liabilities	18,440	2,915	2,930
Commitments and contingencies
Redeemable convertible preferred stock (Series A, B, C, D and E),		103,797	62,785
Stockholders' equity (deficit):
Preferred stock
Common stock	23	1	1
Additional paid-in capital	205,627	332	150
Accumulated deficit	-94,454	-68,907	-54,880
Total stockholders' deficit	111,196	-68,574	-54,729
Total liabilities, redeemable convertible preferred stock and stockholders' deficit	$129,636	$38,138	$10,986

Consolidated_Balance_Sheets_Pa

Consolidated Balance Sheets (Parenthetical) (USD $)	Sep. 30, 2014	Dec. 31, 2013	Dec. 31, 2012
In Thousands, except Share data, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013	Dec. 31, 2012
Statement of Financial Position [Abstract]
Redeemable convertible preferred stock (Series A, B, C, D and E), par value	$0.00	$0.00	$0.00
Redeemable convertible preferred stock (Series A, B, C, D and E), shares authorized	0	99,292,610	78,372,931
Redeemable convertible preferred stock (Series A, B, C, D and E), shares issued	0	94,483,404	73,991,017
Redeemable convertible preferred stock (Series A, B, C, D and E), shares outstanding	0	94,483,404	73,991,017
Redeemable convertible preferred stock (Series A, B, C, D and E), aggregate liquidation preference value		$104,588	$63,629
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	$0.00
Common stock, shares authorized	115,000,000	115,000,000	100,000,000
Common stock, shares issued	22,707,012	729,391	736,026
Common stock, shares outstanding	22,707,012	729,391	736,026

Consolidated_Statements_of_Ope

Consolidated Statements of Operations and Comprehensive Loss (USD $)	9 Months Ended		12 Months Ended
In Thousands, except Share data, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Income Statement [Abstract]
Revenue	$0	$0	$0	$0	$0
Operating expenses:
Research and development	20,046	7,038	9,561	11,544	11,403
General and administrative	4,822	2,981	4,219	2,247	1,751
Total operating expenses	24,868	10,019	13,780	13,791	13,154
Loss from operations	-24,868	-10,019	-13,780	-13,791	-13,154
Other income (expense):
Interest income	2
Interest expense	-658			-97
Foreign currency transaction gains (losses), net	-23	-162	-247	8	-3
Total other expense, net	-679	-162	-247	-89	-3
Net loss and comprehensive loss	-25,547	-10,181	-14,027	-13,880	-13,157
Accretion of redeemable convertible preferred stock to redemption value	-92	-160	-213	-67	-53
Net loss attributable to common stockholders	($25,639)	($10,341)	($14,240)	($13,947)	($13,210)
Net loss per share attributable to common stockholders, basic and diluted	($2.97)	($14.19)	($19.53)	($19.65)	($19.17)
Weighted average common shares outstanding, basic and diluted	8,618,793	728,862	729,001	709,678	688,946

Consolidated_Statements_of_Red

Consolidated Statements of Redeemable Convertible Preferred Stock and Stockholders' Deficit (USD $)	Total	Series B Preferred Stock [Member]	Series C Preferred Stock [Member]	Series D Preferred Stock [Member]	Series E Preferred Stock [Member]	Redeemable convertible preferred stock [Member]	Redeemable convertible preferred stock [Member]	Redeemable convertible preferred stock [Member]	Redeemable convertible preferred stock [Member]	Redeemable convertible preferred stock [Member]	Common Stock [Member]	Additional Paid-in Capital [Member]	Accumulated Deficit [Member]
In Thousands, except Share data	USD ($)					USD ($)	Series B Preferred Stock [Member]	Series C Preferred Stock [Member]	Series D Preferred Stock [Member]	Series E Preferred Stock [Member]	USD ($)	USD ($)	USD ($)
							USD ($)	USD ($)	USD ($)	USD ($)
Temporary equity, beginning balance at Dec. 31, 2010						$30,453
Beginning balance at Dec. 31, 2010	-27,786										1	56	-27,843
Temporary equity, beginning balance, shares at Dec. 31, 2010						42,947,474
Beginning balance, shares at Dec. 31, 2010											719,957
Issuance of redeemable convertible preferred stock, value							2,016	8,053
Issuance of redeemable convertible preferred stock, shares							2,682,011	8,923,884
Stock-based compensation expense	80											80
Accretion of redeemable convertible preferred stock to redemption value	-53					53						-53
Net loss	-13,157												-13,157
Temporary equity, ending balance at Dec. 31, 2011						40,575
Ending balance at Dec. 31, 2011	-40,916										1	83	-41,000
Temporary equity, ending balance, shares at Dec. 31, 2011						54,553,369
Beginning balance, shares at Dec. 31, 2011											719,957
Issuance of redeemable convertible preferred stock, value								7,067	8,990
Issuance of redeemable convertible preferred stock, shares								7,808,400	6,653,988
Conversion of promissory notes and accrued interest to convertible preferred stock, value									6,086
Conversion of promissory notes and accrued interest to convertible preferred stock, shares									4,975,260
Issuance of common stock upon exercise of stock options, value	13											13
Issuance of common stock upon exercise of stock options, shares	16,069										16,069
Stock-based compensation expense	121											121
Accretion of redeemable convertible preferred stock to redemption value	-67					67						-67
Net loss	-13,880												-13,880
Temporary equity, ending balance at Dec. 31, 2012	62,785					62,785
Ending balance at Dec. 31, 2012	-54,729										1	150	-54,880
Temporary equity, ending balance, shares at Dec. 31, 2012	73,991,017	40,266,246	16,732,284	11,629,248		73,991,017
Ending balance, shares at Dec. 31, 2012											736,026
Issuance of redeemable convertible preferred stock, value									5,955	34,844
Repurchase and retirement of common stock, at cost											-6,635
Issuance of redeemable convertible preferred stock, shares									4,381,914	16,110,473
Stock-based compensation expense	395											395
Accretion of redeemable convertible preferred stock to redemption value	-213					213						-213
Net loss	-14,027												-14,027
Temporary equity, ending balance at Dec. 31, 2013	103,797					103,797
Ending balance at Dec. 31, 2013	($68,574)										$1	$332	($68,907)
Temporary equity, ending balance, shares at Dec. 31, 2013	94,483,404	40,266,246	16,732,284	16,011,162	16,110,473	94,483,404
Ending balance, shares at Dec. 31, 2013											729,391

Consolidated_Statements_of_Red1

Consolidated Statements of Redeemable Convertible Preferred Stock and Stockholders' Deficit (Parenthetical) (USD $)	9 Months Ended		12 Months Ended		1 Months Ended	12 Months Ended	1 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013	Dec. 31, 2013	Dec. 31, 2011	Feb. 29, 2012	Dec. 31, 2012	Jan. 31, 2013	Nov. 30, 2012	Nov. 30, 2013
Issuance of redeemable convertible preferred stock, issuance costs	$2,312	$165	$196
Series B Preferred Stock [Member]
Issuance of redeemable convertible preferred stock, issuance costs				9
Series C Preferred Stock [Member]
Issuance of redeemable convertible preferred stock, issuance costs				33	8	8
Series D Preferred Stock [Member]
Issuance of redeemable convertible preferred stock, issuance costs			1			54	1	54
Series E Preferred Stock [Member]
Issuance of redeemable convertible preferred stock, issuance costs			$156						$156

Consolidated_Statements_of_Cas

Consolidated Statements of Cash Flows (USD $)	9 Months Ended		12 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Cash flows from operating activities:
Net loss	($25,547)	($10,181)	($14,027)	($13,880)	($13,157)
Adjustments to reconcile net loss to net cash used in operating activities
Stock-based compensation expense	910	252	395	121	80
Non-cash interest expense	36			97
Depreciation expense	10	8	12	11	4
Unrealized foreign currency transaction losses	31	169	250
(Gain) loss on disposal of property and equipment					-2
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	-997	160	165	-269	-61
Tax incentive receivable	368	-1,230	-1,237	-630
Accounts payable	-416	122	237	727	-43
Accrued expenses	9,078	-171	-799	234	905
Net cash used in operating activities	-16,527	-10,871	-15,004	-13,589	-12,274
Cash flows from investing activities:
Purchases of property and equipment	-42	-9	-17	-2	-35
Proceeds from sales of property and equipment					2
Deposits for leased property	-57				-12
Net cash used in investing activities	-99	-9	-17	-2	-45
Cash flows from financing activities:
Proceeds from issuance of redeemable convertible preferred stock, net of issuance costs	442	5,955	40,799	16,057	10,069
Issuance of convertible promissory notes, net of issuance costs	7,386			5,989
Payments of debt offering costs	-49
Proceeds from exercise of common stock options				13
Proceeds from initial public offering costs, net of underwriting commissions and discounts	102,672
Payments of initial public offering costs	-2,312	-165	-196
Net cash provided by financing activities	108,139	5,790	40,603	22,059	10,069
Net increase (decrease) in cash and cash equivalents	91,513	-5,090	25,582	8,468	-2,250
Cash and cash equivalents at beginning of period	35,517	9,935	9,935	1,467	3,717
Cash and cash equivalents at end of period	127,030	4,845	35,517	9,935	1,467
Supplemental disclosure of non-cash investing and financing activities:
Accretion of redeemable convertible preferred stock to redemption values	92	160	213	67	53
Deferred offering costs and deferred financing costs included in accounts payable and accrued expenses		14	547
Conversion of convertible promissory notes and accrued interest to shares of redeemable convertible preferred stock	104,331			6,086
Supplemental disclosure of cash flow information:
Cash paid for interest	$480

Nature_of_the_Business_and_Bas

Nature of the Business and Basis of Presentation	9 Months Ended	12 Months Ended
Nature of the Business and Basis of Presentation	Sep. 30, 2014	Dec. 31, 2013
Accounting Policies [Abstract]
Nature of the Business and Basis of Presentation	1. Nature of the Business and Basis of Presentation	1. Nature of the Business and Basis of Presentation
	Zafgen, Inc. (the “Company”) was incorporated on November 22, 2005 under the laws of the State of Delaware. The Company is a biopharmaceutical company dedicated to significantly improving the health and well-being of patients affected by obesity. Beloranib, the Company’s lead product candidate, is a novel, first-in-class, twice-weekly subcutaneous injection being developed for the treatment of multiple indications, including obesity and hyperphagia in Prader-Willi syndrome patients, hypothalamic injury-associated obesity including craniopharyngioma-associated obesity, and severe obesity in the general population. Since its inception, the Company has devoted substantially all of its efforts to research and development, recruiting management, acquiring operating assets and raising capital.	Zafgen, Inc. (the “Company”) was incorporated on November 22, 2005 under the laws of the State of Delaware. The Company is a biopharmaceutical company dedicated to significantly improving the health and well-being of patients affected by obesity. Beloranib, the Company’s lead product candidate, is a novel, first-in-class, twice-weekly subcutaneous injection being developed for the treatment of multiple indications, including obesity and hyperphagia in Prader-Willi Syndrome patients, craniopharyngioma-associated obesity, and severe obesity in the general population. Since its inception, the Company has devoted substantially all of its efforts to research and development, recruiting management, acquiring operating assets and raising capital.
	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. Product candidates currently under development will require significant additional research and development efforts, including extensive pre-clinical 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.	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. Product candidates currently under development will require significant additional research and development efforts, including extensive pre-clinical 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.
	The Company’s product candidates are all in the development stage. 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 product 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 Company’s product candidates are all in the development stage. 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 product 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 consolidated financial statements include the accounts of the Company and its wholly owned subsidiaries Zafgen Securities Corporation, Zafgen Australia Pty Limited, and Zafgen Animal Health, LLC. All significant intercompany balances and transactions have been eliminated.	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 experienced negative cash flows and has an accumulated deficit of $68,907 as of December 31, 2013. The Company expects that its existing cash and cash equivalents as of December 31, 2013 will enable the Company to fund its operating expenses and capital expenditure requirements for at least twelve months from the balance sheet date. The future viability of the Company is largely dependent on its ability to generate cash from operating activities or to raise additional capital to finance its operations. The Company’s failure to raise capital as and when needed could have a negative impact on its financial condition and ability to pursue its business strategies.
	The accompanying consolidated financial statements have been prepared in conformity with accounting principles generally accepted in the United States of America (“GAAP”).	The Company is seeking to complete an initial public offering of its common stock. Upon a successful qualified public offering with net proceeds of not less than $35,000, the Company’s outstanding redeemable convertible preferred stock will automatically convert into shares of common stock.
	On June 24, 2014, the Company completed an initial public offering (“IPO”) of its common stock, which resulted in the sale of 6,900,000 shares at a price of $16.00 per share. The Company received net proceeds from the IPO of approximately $102,672 based upon the price of $16.00 per share and after deducting underwriting discounts and commissions paid by the Company. The Company also incurred offering costs of $2,508 related to the IPO.	In the event the Company does not complete an initial public offering, the Company expects to seek additional funding through private financings, debt financing, collaboration agreements or government grants. The Company may not be able to obtain financing on acceptable terms, or at all, and the Company may not be able to enter into collaboration arrangements or obtain government grants. The terms of any financing may adversely affect the holdings or the rights of the Company’s stockholders. If the Company is unable to obtain funding, the Company could be forced to delay, reduce or eliminate its research and development programs, product portfolio expansion or commercialization efforts, which could adversely affect its business prospects. Although management continues to pursue these plans, there is no assurance that the Company will be successful in obtaining sufficient funding on terms acceptable to the Company to fund continuing operations, if at all.
	Unaudited Interim Financial Information	The consolidated financial statements include the accounts of the Company and its wholly owned subsidiaries, Zafgen Securities Corporation, Zafgen Australia Pty Limited, and Zafgen Animal Health, LLC. All significant intercompany balances and transactions have been eliminated.
	The consolidated balance sheet at December 31, 2013 was derived from audited financial statements, but does not include all disclosures required by GAAP. The accompanying unaudited consolidated financial statements as of September 30, 2014, and for the nine months ended September 30, 2014 and 2013, have been prepared by the Company, pursuant to the rules and regulations of the SEC for interim financial statements. Certain information and footnote disclosures normally included in financial statements prepared in accordance with GAAP have been condensed or omitted pursuant to such rules and regulations. However, the Company believes that the disclosures are adequate to make the information presented not misleading. These consolidated financial statements should be read in conjunction with the Company’s audited consolidated financial statements and the notes thereto for the year ended December 31, 2013. In the opinion of management, all adjustments, consisting only of normal recurring adjustments necessary for a fair statement of the Company’s consolidated financial position as of September 30, 2014 and consolidated results of operations and consolidated cash flows for the nine months ended September 30, 2014 and 2013 have been made. The results for the nine months ended September 30, 2014 are not necessarily indicative of the results that may be expected for the year ending December 31, 2014, any other interim periods, or any future year or period.	The accompanying consolidated financial statements have been prepared in conformity with accounting principles generally accepted in the United States of America (“GAAP”).

Summary_of_Significant_Account

Summary of Significant Accounting Policies

9 Months Ended

12 Months Ended

Sep. 30, 2014

Dec. 31, 2013

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 and assumptions that affect the reported amounts of assets and liabilities, the disclosure of contingent assets and liabilities at the date of the consolidated financial statements, and the reported amounts of expenses during the reporting periods. Significant estimates and assumptions reflected in these consolidated financial statements include, but are not limited to, the accrual of research and development expenses and the valuation of common stock prior to the IPO and 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.

The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, the disclosure of contingent assets and liabilities at the date of the consolidated financial statements, and the reported amounts of expenses during the reporting periods. Significant estimates and assumptions reflected in these consolidated financial statements include, but are not limited to, the accrual of research and development expenses and the valuation of common stock and 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 acquisition date 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 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 $100,000 and $26,501 as of September 30, 2014 and December 31, 2013, respectively, were carried at fair value based on quoted prices in active markets, a Level 1 measurement. The carrying values of accounts payable and accrued expenses approximate their fair value due to the short-term nature of these liabilities. The Company’s carrying value of outstanding debt issued in the first quarter of 2014 approximates fair value based on the recent execution date of the credit facility agreement, and is considered a Level 2 measurement.

The Company’s cash equivalents of $8,001 as of December 31, 2012 and $26,501 as of December 31, 2013 were carried at fair value based on quoted prices in active markets, a Level 1 measurement. 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 $743 of deferred offering costs, included in other assets in the accompanying consolidated balance sheet, in contemplation of the Company’s IPO of its common stock, which closed in June 2014. The Company has no deferred offering costs as of September 30, 2014.

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 recorded $743 of deferred offering costs, included in other assets in the accompanying consolidated balance sheet, in contemplation of a probable 2014 equity financing. Should the equity financing no longer be considered probable of being consummated, the deferred offering costs would be expensed immediately as a charge to operating expenses in the consolidated statement of operations. The Company did not record any deferred offering costs as of December 31, 2012.

Property and Equipment

Property and equipment are stated at cost less accumulated depreciation. Depreciation expense is recognized using the straight-line method over a five-year estimated useful life for both furniture and fixtures and office equipment. 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 wages, stock-based compensation and benefits of employees, third-party license fees and milestones and other operational costs related to the Company’s research and development activities, including facility-related expenses and external costs of outside vendors engaged to conduct both pre-clinical studies and clinical trials. The Company records research and development expenses net of any research and development tax incentives the Company is entitled to receive from government authorities.

Research and development costs are expensed as incurred. Included in research and development expenses are wages, stock-based compensation and benefits of employees, third-party license fees and other operational costs related to the Company’s research and development activities, including facility-related expenses and external costs of outside vendors engaged to conduct both pre-clinical studies and clinical trials. The Company records research and development expenses net of any research and development tax incentives the Company is entitled to receive from government authorities.

Research Contract Costs and Accruals

The Company has entered into various research and development contracts with research institutions and other companies both inside and outside of the United States. These agreements are generally cancelable, and related payments are recorded as research and development expenses as incurred. The Company records accruals for estimated ongoing research costs. When evaluating the adequacy of the accrued liabilities, the Company analyzes progress of the studies, including the phase or completion of events, invoices received and contracted costs. Significant judgments and estimates are made in determining the accrued balances at the end of any reporting period. Actual results could differ from the Company’s estimates. The Company’s historical accrual estimates have not been materially different from the actual 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

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.

For stock-based awards granted to consultants and nonemployees, compensation expense is recognized over the period during which services are rendered by such consultants and nonemployees until completed. At the end of each financial reporting period prior to completion of the service, the fair value of these 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 recipients’ 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 advancing novel therapeutics for patients suffering from severe obesity and obesity-related disorders. 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, 2011, 2012 and 2013, there was no difference between net loss and 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 nine months ended September 30, 2014 and 2013, there was no difference between net loss and comprehensive loss.

Net Income (Loss) Per Share

The Company follows the two-class method when computing net income (loss) per share, as the Company has issued shares that meet 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.

Net Income (Loss) Per Share

Upon the closing of the Company’s IPO in June 2014, all of the Company’s outstanding redeemable convertible preferred shares were converted into shares of 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 meet 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 shareholders for the period to be allocated between common and participating securities based upon their respective rights to receive dividends as if all income for the period had been distributed. The Company’s redeemable convertible preferred shares 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 shareholders resulting from dividends or accretion related to its redeemable convertible preferred shares.

Basic net income (loss) per share attributable to common stockholders is computed by dividing the net income (loss) attributable to common stockholders by the weighted average number of shares of common stock outstanding for the period. Diluted net income (loss) attributable to common stockholders is computed by adjusting income (loss) attributable to common stockholders to reallocate undistributed earnings based on the potential impact of dilutive securities, including outstanding stock options and unvested restricted common stock. Diluted net income (loss) per share attributable to common stockholders is computed by dividing the diluted net income (loss) attributable to common stockholders by the weighted average number of common shares outstanding for the period, including potential dilutive common shares assuming the dilutive effect of outstanding stock options and unvested restricted common stock.

Basic net income (loss) per share attributable to common shareholders is computed by dividing the net income (loss) attributable to common shareholders by the weighted average number of common shares outstanding for the period. Diluted net income (loss) per share attributable to common shareholders is computed by dividing the diluted net income (loss) attributable to common shareholders 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 shareholders is the same as basic net loss per common share attributable to common shareholders, since dilutive common shares are not assumed to have been issued if their effect is antidilutive.

The Company’s redeemable convertible preferred stock contractually entitles the holders of such shares to participate in dividends but does not contractually require the holders of such shares to participate in losses of the Company. Similarly, restricted stock awards granted by the Company entitle the holder of such awards to dividends declared or paid by the board of directors, regardless of whether such awards are unvested, as if such shares were outstanding common shares at the time of the dividend. However, the unvested restricted stock awards are not entitled to share in the residual net assets (deficit) of the Company. Accordingly, in periods in which the Company reports a net loss attributable to common stockholders, diluted net loss per share attributable to common stockholders is the same as basic net loss per share attributable to common stockholders, since dilutive common shares are not assumed to have been issued if their effect is anti-dilutive. The Company reported a net loss attributable to common stockholders for the years ended December 31, 2011, 2012 and 2013.

The Company reported a net loss attributable to common stockholders for the nine months ended September 30, 2014 and 2013.

Recently Issued and Adopted Accounting Pronouncements

The following common stock equivalents, outstanding as of September 30, 2014 and 2013, were excluded from the computation of diluted net loss per share for the nine months ended September 30, 2014 and 2013 because they had an anti-dilutive impact:

In June 2011, the Financial Accounting Standards Board (“FASB”) issued an amendment to the accounting guidance for presentation of comprehensive income. Under the amended guidance, a company may present the total of comprehensive income, the components of net income, and the components of other comprehensive income either in a single continuous statement of comprehensive income or in two separate but consecutive statements. In either case, a company is required to present each component of net income along with total net income, each component of other comprehensive income along with a total for other comprehensive income, and a total amount for comprehensive income. The amendment is effective for fiscal years ending, and interim periods within those years, beginning after December 15, 2011, and is applied retrospectively. The Company adopted this amendment in the accompanying consolidated financial statements by presenting comprehensive loss in a single continuous statement along with net loss.

In June 2014, the FASB issued Accounting Standards Update (“ASU”) No. 2014-10, Development Stage Entities. The amendments in this guidance remove all incremental financial reporting requirements for development stage entities. Among other changes, this guidance no longer requires 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. Early application is permitted for interim and annual periods for which financial statements have not yet been issued. The Company early adopted this guidance in the three months ended June 30, 2014 and, as a result, no longer discloses inception-to-date information in its consolidated statements of operations and comprehensive loss, cash flows and stockholders’ deficit and the related notes thereto.

As of September 30,

Accounting standards that have been issued or proposed by the FASB or other standards-setting bodies that do not require adoption until a future date are not expected to have a material impact on the Company’s consolidated financial statements upon adoption.

2014

2013

Options to purchase common stock

1,839,895

1,283,264

Redeemable convertible preferred stock

—

78,372,931

Total options and redeemable convertible preferred stock exercisable or convertible into common stock

1,839,895

79,656,195

Recently Issued and Adopted Accounting Pronouncements

In June 2014, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) No. 2014-10, Development Stage Entities. 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. Early application is permitted for interim and annual periods for which financial statements have not yet been issued. The Company early adopted this guidance in the three months ended June 30, 2014 and, as a result, no longer discloses inception-to-date information in its consolidated statements of operations and comprehensive loss, cash flows and stockholders’ deficit and the related notes thereto.

In August 2014, the FASB issued ASU No. 2014-15, Presentation of Financial Statements — Going Concern. 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
Property and Equipment, net	Dec. 31, 2013
Property, Plant and Equipment [Abstract]
Property and Equipment, net	3. Property and Equipment, net
	Property and equipment, net consisted of the following as of December 31, 2012 and 2013:


		December 31,
		2012			2013
	Office equipment	$	10		$	27
	Furniture and fixtures		44			44

			54			71
	Less: Accumulated depreciation		(22	)		(34	)

		$	32		$	37

	Depreciation expense was $4, $11 and $12 for the years ended December 31, 2011, 2012 and 2013, respectively.

Accrued_Expenses

Accrued Expenses	9 Months Ended					12 Months Ended
Accrued Expenses	Sep. 30, 2014					Dec. 31, 2013
Payables and Accruals [Abstract]
Accrued Expenses	3. Accrued Expenses					4. Accrued Expenses
	Accrued expenses consisted of the following:					Accrued expenses consisted of the following as of December 31, 2012 and 2013:


		September 30,		December 31,			December 31,
		2014		2013			2012		2013
	Accrued licensing milestone fees	$	6,700	$	—	Accrued payroll and related expenses	$	74	$	49
	Accrued research and development expenses		1,759		616	Accrued research and development expenses		1,558		616
	Accrued payroll and related expenses		741		49	Accrued professional fees		62		196
	Accrued professional fees		542		196	Accrued other		5		39
	Accrued interest		51		—
	Accrued other		92		39		$	1,699	$	900

		$	9,885	$	900

Convertible_Promissory_Notes

Convertible Promissory Notes	9 Months Ended			12 Months Ended
Convertible Promissory Notes	Sep. 30, 2014			Dec. 31, 2013
Debt Disclosure [Abstract]
Convertible Promissory Notes	4. Notes Payable			5. Convertible Promissory Notes
	On March 31, 2014, the Company entered into a loan and security agreement with Oxford Finance LLC and Midcap Financial (the “Credit Facility”). The Credit Facility provides for initial borrowings of $7,500 under a term loan (“Term Loan A”) and additional borrowings of up to $12,500 under other term loans, for a maximum of $20,000. On March 31, 2014, the Company received proceeds of $7,500 from the issuance of promissory notes under the Term Loan A. Of the additional $12,500 amount that was available, $7,500 (“Term Loan B”) was available to be drawn down until September 30, 2014 and $5,000 (“Term Loan C”) was available to be drawn down for a 30-day period upon the completion of the Company’s IPO that occurred in June 2014. The Company elected not to draw down Term Loan B or Term Loan C and these amounts are no longer available to the Company. All promissory notes issued under the Credit Facility are collateralized by substantially all of the Company’s personal property, other than its intellectual property.			In August and November 2012, the Company issued convertible promissory notes with a principal amount of $6,000. The notes accrued interest at an annual rate of 8% and, unless otherwise converted, were due one year from the issuance date. The notes were to be automatically converted into shares of a new class of preferred stock upon the sale by the Company of the new class of preferred stock yielding proceeds of at least $10,000 or, if the sale of the new class of preferred stock was for less than $10,000, the notes could be converted at the option of the noteholder at 90% of the price of the new series of preferred stock. In November 2012, upon the Company’s issuance of 6,653,988 shares of Series D redeemable convertible preferred stock for gross proceeds of $9,044 (see Note 6), the noteholders elected to convert the outstanding principal and accrued interest of $6,086 into 4,975,260 shares of Series D redeemable convertible preferred stock.
	Upon entering into this Credit Facility, the Company was obligated to make monthly, interest-only payments on any term loans funded under the Credit Facility until December 1, 2014 and, thereafter, to pay 36 consecutive, equal monthly installments of principal and interest from January 1, 2015 through December 1, 2017. As per the terms of the agreement, in June 2014, upon the completion of the Company’s IPO, the term of monthly, interest-only payments were extended until June 1, 2015. Outstanding term loans under the Credit Facility bear interest at an annual rate of 8.1%. In addition, a final payment equal to 6.0% of any amounts drawn under the Credit Facility is due upon the earlier of the maturity date, acceleration of the term loans or prepayment of all or part of the term loans. The Company accrues the amount due relating to Term Loan A of $450, to outstanding debt by charges to interest expense using the effective-interest method from the date of issuance through the maturity date.
	Term Loan A was recorded in the balance sheet net of debt discount of $114 that was related to fees assessed by the lender at the time of borrowing. The debt discount is being accreted to the principal amount of the debt. In addition, deferred financing costs of $49 are being amortized to interest expense using the effective-interest method over the same term. For the nine months ended September 30, 2014, the Company recorded additional interest expense of $36 related the accretion of the debt discount and amortization of deferred financing costs.
	The Company was obligated to pay a separate fee upon any IPO; a sale of substantially all of the Company’s assets; or a merger, reorganization or sale of the Company’s voting equity securities where existing voting stockholders hold less than 50% of voting equity securities after such transaction. As of September 30, 2014, the Company recorded interest expense of $225 relating to the fee payable upon completion of the Company’s IPO in June 2014.
	There are no financial covenants associated with the debt facility; however, there are negative covenants restricting the Company’s activities, including limitations on dispositions, mergers or acquisitions; encumbering or granting a security interest in its intellectual property; incurring indebtedness or liens; paying dividends; making certain investments; and certain other business transactions.
	The Credit Facility also includes events of default, the occurrence and continuation of any of which provides the lenders the right to exercise remedies against the Company and the collateral securing the loans under the Credit Facility, including cash. These events of default include, among other things, failure to pay any amounts due under the Credit Facility, insolvency, the occurrence of a material adverse event, the occurrence of any default under certain other indebtedness and a final judgment against the Company in an amount greater than $250.
	Estimated future principal payments due under the Term Loan A are as follows:


	Years Ending December 31,
	Remainder of 2014	$	—
	2015		1,381
	2016		2,936
	2017		3,183

	Total	$	7,500

	During the nine months ended September 30, 2014, the Company recognized $658 of interest expense related to the Credit Facility.
	The Company had no debt outstanding as of December 31, 2013.

Redeemable_Convertible_Preferr

Redeemable Convertible Preferred Stock	12 Months Ended
Redeemable Convertible Preferred Stock	Dec. 31, 2013
Equity [Abstract]
Redeemable Convertible Preferred Stock	6. Redeemable Convertible Preferred Stock
	As of December 31, 2013, the Company’s Certificate of Incorporation, as amended and restated, authorizes the Company to issue 99,292,610 shares of $0.001 par value preferred stock.
	The Company has issued Series A, Series B, Series C, Series D and Series E redeemable convertible preferred stock (collectively, the “Redeemable Preferred Stock”). The Redeemable Preferred Stock is classified outside of stockholders’ equity (deficit) because the shares contain redemption features that are not solely within the control of the Company.
	In June and December 2011, the Company issued a total of 8,923,884 shares of Series C redeemable convertible preferred stock at an issuance price equal to $0.9061 per share and received gross proceeds of $8,086. In connection with this financing, the Company paid total issuance costs of $33.
	In February 2012, the Company issued 7,808,400 shares of Series C redeemable convertible preferred stock at an issuance price equal to $0.9061 per share and received gross proceeds of $7,075. In connection with this financing, the Company paid total issuance costs of $8.
	In November 2012, the Company issued 6,653,988 shares of Series D redeemable convertible preferred stock at an issuance price equal to $1.3592 per share and received gross proceeds of $9,044. In connection with this financing, the Company paid total issuance costs of $54. Additionally, in November 2012, $6,000 of convertible promissory notes and $86 of accrued interest were converted into 4,975,260 shares of Series D redeemable convertible preferred stock (see Note 5).
	In January 2013, the Company issued 4,381,914 shares of Series D redeemable convertible preferred stock at an issuance price equal to $1.3592 per share and received gross proceeds of $5,956. In connection with this financing, the Company paid total issuance costs of $1.
	In November 2013, the Company issued 16,110,473 shares of Series E redeemable convertible preferred stock at an issuance price equal to $2.1725 per share and received gross proceeds of $35,000. In connection with this financing, the Company paid total issuance costs of $156.
	Redeemable Preferred Stock consisted of the following as of December 31, 2012:


		Preferred		Preferred		Liquidation		Carrying		Common
		Shares		Shares		Preference		Value		Stock Issuable
		Authorized		Issued and						Upon
				Outstanding						Conversion
	Series A redeemable convertible preferred stock		5,363,239		5,363,239	$	2,250	$	2,222		854,018
	Series B redeemable convertible preferred stock		40,266,246		40,266,246		30,402		30,335		6,411,822
	Series C redeemable convertible preferred stock		16,732,284		16,732,284		15,161		15,137		2,664,376
	Series D redeemable convertible preferred stock		16,011,162		11,629,248		15,816		15,091		1,851,791

			78,372,931		73,991,017	$	63,629	$	62,785		11,782,007

	Redeemable Preferred Stock consisted of the following as of December 31, 2013:


		Preferred		Preferred		Liquidation		Carrying		Common
		Shares		Shares		Preference		Value		Stock Issuable
		Authorized		Issued and						Upon
				Outstanding						Conversion
	Series A redeemable convertible preferred stock		5,363,239		5,363,239	$	2,250	$	2,229		854,018
	Series B redeemable convertible preferred stock		40,266,246		40,266,246		30,402		30,351		6,411,822
	Series C redeemable convertible preferred stock		16,732,284		16,732,284		15,161		15,144		2,664,376
	Series D redeemable convertible preferred stock		16,011,162		16,011,162		21,775		21,226		2,549,548
	Series E redeemable convertible preferred stock		20,919,679		16,110,473		35,000		34,847		2,565,361

			99,292,610		94,483,404	$	104,588	$	103,797		15,045,125


	The holders of the Redeemable Preferred Stock have the following rights and preferences:
	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 have 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.
	Dividends
	The Company may not declare, pay or set aside any dividends on shares of any other class or series of capital stock of the Company unless the holders of the Redeemable Preferred Stock then outstanding shall first receive a dividend on each outstanding share of Redeemable Preferred Stock in an amount at least equal to (i) in the case of a dividend on common stock or any class or series that is convertible into common stock, that dividend per share of Redeemable Preferred Stock as would equal the product of (A) the dividend payable on each share of such class or series determined, if applicable, as if all shares of such class or series had been converted into common stock and (B) the number of shares of common stock issuable upon conversion of a share of Redeemable Preferred Stock, or (ii) in the case of a dividend on any class or series that is not convertible into common stock, at a rate per share of Redeemable Preferred Stock determined by (A) dividing the amount of the dividend payable on each share of such class or series of capital stock by the original issuance price of such class or series of capital stock (subject to appropriate adjustment in the event of any stock dividend, stock split, combination of or other similar recapitalization affecting such shares) and (B) multiplying such fraction by an amount equal to the Original Issue Price (as defined below) of each series of Redeemable Preferred Stock. If the Company declares, pays or sets aside, on the same date, a dividend on shares of more than one class or series of capital stock of the Company, the dividend payable to the holders of the Redeemable Preferred Stock shall be calculated based upon the dividend on the class or series of capital stock that would result in the highest Redeemable Preferred Stock dividend. The Original Issue Price for Series A, Series B, Series C, Series D and Series E redeemable convertible preferred stock is $0.419463, $0.75503, $0.9061, $1.3592 and $2.1725, respectively, per share, subject to appropriate adjustment in the event of any stock dividend, stock split, combination or other similar recapitalization with respect to the Redeemable Preferred Stock.
	Liquidation Preference
	In the event of any liquidation, voluntary or involuntary, exclusive out-license of all or substantially all of the intellectual property of the Company, dissolution or winding up of the Company or Deemed Liquidation Event (as defined below), the Series A, Series B, Series C, Series D and Series E redeemable convertible preferred stockholders are entitled to receive, in preference to all other stockholders, and to the extent available, an amount equal to the Original Issue Price per share, adjusted for any stock dividends, stock splits or reclassifications, plus all dividends declared but unpaid. In the event that proceeds are not sufficient to permit payment in full to these holders, the proceeds will be ratably distributed among the Series A, Series B, Series C, Series D and Series E holders in proportion to the full preferential amount each such holder is otherwise entitled to receive.
	After payments have been made in full to the holders of the Series A, Series B, Series C, Series D and Series E redeemable convertible preferred stock, then, to the extent available, holders of the common stock and holders of the Series A, Series B, Series C, Series D and Series E redeemable convertible preferred stock will receive the remaining amounts available for distribution ratably in proportion to the number of common shares held by them or issuable to them upon conversion of their redeemable convertible preferred stock into common stock. The distributions are subject to an overall distribution limit of the greater of (i) two times the amount the holders of the Redeemable Preferred Stock are entitled to based on their preference payment and (ii) the amount such holder would have received if such holder had converted shares of the Redeemable Preferred Stock into common stock immediately prior to such dissolution, liquidation, exclusive out-license of all or substantially all of the intellectual property, or winding up of the Company or Deemed Liquidation Event.
	Unless the holders of at least 70% of the then outstanding shares of the Redeemable Preferred Stock, voting together as a single class on an as-converted basis, elect otherwise, a Deemed Liquidation Event shall include a sale of the Company, a sale of the capital stock representing a majority of the voting power or a merger or consolidation of the Company into or with another corporation in which the existing Company holds less than a majority of the voting power of the surviving or resulting corporation, or the sale, lease, transfer, exclusive license or other disposition, in a single transaction or series of related transactions, by the Company of all or substantially all of the assets of the Company.
	Conversion
	Each share of Redeemable Preferred Stock is convertible into common stock at the option of the stockholder at any time after the date of issuance. Each share of the preferred stock will automatically be converted into shares of common stock, at the applicable Series A, Series B, Series C, Series D and Series E redeemable convertible preferred stock conversion ratio then in effect, upon a qualified public offering with net proceeds of not less than $35,000. The conversion ratio of the Series A, Series B, Series C, Series D and Series E redeemable convertible preferred stock, as defined, is determined by dividing the Original Issue Price of each series of preferred stock by the Conversion Price of each series. The Conversion Price of each series shall be $2.63422764 for Series A, $4.7415884 for Series B, $5.690308 for Series C, $8.535776 for Series D and $13.6433 for Series E. The Conversion Price is subject to adjustment as set forth in the Company’s Certificate of Incorporation, as amended and restated, unless at least a majority of the Series A holders, at least 70% of each of Series B or Series C holders, at least 65% of Series D holders and at least a majority of the Series E holders, voting separately as a class with respect to their series, agree that no such adjustment shall be made to their series. As of December 31, 2013, all outstanding shares of Series A, Series B, Series C, Series D and Series E redeemable convertible preferred stock were convertible into common stock on a 6.28-for-1 basis.
	Redemption Rights
	At the written election of at least 70% of the holders of the Series A, Series B, Series C, Series D and Series E redeemable convertible preferred stock, voting together as a single class on an as-converted basis, the shares of Series A, Series B, Series C, Series D and Series E redeemable convertible preferred stock outstanding are redeemable, at any time on or after November 22, 2017, in three equal annual installments commencing sixty days after receipt of the required vote at the Original Issue Price per share of Series A, Series B, Series C, Series D and Series E redeemable convertible preferred stock plus all declared but unpaid dividends thereon.
	The carrying values of the Series A, Series B, Series C, Series D and Series E redeemable convertible preferred stock are being accreted to their redemption values through their respective redemption dates.
	Reissuance
	Shares of any Series A, Series B, Series C, Series D or Series E redeemable convertible preferred stock that are redeemed or converted will be retired or canceled and not reissued by the Company.

Common_Stock

Common Stock	9 Months Ended	12 Months Ended
Common Stock	Sep. 30, 2014	Dec. 31, 2013
Equity [Abstract]
Common Stock	5. Stockholders’ Equity	7. Common Stock
	On June 5, 2014, the Company effected a 1-for-6.28 reverse stock split of its issued and outstanding shares of common stock and a proportional adjustment to the existing conversion ratios for each series of redeemable convertible preferred 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 and adjustment of the redeemable convertible preferred stock conversion ratios.	As of December 31, 2013, the Company’s Certificate of Incorporation, as amended and restated, authorizes the Company to issue 115,000,000 shares of $0.001 par value common stock.
	On June 24, 2014, the Company completed an IPO of its common stock, which resulted in the sale of 6,900,000 shares at a price of $16.00 per share. The Company received net proceeds from the IPO of $102,672 based upon the price of $16.00 per share and after deducting underwriting discounts and commissions paid by the Company. The Company also incurred offering costs of $2,508 related to the IPO.	Each share of common stock entitles the holder to one vote on all matters submitted to a vote of the Company’s stockholders. Common stockholders are entitled to receive dividends, as may be declared by the board of directors, if any, subject to the preferential dividend rights of the Redeemable Preferred Stock. When dividends are declared on shares of common stock, the Company must declare at the same time a dividend payable to the holders of Redeemable Preferred Stock equivalent to the dividend amount they would receive if each preferred share were converted into common stock. The Company may not pay dividends to common stockholders until all dividends accrued or declared but unpaid on the Redeemable Preferred Stock have been paid in full. As of December 31, 2013, no dividends had been declared.
	Upon closing of the IPO, all outstanding shares of the Company’s redeemable convertible preferred stock were converted into 15,077,621 shares of common stock.	During the year ended December 31, 2013, the Company reacquired and retired 6,635 shares of restricted common stock, at cost, that were forfeited by a former employee.
	As of September 30, 2014, the Company’s Certificate of Incorporation, as amended and restated, authorizes the Company to issue 5,000,000 shares of $0.001 par value preferred stock. The rights, preferences, restrictions, qualifications and limitations of such stock are to be determined by the Company’s board of directors.	As of December 31, 2013, the Company had reserved 16,726,699 shares of common stock for the conversion of the outstanding shares of Series A, Series B, Series C, Series D and Series E redeemable convertible preferred stock (see Note 6) and the exercise of stock options and issuance of common stock under the Company’s Amended and Restated 2006 Stock Option Plan (see Note 8).
	As of September 30, 2014 and December 31, 2013, the Company’s Certificate of Incorporation, as amended and restated, authorizes the Company to issue 115,000,000 shares of $0.001 par value common stock.
	During the nine months ended September 30, 2013, the Company reacquired 6,635 shares of restricted common stock, at cost, that were forfeited by a former employee.

StockBased_Awards

Stock-Based Awards	9 Months Ended						12 Months Ended
Stock-Based Awards	Sep. 30, 2014						Dec. 31, 2013
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Stock-Based Awards	6. Stock-Based Awards						8. Stock-Based Awards
	Stock Option Plans						2006 Stock Option Plan
	The Company’s Amended and Restated 2006 Stock Option Plan (the “2006 Plan”) provided for the Company to sell or issue common stock or restricted common stock, or to grant incentive stock options or nonqualified stock options for the purchase of common stock, to employees, members of the board of directors and consultants of the Company. The 2006 Plan is administered by the board of directors, or at the discretion of the board of directors, by a committee of the board. The exercise prices, vesting and other restrictions are determined at the discretion of the board of directors, or a committee of the board of directors if so delegated, except that the exercise price per share of stock options may not be less than 100% of the fair market value of the share of common stock on the date of grant and the term of stock option may not be greater than ten years. The total number of shares of common stock that could be issued under the 2006 Plan was 1,889,150 shares. Upon closing of the Company’s IPO, 168,221 shares reserved and not then subject to outstanding options were transferred to the 2014 Stock Option and Incentive Plan, and no further awards will be made under the 2006 Plan.						The Company’s Amended and Restated 2006 Stock Option Plan (the “2006 Plan”) provides for the Company to sell or issue common stock or restricted common stock, or to grant incentive stock options or nonqualified stock options for the purchase of common stock, to employees, members of the board of directors and consultants of the Company. The 2006 Plan is administered by the board of directors, or at the discretion of the board of directors, by a committee of the board. The exercise prices, vesting and other restrictions are determined at the discretion of the board of directors, or their committee if so delegated, except that the exercise price per share of stock options may not be less than 100% of the fair market value of the share of common stock on the date of grant and the term of stock option may not be greater than ten years.
	On June 5, 2014, the Company’s stockholders approved the 2014 Stock Option and Incentive Plan (the “2014 Stock Option Plan”), which became effective upon the completion of the IPO of the Company’s shares of common stock in June 2014. The 2014 Stock Option Plan provides for the grant of stock options, stock appreciation rights, restricted stock, restricted stock units, unrestricted stock, performance-share awards and cash-based awards. The number of shares initially reserved for issuance under the 2014 Stock Option Plan is 2,168,221 shares of common stock and may be increased by the number of shares under the 2006 Plan that are not needed to fulfill the Company’s obligations for awards issued under the 2006 Plan as a result of forfeiture, expiration, cancellation, termination or net issuances of awards thereunder. The number of shares of common stock that may be issued under the plan is also subject to increase on the first day of each fiscal year by the lesser of (i) 4% of the Company’s outstanding shares of common stock as of that date, or (ii) an amount determined by the board of directors.						Stock options granted under the 2006 Plan generally vest over four years and expire after ten years, although options have been granted with vesting terms less than four years.
	The Company generally grants stock-based awards with service conditions only (“service-based” awards).						The total number of shares of common stock that may be issued under the 2006 Plan was 1,889,150 shares as of December 31, 2013, of which 371,244 shares remained available for future grant at December 31, 2013.
	As required by the 2006 Plan and 2014 Stock Option Plan, the exercise price for stock options granted is not to be less than the fair value of common shares as of the date of grant. Prior to the IPO, the value of common stock was determined by the board of directors by taking into consideration its most recently available valuation of common shares performed by management and the board of directors as well as additional factors which might have changed since the date of the most recent contemporaneous valuation through the date of grant.						The Company generally grants stock-based awards with service conditions only (“service-based” awards).
	During the nine months ended September 30, 2014, the Company granted stock options for the purchase of 529,565 shares of common stock, of which options for the purchase of 527,973 shares were granted to employees and options for the purchase of 1,592 shares were granted to a consultant.						As required by the 2006 Plan, the exercise price for stock options granted is not to be less than the fair value of common shares as determined by the Company as of the date of grant. The Company values its common stock by taking into consideration its most recently available valuation of common shares performed by management and the board of directors as well as additional factors which may have changed since the date of the most recent contemporaneous valuation through the date of grant.
	2014 Employee Stock Purchase Plan
	On June 5, 2014, the Company’s stockholders approved the 2014 Employee Stock Purchase Plan. A total of 265,000 shares of common stock were reserved for issuance under this plan. The 2014 Employee Stock Purchase Plan became effective upon the completion of the IPO of the Company’s shares of common stock. The first offering period commenced on September 1, 2014. The per share purchase price for offerings is equal to the lesser of 85% of the closing market price of the Company’s common stock on the first day or last day of the offering period. As of September 30, 2014, there are 265,000 shares of common stock available for issuance to participating employees under the plan.						Stock Option Valuation
	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. The Company historically has been a private company and lacks company-specific historical and implied volatility information. Therefore, it estimates its expected stock volatility based on the historical volatility of a publicly traded set of peer companies and expects to continue to do so until such time as it has adequate historical data regarding the volatility of its own traded stock price. The expected term of the Company’s stock options has been determined utilizing the “simplified” method for awards that qualify as “plain-vanilla” options. The expected term of stock options granted to nonemployees 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 assumptions that the Company used to determine the fair value of the stock options granted to employees and directors are as follows, presented on a weighted average basis (the Company did not grant any stock options to employees or directors during the year ended December 31, 2012):
	The fair value of each stock option grant is estimated on the date of grant using the Black-Scholes option-pricing model. The Company historically has been a private company and lacks company-specific historical and implied volatility information. Therefore, it estimates its expected stock volatility based on the historical volatility of a publicly traded set of peer companies and expects to continue to do so until such time as it has adequate historical data regarding the volatility of its own traded stock price. The expected term of the Company’s stock options has been determined utilizing the “simplified” method for awards that qualify as “plain-vanilla” options. The expected term of stock options granted to nonemployees 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.
	As of September 30, 2014, there were outstanding unvested service-based stock options held by nonemployees for the purchase of 17,513 shares of common stock. Additionally as of September 30, 2014, there were outstanding unvested performance-based stock options held by nonemployees for the purchase of 796 shares of common stock.
									Year Ended December 31,
	Stock-based Compensation								2011				2013
	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:						Risk-free interest rate			1.41	%			1.12	%
							Expected term (in years)			6.25				6.25
							Expected volatility			78	%			85	%
		Nine Months Ended					Expected dividend yield			0	%			0	%
		September 30,					The following table summarizes the Company’s stock option activity since January 1, 2011:
		2014		2013
	Research and development	$	259	$	109
	General and administrative		651		143				Shares Issuable				Weighted				Weighted		Aggregate
									Under Options				Average				Average		Intrinsic
		$	910	$	252								Exercise				Remaining		Value
													Price				Contractual
	As of September 30, 2014, the Company had an aggregate of $6,224 of unrecognized stock-based compensation cost, which is expected to be recognized over a weighted average period of 3.4 years.																Term
																	(In years)
							Outstanding as of January 1, 2011			440,301			$	0.75				8.5	$	216
							Granted			475,793				1.57
							Exercised			—				—
							Forfeited			—				—

							Outstanding as of December 31, 2011			916,094			$	1.19				8.7	$	354
							Granted			7,961				1.57
							Exercised			(16,069	)			0.88
							Forfeited			(316,559	)			1.57

							Outstanding as of December 31, 2012			591,427			$	1				7.1	$	342
							Granted			718,903				2.64
							Exercised			—
							Forfeited			—

							Outstanding as of December 31, 2013			1,310,330			$	1.88				7.8	$	10,185

							Options vested and expected to vest as of December 31, 2013			1,310,330			$	1.88				7.8	$	10,185

							Options exercisable as of December 31, 2013			657,317			$	1.26				6.6	$	5,543


							The aggregate intrinsic value of stock options is calculated as the difference between the exercise price of the stock options and the fair value of the Company’s common stock for those stock options that had exercise prices lower than the fair value of the Company’s common stock. The aggregate intrinsic value of stock options exercised was $12 during the year ended December 31, 2012. No stock options were exercised during the years ended December 31, 2011 or 2013.
							The Company received cash proceeds from the exercise of stock options of $13 during the year ended December 31, 2012.
							The weighted average grant-date fair value of stock options granted to employees and directors during the years ended December 31, 2011 and 2013 was $1.07 and $1.83 per share, respectively. The Company did not grant stock options to employees or directors in 2012. The grant of stock options in 2012 was to a consultant.
							As of December 31, 2013, there were outstanding unvested service-based stock options held by nonemployees for the purchase of 17,513 shares of common stock. Additionally as of December 31, 2013, there were outstanding unvested performance-based stock options held by nonemployees for the purchase of 796 shares of common stock.
							Restricted Common Stock
							The 2006 Plan provides for the award of restricted stock. The Company has granted restricted common stock 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 since January 1, 2011:


									Shares				Weighted
													Average Grant-
													Date Fair Value
							Unvested restricted common stock as of January 1, 2011			38,481			$	0.82
							Issued			—				—
							Vested			(13,933	)			0.75
						Forfeited			—				—

						Unvested restricted common stock as of December 31, 2011			24,548			$	0.82
						Issued			—				—
						Vested			(13,933	)			0.75
						Forfeited			—				—

						Unvested restricted common stock as of December 31, 2012			10,615			$	0.82
						Issued			—				—
						Vested			(3,980	)			0.75
						Forfeited			(6,635	)			0.82

						Unvested restricted common stock as of December 31, 2013			—				—

						The aggregate intrinsic value of restricted stock awards is calculated as the difference between the grant-date fair value of the restricted stock awards and the fair value of the Company’s common stock. The aggregate intrinsic value of restricted stock awards that vested during each of the years ended December 31, 2011, 2012 and 2013 was $22, $22 and $38, respectively. As of December 31, 2013, there were no unvested restricted stock awards subject to repurchase.

						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,
								2011				2012				2013
						Research and development		$	30			$	68			$	176
						General and administrative			50				53				219

								$	80			$	121			$	395

						As of December 31, 2013, the Company had an aggregate of $1,334 of unrecognized stock-based compensation cost, which is expected to be recognized over a weighted average period of 3.6 years.

Net_Loss_Per_Share

Net Loss Per Share	12 Months Ended
Net Loss Per Share	Dec. 31, 2013
Earnings Per Share [Abstract]
Net Loss Per Share	9. Net Loss Per Share

	Net Loss Per Share

	Basic and diluted net loss per share attributable to common stockholders was calculated as follows for the years ended December 31, 2011, 2012 and 2013:



		Year Ended December 31,
		2011			2012			2013
	Numerator:
	Net loss	$	(13,157	)	$	(13,880	)	$	(14,027	)
	Accretion of redeemable convertible preferred stock to redemption value		(53	)		(67	)		(213	)

	Net loss attributable to common stockholders	$	(13,210	)	$	(13,947	)	$	(14,240	)

	Denominator:
	Weighted average common shares outstanding, basic and diluted		688,946			709,678			729,001

	Net loss per share attributable to common stockholders, basic and diluted	$	(19.17	)	$	(19.65	)	$	(19.53	)


	The Company excluded the following common stock equivalents, outstanding as of December 31, 2011, 2012 and 2013, from the computation of diluted net loss per share attributable to common stockholders for the years ended December 31, 2011, 2012 and 2013 because they had an anti-dilutive impact due to the net loss attributable to common stockholders incurred for the periods.



		December 31,
		2011			2012			2013
	Stock options to purchase common stock		916,094			591,427			1,310,330
	Unvested restricted common stock		24,548			10,615			—

			940,642			602,042			1,310,330

Commitments_and_Contingencies

Commitments and Contingencies	9 Months Ended			12 Months Ended
Commitments and Contingencies	Sep. 30, 2014			Dec. 31, 2013
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	7. Commitments and Contingencies			10. Commitments and Contingencies
	Leases			Leases
	On May 15, 2014, the Company entered into a new lease for office space in Boston, Massachusetts, effective as of July 28, 2014, with a term expiring July 31, 2017 and an option to extend the lease for three additional years.			The Company leases its office space under an operating lease agreement that initially expired on July 31, 2013, but was amended in 2013 to extend the lease through January 31, 2014. The lease, as amended, allows for up to two six-month extension periods. In December 2013, the Company extended the lease through July 31, 2014, cancellable with 30 days’ notice.
	Future minimum lease payments for its operating leases as of September 30, 2014, are as follows:			Future minimum lease payments for its operating lease as of December 31, 2013 were as follows:


	Year Ending December 31,			Year Ending December 31,
	Remainder of 2014	$	57	2014	$	64
	2015		229
	2016		235	Total	$	64
	2017		139
				The Company also leased laboratory space in prior years; however, these leases terminated prior to 2011 and, as of December 31, 2013, there are no future commitments for laboratory space. During the years ended December 31, 2011, 2012 and 2013, the Company recognized $102, $129 and $105, respectively, of rental expense related to office space.
	Total	$	660	Intellectual Property Licenses
				The Company has acquired exclusive rights to develop patented compounds and related know-how for beloranib under two licensing agreements with two third parties in the course of its research and development activities. The licensing rights obligate the Company to make payments to the licensors for license fees, milestones, license maintenance fees and royalties. The Company is also responsible for patent prosecution costs. Related to these license agreements, the Company made payments and recorded research and development expenses in its consolidated statements of operations as follows:
	During the nine months ended September 30, 2014 and 2013, the Company recognized $104 and $87, respectively, of rental expense related to office space.
	Intellectual Property Licenses
	The Company has acquired exclusive rights to develop patented compounds and related know-how for beloranib under two licensing agreements with two third parties in the course of its research and development activities. The licensing rights obligate the Company to make payments to the licensors for license fees, milestones, license maintenance fees and royalties. The Company is also responsible for patent prosecution costs.				Year Ended December 31,
	As of September 30, 2014, the Company recorded a liability of $6,700 relating to milestones achieved in September 2014 upon the initiation of a first Phase 3 clinical trial. As of September 30, 2014, the Company is obligated to make additional milestone payments of up to $12,250 upon reaching certain pre-commercialization milestones, such as clinical trials and government approvals, and up to $12,500 upon reaching certain product commercialization milestones. Under one of the license agreements, the Company is also obligated to pay up to $1,250 with respect to each subsequent licensed product, if any, that is a new chemical entity. In addition, the Company will owe single-digit royalties on sales of commercial products developed using these licensed technologies, if any. The Company is also obligated to pay to the licensors a percentage of fees received if and when the Company sublicenses the technology. As of September 30, 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.				2011		2012		2013
	Indemnification Agreements			Licensing, milestone and license maintenance fees	$	1,055	$	150	$	—
	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. In addition, the Company has entered into indemnification agreements with members of its board of directors that will require the Company, among other things, to indemnify them against certain liabilities that may arise by reason of their status or service as directors or officers. The maximum potential amount of future payments the Company could be required to make under these indemnification agreements is, in many cases, unlimited. To date, the Company has not incurred any material costs as a result of such indemnifications. 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 September 30, 2014.
				The Company is obligated to make additional milestone payments of up to $18,950 upon reaching certain pre-commercialization milestones, such as clinical trials and government approvals, and up to $12,500 upon reaching certain product commercialization milestones. Under one of the license agreements, the Company is also obligated to pay up to $1,250 with respect to each subsequent licensed product, if any, that is a new chemical entity. In addition, the Company will owe single-digit royalties on sales of commercial products developed using these licensed technologies, if any. The Company is also obligated to pay to the licensors a percentage of fees received if and when the Company sublicenses the technology. As of December 31, 2013, 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.
				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. In addition, the Company has entered into indemnification agreements with members of its board of directors that will require the Company, among other things, to indemnify them against certain liabilities that may arise by reason of their status or service as directors or officers. The maximum potential amount of future payments the Company could be required to make under these indemnification agreements is, in many cases, unlimited. To date, the Company has not incurred any material costs as a result of such indemnifications. 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, 2012 or 2013.

Income_Taxes

Income Taxes	12 Months Ended
Income Taxes	Dec. 31, 2013
Income Tax Disclosure [Abstract]
Income Taxes	11. Income Taxes
	During the years ended December 31, 2011, 2012 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,
		2011			2012			2013
	Federal statutory income tax rate		(34.0	%)		(34.0	%)		(34.0	%)
	Federal and state research and development tax credit		(6.4	)		(1.2	)		(9.0	)
	Orphan drug tax credit		—			—			(3.1	)
	State taxes, net of federal benefit		(5.4	)		(5.0	)		(4.0	)
	Meals and entertainment		0.1			—			—
	Stock-based compensation expense		0.2			0.2			0.6
	Nondeductible Australia research and development expenses		—			1.8			4.1
	Change in deferred tax asset valuation allowance		45.5			38.2			45.4

	Effective income tax rate		0	%		0	%		0	%


	Net deferred tax assets as of December 31, 2012 and 2013 consisted of the following:


		December 31,
		2012			2013
	Accrued expenses	$	46		$	18
	Other temporary differences		1			2

	Total current deferred tax assets		47			20

	Noncurrent deferred tax assets:
	Capitalized research and development expenses		16,676			19,856
	Net operating loss carryforwards		3,209			4,021
	Tax credit carryforwards		3,656			5,579
	Capitalized legal expenses		385			790
	Stock-based compensation		33			91

	Total noncurrent deferred tax assets		23,959			30,337

	Total gross deferred tax assets		24,006			30,357
	Valuation allowance		(24,006	)		(30,357	)

	Net deferred tax assets	$	—		$	—

	Changes in the valuation allowance for deferred tax assets during the years ended December 31, 2011, 2012 and 2013 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,
		2011			2012			2013
	Valuation allowance as of beginning of year	$	12,748		$	18,744		$	24,006
	Decreases recorded as benefit to income tax provision		—			—			—
	Increases recorded to income tax provision		5,996			5,262			6,351

	Valuation allowance as of end of year	$	18,744		$	24,006		$	30,357

	As of December 31, 2013, the Company had net operating loss carryforwards for federal and state income tax purposes of $10,548 and $8,226, respectively, which begin to expire in 2026 and 2014, respectively. The Company also had an additional $16 of federal and state net operating losses not reflected above that were attributable to stock option exercises, which will be recorded as an increase in additional paid-in capital once they are realized in accordance with accounting for stock-based compensation awards. As of December 31, 2013, the Company also had available research and development tax credit carryforwards for federal and state income tax purposes of $4,706 and $1,322, respectively, which begin to expire in 2026 and 2021, respectively. Utilization of the net operating loss carryforwards and research and development tax credit carryforwards may be subject to a substantial annual limitation under Section 382 of the Internal Revenue Code of 1986 due to ownership changes that 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. In general, an ownership change, as defined by Section 382, results from transactions increasing the ownership of certain shareholders or public groups in the stock of a corporation by more than 50% over a three-year period. The Company has not conducted a 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, at any time since inception, utilization of the net operating loss carryforwards or research and development tax credit carryforwards would be subject to an annual limitation under Section 382, 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, 2012 and 2013, the Company’s gross deferred tax asset balance of $24,006 and $30,357, respectively, was comprised principally of net operating loss carryforwards, capitalized research and development expenses and research and development tax credit carryforwards. During the years ended December 31, 2011, 2012 and 2013, gross deferred tax assets increased due to additional net operating loss carryforwards, research and development tax credits generated and additional research and development expenses capitalized for tax purposes.
	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 or generation of any revenue from product sales 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, 2012 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, 2012 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 2010 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.

Retirement_Plan

Retirement Plan	9 Months Ended	12 Months Ended
Retirement Plan	Sep. 30, 2014	Dec. 31, 2013
Compensation and Retirement Disclosure [Abstract]
Retirement Plan	8. Retirement Plan	12. Retirement Plan
Retirement Plan	The Company has a Savings Incentive Match Plan for employees. Under the terms of the plan, the Company contributes 2% of an employee’s annual base salary, up to a maximum of the annual Internal Revenue Service compensation limits, for all full-time employees. During the nine months ended September 30, 2014 and 2013, the Company recognized $43 and $20, respectively, of expense related to its contributions to the plan.	In 2009, the Company established a Savings Incentive Match Plan for employees. Under the terms of the plan, the Company contributes 2% of an employee’s annual base salary, up to a maximum of the annual Internal Revenue Service compensation limits, for all full-time employees. During the years ended December 31, 2011, 2012 and 2013, the Company recognized $15, $16 and $26, respectively, of expense related to its contributions to this plan.

Australia_Research_and_Develop

Australia Research and Development Tax Incentive	9 Months Ended	12 Months Ended
Australia Research and Development Tax Incentive	Sep. 30, 2014	Dec. 31, 2013
Research and Development [Abstract]
Australia Research and Development Tax Incentive	9. Australia Research and Development Tax Incentive	13. Australia Research and Development Tax Incentive
Australia Research and Development Tax Incentive	The Company’s wholly owned subsidiary, Zafgen Australia Pty Limited, which conducts core research and development activities on behalf of the Company, is eligible to receive a 45% refundable tax incentive for qualified research and development activities. For the nine months ended September 30, 2014 and 2013, $368 and $1,230, respectively, was recorded as a reduction to research and development expenses in the consolidated statements of operations. These amounts represented 45% of the Company’s qualified research and development spending in Australia. The refund is denominated in Australian dollars and, therefore, the related receivable is re-measured into U.S. dollars as of each reporting date. For the nine months ended September 30, 2014 and 2013, the Company recorded in its consolidated statements of operations unrealized foreign currency exchange (gains) losses of $31 and $169, respectively, related to this tax incentive receivable. As of September 30, 2014 and December 31, 2013, the Company’s tax incentive receivable from the Australian government was $1,218 and $1,617, respectively.	The Australian government has established a research and development tax incentive to encourage industry investment in research and development, which is available to companies incorporated under an Australian law that have core research and development activities. The Company established Zafgen Australia Pty Limited, a wholly owned subsidiary, in October 2012 to carry out certain research and development activities. As this subsidiary meets the eligibility requirements of the Australian tax law, it is eligible to receive a 45% refundable tax incentive for qualified research and development activities. For the years ended December 31, 2012 and 2013, $630 and $1,237, respectively, was recorded as a reduction to research and development expenses in the consolidated statements of operations, representing 45% of the Company’s qualified research and development spending in Australia. The refund is denominated in Australian dollars and, therefore, the receivable is re-measured into U.S. dollars as of each reporting date. For the year ended December 31, 2013, the Company recorded in its consolidated statements of operations unrealized foreign currency exchange (gains) losses of $250 related to this tax incentive receivable. The Company did not have any foreign exchange gains or losses related to this receivable for periods prior to 2013. As of December 31, 2012 and 2013, the Company’s tax incentive receivable from the Australian government was $630 and $1,617.

Related_Party_Transactions

Related Party Transactions	12 Months Ended
Related Party Transactions	Dec. 31, 2013
Related Party Transactions [Abstract]
Related Party Transactions	14. Related Party Transactions
Related Party Transactions	In October 2011, the Company entered into an agreement with a member of the board of directors under which the board member would also serve as a business development consultant. Under the terms of the agreement, the annual consulting fee was $80. Additionally, a success fee of $500 would be earned upon a change in control of the Company. During the years ended December 31, 2011 and 2012, the Company paid the board member $18 and $80, respectively, for consulting services. This agreement was terminated in 2012.

Subsequent_Events

Subsequent Events	12 Months Ended
Subsequent Events	Dec. 31, 2013
Subsequent Events [Abstract]
Subsequent Events	15. Subsequent Events

	Issuance of Series E Redeemable Convertible Prefered Stock

	In February 2014, the Company issued 204,101 shares of Series E redeemable convertible preferred stock at an issuance price equal to $2.1725 per share and received gross proceeds of $443. In connection with this financing, the Company paid total issuance costs of $1.

	Reverse Stock Split

	On June 5, 2014, the Company effected a 1-for-6.28 reverse stock split of its issued and outstanding shares of common stock and a proportional adjustment to the existing conversion ratios for each series of Redeemable Preferred Stock (see Note 6). 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 and adjustment of the preferred stock conversion ratios.

Summary_of_Significant_Account1

Summary of Significant Accounting Policies (Policies)

9 Months Ended

12 Months Ended

Sep. 30, 2014

Dec. 31, 2013

Accounting Policies [Abstract]

Use of Estimates

The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, the disclosure of contingent assets and liabilities at the date of the consolidated financial statements, and the reported amounts of expenses during the reporting periods. Significant estimates and assumptions reflected in these consolidated financial statements include, but are not limited to, the accrual of research and development expenses and the valuation of common stock and 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

Concentration of Credit Risk and of Significant Suppliers

Fair Value Measurements

•

Level 1—Quoted prices in active markets for identical assets or liabilities.

•

Level 1—Quoted prices in active markets for identical assets or 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 recorded $743 of deferred offering costs, included in other assets in the accompanying consolidated balance sheet, in contemplation of a probable 2014 equity financing. Should the equity financing no longer be considered probable of being consummated, the deferred offering costs would be expensed immediately as a charge to operating expenses in the consolidated statement of operations. The Company did not record any deferred offering costs as of December 31, 2012.

Property and Equipment

Impairment of Long-Lived Assets

Research and Development Costs

Research and development costs are expensed as incurred. Included in research and development expenses are wages, stock-based compensation and benefits of employees, third-party license fees and other operational costs related to the Company’s research and development activities, including facility-related expenses and external costs of outside vendors engaged to conduct both pre-clinical studies and clinical trials. The Company records research and development expenses net of any research and development tax incentives the Company is entitled to receive from government authorities.

Research Contract Costs and Accruals

Patent Costs

Accounting for Stock-Based Compensation

Income Taxes

Segment Data

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 nine months ended September 30, 2014 and 2013, there was no difference between net loss and comprehensive loss.

Net Income (Loss) Per Share

The Company reported a net loss attributable to common stockholders for the nine months ended September 30, 2014 and 2013.

As of September 30,

2014

2013

Options to purchase common stock

1,839,895

1,283,264

Redeemable convertible preferred stock

—

78,372,931

Total options and redeemable convertible preferred stock exercisable or convertible into common stock

1,839,895

79,656,195

Recently Issued and Adopted Accounting Pronouncements

Unaudited Interim Financial Information

The consolidated balance sheet at December 31, 2013 was derived from audited financial statements, but does not include all disclosures required by GAAP. The accompanying unaudited consolidated financial statements as of September 30, 2014, and for the nine months ended September 30, 2014 and 2013, have been prepared by the Company, pursuant to the rules and regulations of the SEC for interim financial statements. Certain information and footnote disclosures normally included in financial statements prepared in accordance with GAAP have been condensed or omitted pursuant to such rules and regulations. However, the Company believes that the disclosures are adequate to make the information presented not misleading. These consolidated financial statements should be read in conjunction with the Company’s audited consolidated financial statements and the notes thereto for the year ended December 31, 2013. In the opinion of management, all adjustments, consisting only of normal recurring adjustments necessary for a fair statement of the Company’s consolidated financial position as of September 30, 2014 and consolidated results of operations and consolidated cash flows for the nine months ended September 30, 2014 and 2013 have been made. The results for the nine months ended September 30, 2014 are not necessarily indicative of the results that may be expected for the year ending December 31, 2014, any other interim periods, or any future year or period.

Property_and_Equipment_net_Tab

Property and Equipment, net (Tables)	12 Months Ended
Property and Equipment, net (Tables)	Dec. 31, 2013
Property, Plant and Equipment [Abstract]
Schedule of Property and Equipment, Net	Property and equipment, net consisted of the following as of December 31, 2012 and 2013:


		December 31,
		2012			2013
	Office equipment	$	10		$	27
	Furniture and fixtures		44			44

			54			71
	Less: Accumulated depreciation		(22	)		(34	)

		$	32		$	37

	Depreciation expense was $4, $11 and $12 for the years ended December 31, 2011, 2012 and 2013, respectively.

Accrued_Expenses_Tables

Accrued Expenses (Tables)	9 Months Ended					12 Months Ended
Accrued Expenses (Tables)	Sep. 30, 2014					Dec. 31, 2013
Payables and Accruals [Abstract]
Schedule of Accrued Expenses	Accrued expenses consisted of the following:					Accrued expenses consisted of the following as of December 31, 2012 and 2013:


		September 30,		December 31,			December 31,
		2014		2013			2012		2013
	Accrued licensing milestone fees	$	6,700	$	—	Accrued payroll and related expenses	$	74	$	49
	Accrued research and development expenses		1,759		616	Accrued research and development expenses		1,558		616
	Accrued payroll and related expenses		741		49	Accrued professional fees		62		196
	Accrued professional fees		542		196	Accrued other		5		39
	Accrued interest		51		—
	Accrued other		92		39		$	1,699	$	900

		$	9,885	$	900

Redeemable_Convertible_Preferr1

Redeemable Convertible Preferred Stock (Tables)	12 Months Ended
Redeemable Convertible Preferred Stock (Tables)	Dec. 31, 2013
Equity [Abstract]
Schedule of Redeemable Preferred Stock	Redeemable Preferred Stock consisted of the following as of December 31, 2012:


		Preferred		Preferred		Liquidation		Carrying		Common
		Shares		Shares		Preference		Value		Stock Issuable
		Authorized		Issued and						Upon
				Outstanding						Conversion
	Series A redeemable convertible preferred stock		5,363,239		5,363,239	$	2,250	$	2,222		854,018
	Series B redeemable convertible preferred stock		40,266,246		40,266,246		30,402		30,335		6,411,822
	Series C redeemable convertible preferred stock		16,732,284		16,732,284		15,161		15,137		2,664,376
	Series D redeemable convertible preferred stock		16,011,162		11,629,248		15,816		15,091		1,851,791

			78,372,931		73,991,017	$	63,629	$	62,785		11,782,007

	Redeemable Preferred Stock consisted of the following as of December 31, 2013:


		Preferred		Preferred		Liquidation		Carrying		Common
		Shares		Shares		Preference		Value		Stock Issuable
		Authorized		Issued and						Upon
				Outstanding						Conversion
	Series A redeemable convertible preferred stock		5,363,239		5,363,239	$	2,250	$	2,229		854,018
	Series B redeemable convertible preferred stock		40,266,246		40,266,246		30,402		30,351		6,411,822
	Series C redeemable convertible preferred stock		16,732,284		16,732,284		15,161		15,144		2,664,376
	Series D redeemable convertible preferred stock		16,011,162		16,011,162		21,775		21,226		2,549,548
	Series E redeemable convertible preferred stock		20,919,679		16,110,473		35,000		34,847		2,565,361

			99,292,610		94,483,404	$	104,588	$	103,797		15,045,125

StockBased_Awards_Tables

Stock-Based Awards (Tables)	9 Months Ended					12 Months Ended
Stock-Based Awards (Tables)	Sep. 30, 2014					Dec. 31, 2013
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Assumptions used to Determine Fair Value of Stock Options Granted						The assumptions that the Company used to determine the fair value of the stock options granted to employees and directors are as follows, presented on a weighted average basis (the Company did not grant any stock options to employees or directors during the year ended December 31, 2012):


							Year Ended December 31,
							2011			2013
						Risk-free interest rate		1.41	%		1.12	%
						Expected term (in years)		6.25			6.25
						Expected volatility		78	%		85	%
						Expected dividend yield		0	%		0	%
Summary of Stock Option Activity						The following table summarizes the Company’s stock option activity since January 1, 2011:


							Shares Issuable			Weighted			Weighted		Aggregate
							Under Options			Average			Average		Intrinsic
										Exercise			Remaining		Value
										Price			Contractual
													Term
													(In years)
						Outstanding as of January 1, 2011		440,301		$	0.75			8.5	$	216
						Granted		475,793			1.57
						Exercised		—			—
						Forfeited		—			—

						Outstanding as of December 31, 2011		916,094		$	1.19			8.7	$	354
						Granted		7,961			1.57
						Exercised		(16,069	)		0.88
						Forfeited		(316,559	)		1.57

						Outstanding as of December 31, 2012		591,427		$	1			7.1	$	342
						Granted		718,903			2.64
						Exercised		—
						Forfeited		—

						Outstanding as of December 31, 2013		1,310,330		$	1.88			7.8	$	10,185

						Options vested and expected to vest as of December 31, 2013		1,310,330		$	1.88			7.8	$	10,185

						Options exercisable as of December 31, 2013		657,317		$	1.26			6.6	$	5,543

Summary of Restricted Stock Activity						The table below summarizes the Company’s restricted stock activity since January 1, 2011:


							Shares			Weighted
										Average Grant-
										Date Fair Value
						Unvested restricted common stock as of January 1, 2011		38,481		$	0.82
						Issued		—			—
						Vested		(13,933	)		0.75
						Forfeited		—			—

						Unvested restricted common stock as of December 31, 2011		24,548		$	0.82
						Issued		—			—
						Vested		(13,933	)		0.75
						Forfeited		—			—

						Unvested restricted common stock as of December 31, 2012		10,615		$	0.82
						Issued		—			—
						Vested		(3,980	)		0.75
						Forfeited		(6,635	)		0.82

						Unvested restricted common stock as of December 31, 2013		—			—

Summary 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:					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:


		Nine Months Ended					Year Ended December 31,
		September 30,					2011			2012			2013
		2014		2013		Research and development	$	30		$	68		$	176
	Research and development	$	259	$	109	General and administrative		50			53			219
	General and administrative		651		143
							$	80		$	121		$	395
		$	910	$	252

Net_Loss_Per_Share_Tables

Net Loss Per Share (Tables)	9 Months Ended					12 Months Ended
Net Loss Per Share (Tables)	Sep. 30, 2014					Dec. 31, 2013
Earnings Per Share [Abstract]
Computation of Basic and Diluted Earnings Per Share						Basic and diluted net loss per share attributable to common stockholders was calculated as follows for the years ended December 31, 2011, 2012 and 2013:


							Year Ended December 31,
							2011			2012			2013
						Numerator:
						Net loss	$	(13,157	)	$	(13,880	)	$	(14,027	)
						Accretion of redeemable convertible preferred stock to redemption value		(53	)		(67	)		(213	)

						Net loss attributable to common stockholders	$	(13,210	)	$	(13,947	)	$	(14,240	)

						Denominator:
						Weighted average common shares outstanding, basic and diluted		688,946			709,678			729,001

						Net loss per share attributable to common stockholders, basic and diluted	$	(19.17	)	$	(19.65	)	$	(19.53	)

Summary of Common Stock Equivalents Outstanding	The following common stock equivalents, outstanding as of September 30, 2014 and 2013, were excluded from the computation of diluted net loss per share for the nine months ended September 30, 2014 and 2013 because they had an anti-dilutive impact:					The Company excluded the following common stock equivalents, outstanding as of December 31, 2011, 2012 and 2013, from the computation of diluted net loss per share attributable to common stockholders for the years ended December 31, 2011, 2012 and 2013 because they had an anti-dilutive impact due to the net loss attributable to common stockholders incurred for the periods.


		As of September 30,					December 31,
		2014		2013			2011			2012			2013
						Stock options to purchase common stock		916,094			591,427			1,310,330
	Options to purchase common stock		1,839,895		1,283,264	Unvested restricted common stock		24,548			10,615			—
	Redeemable convertible preferred stock		—		78,372,931
								940,642			602,042			1,310,330
	Total options and redeemable convertible preferred stock exercisable or convertible into common stock		1,839,895		79,656,195

Commitments_and_Contingencies_

Commitments and Contingencies (Tables)	9 Months Ended			12 Months Ended
Commitments and Contingencies (Tables)	Sep. 30, 2014			Dec. 31, 2013
Commitments and Contingencies Disclosure [Abstract]
Schedule of Future Minimum Lease Payments for Operating Leases	Future minimum lease payments for its operating leases as of September 30, 2014, are as follows:			Future minimum lease payments for its operating lease as of December 31, 2013 were as follows:


	Year Ending December 31,			Year Ending December 31,
	Remainder of 2014	$	57	2014	$	64
	2015		229
	2016		235	Total	$	64
	2017		139

	Total	$	660

Research and Development Expenses Related to License Agreements				Related to these license agreements, the Company made payments and recorded research and development expenses in its consolidated statements of operations as follows:


					Year Ended December 31,
					2011		2012		2013
				Licensing, milestone and license maintenance fees	$	1,055	$	150	$	—

Income_Taxes_Tables

Income Taxes (Tables)	12 Months Ended
Income Taxes (Tables)	Dec. 31, 2013
Income Tax Disclosure [Abstract]
Reconciliation of 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,
		2011			2012			2013
	Federal statutory income tax rate		(34.0	%)		(34.0	%)		(34.0	%)
	Federal and state research and development tax credit		(6.4	)		(1.2	)		(9.0	)
	Orphan drug tax credit		—			—			(3.1	)
	State taxes, net of federal benefit		(5.4	)		(5.0	)		(4.0	)
	Meals and entertainment		0.1			—			—
	Stock-based compensation expense		0.2			0.2			0.6
	Nondeductible Australia research and development expenses		—			1.8			4.1
	Change in deferred tax asset valuation allowance		45.5			38.2			45.4

	Effective income tax rate		0	%		0	%		0	%

Schedule of Net Deferred tax Assets	Net deferred tax assets as of December 31, 2012 and 2013 consisted of the following:


		December 31,
		2012			2013
	Accrued expenses	$	46		$	18
	Other temporary differences		1			2

	Total current deferred tax assets		47			20

	Noncurrent deferred tax assets:
	Capitalized research and development expenses		16,676			19,856
	Net operating loss carryforwards		3,209			4,021
	Tax credit carryforwards		3,656			5,579
	Capitalized legal expenses		385			790
	Stock-based compensation		33			91

	Total noncurrent deferred tax assets		23,959			30,337

	Total gross deferred tax assets		24,006			30,357
	Valuation allowance		(24,006	)		(30,357	)

	Net deferred tax assets	$	—		$	—

Summary of Changes in the Valuation Allowance for Deferred Tax Assets	Changes in the valuation allowance for deferred tax assets during the years ended December 31, 2011, 2012 and 2013 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,
		2011			2012			2013
	Valuation allowance as of beginning of year	$	12,748		$	18,744		$	24,006
	Decreases recorded as benefit to income tax provision		—			—			—
	Increases recorded to income tax provision		5,996			5,262			6,351

	Valuation allowance as of end of year	$	18,744		$	24,006		$	30,357

Convertible_Promissory_Notes_T

Convertible Promissory Notes (Tables)	9 Months Ended
Convertible Promissory Notes (Tables)	Sep. 30, 2014
Debt Disclosure [Abstract]
Schedule of Estimated Future Principal Payments Due under Term Loan	Estimated future principal payments due under the Term Loan A are as follows:


	Years Ending December 31,
	Remainder of 2014	$	—
	2015		1,381
	2016		2,936
	2017		3,183

	Total	$	7,500

Nature_of_the_Business_and_Bas1

Nature of the Business and Basis of Presentation - Additional Information (Detail) (USD $)	9 Months Ended	12 Months Ended	0 Months Ended
In Thousands, except Share data, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013	Jun. 24, 2014	Dec. 31, 2012
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]
Entity incorporation date	22-Nov-05	22-Nov-05
Accumulated deficit	($94,454)	($68,907)		($54,880)
Net proceeds from initial public offering	102,672
Maximum [Member]
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]
Net proceeds from initial public offering		35,000
Common Stock [Member] \| IPO [Member]
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]
Net proceeds from initial public offering			102,672
Initial public offering, common stock issued, shares			6,900,000
Initial public offering, common stock issued per share			$16
Offering costs incurred			$2,508

Summary_of_Significant_Account2

Summary of Significant Accounting Policies - Additional Information (Detail) (USD $)	9 Months Ended	12 Months Ended
	Sep. 30, 2014	Dec. 31, 2013	Dec. 31, 2012
Summary Of Significant Accounting Policies [Line Items]
Short-term investments maturity, description	Ninety days or less	Ninety days or less
Deferred offering costs	$0	$743,000	$0
Estimated useful life	5 years	5 years
Impairment losses on long-lived assets	0	0
Percentage of likelihood to be realized upon ultimate settlement, description	50.00%	50.00%
Quoted prices in active markets, Level 1 [Member]
Summary Of Significant Accounting Policies [Line Items]
Cash equivalents carried at fair value	$100,000,000	$26,501,000	$8,001,000

Schedule_of_Property_and_Equip

Schedule of Property and Equipment, Net (Detail) (USD $)	Sep. 30, 2014	Dec. 31, 2013	Dec. 31, 2012
In Thousands, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013	Dec. 31, 2012
Property, Plant and Equipment [Line Items]
Property and equipment, gross		$71	$54
Less: Accumulated depreciation		-34	-22
Property and equipment, net	69	37	32
Office Equipment [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross		27	10
Furniture and Fixtures [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross		$44	$44

Property_and_Equipment_net_Add

Property and Equipment, net - Additional Information (Detail) (USD $)	9 Months Ended		12 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Property Plant And Equipment Capitalized Interest Costs [Abstract]
Depreciation expense	$10	$8	$12	$11	$4

Accrued_Expenses_Schedule_of_A

Accrued Expenses - Schedule of Accrued Expenses (Detail) (USD $)	Sep. 30, 2014	Dec. 31, 2013	Dec. 31, 2012
In Thousands, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013	Dec. 31, 2012
Payables and Accruals [Abstract]
Accrued licensing milestones fees	$6,700
Accrued research and development expenses	1,759	616	1,558
Accrued payroll and related expenses	741	49	74
Accrued professional fees	542	196	62
Accrued interest	51
Accrued other	92	39	5
Accrued expenses	$9,885	$900	$1,699

Convertible_Promissory_Notes_A

Convertible Promissory Notes - Additional Information (Detail) (USD $)	9 Months Ended		12 Months Ended			1 Months Ended
In Thousands, except Share data, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Jan. 31, 2013	Nov. 30, 2012	Aug. 31, 2012
Debt Instrument [Line Items]
Promissory notes convertible threshold percentage of preferred stock price			90.00%
Number of redeemable convertible preferred stock issued	0		94,483,404	73,991,017
Proceeds from issuance of redeemable convertible preferred stock	$442	$5,955	$40,799	$16,057	$10,069
Series D Preferred Stock [Member]
Debt Instrument [Line Items]
Promissory notes principal amount							6,000
Number of redeemable convertible preferred stock issued			16,011,162	11,629,248		4,381,914	6,653,988
Proceeds from issuance of redeemable convertible preferred stock						5,956	9,044
Outstanding principal and accrued interest amount converted							6,086
Outstanding principal and accrued interest shares converted							4,975,260
Minimum [Member]
Debt Instrument [Line Items]
Proceeds from issuance of preferred stock			10,000
Convertible Notes Payable [Member]
Debt Instrument [Line Items]
Promissory notes principal amount							$6,000	$6,000
Annual interest rate			8.00%

Redeemable_Convertible_Preferr2

Redeemable Convertible Preferred Stock - Additional Information (Detail) (USD $)	9 Months Ended		12 Months Ended			1 Months Ended
In Thousands, except Share data, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Feb. 29, 2012	Jan. 31, 2013	Nov. 30, 2012	Nov. 30, 2013
Temporary Equity [Line Items]
Preferred stock, shares authorized	0		99,292,610	78,372,931
Preferred stock, par value	$0.00		$0.00	$0.00
Preferred stock, shares issued	0		94,483,404	73,991,017
Proceeds from issuance of shares	$442	$5,955	$40,799	$16,057	$10,069
Stock issuance cost	2,312	165	196
Percentage of redeemable preferred stock voting for conversion			70.00%
Proceeds from public offering	102,672
Convertible preferred stock, conversion ratio			6.28
Series C Preferred Stock [Member]
Temporary Equity [Line Items]
Preferred stock, shares authorized			16,732,284	16,732,284
Preferred stock, shares issued			16,732,284	16,732,284	8,923,884	7,808,400
Convertible preferred stock, original issue price			$0.91		$0.91	$0.91
Proceeds from issuance of shares					8,086	7,075
Stock issuance cost				8	33	8
Percentage of redeemable preferred stock voting for conversion			70.00%
Convertible preferred stock, conversion price			$5.69
Series D Preferred Stock [Member]
Temporary Equity [Line Items]
Preferred stock, shares authorized			16,011,162	16,011,162
Preferred stock, shares issued			16,011,162	11,629,248			4,381,914	6,653,988
Convertible preferred stock, original issue price			$1.36				$1.36	$1.36
Proceeds from issuance of shares							5,956	9,044
Stock issuance cost			1	54			1	54
Promissory notes principal amount								6,000
Promissory notes accrued interest amount								86
Promissory notes accrued interest amount converted into shares								4,975,260
Percentage of redeemable preferred stock voting for conversion			65.00%
Convertible preferred stock, conversion price			$8.54
Series E Preferred Stock [Member]
Temporary Equity [Line Items]
Preferred stock, shares authorized			20,919,679
Preferred stock, shares issued			16,110,473						16,110,473
Convertible preferred stock, original issue price			$2.17						$2.17
Proceeds from issuance of shares									35,000
Stock issuance cost			156						156
Convertible preferred stock, conversion price			$13.64
Series A Preferred Stock [Member]
Temporary Equity [Line Items]
Preferred stock, shares authorized			5,363,239	5,363,239
Preferred stock, shares issued			5,363,239	5,363,239
Convertible preferred stock, original issue price			$0.42
Percentage of redeemable preferred stock voting for conversion			70.00%
Convertible preferred stock, conversion price			$2.63
Series B Preferred Stock [Member]
Temporary Equity [Line Items]
Preferred stock, shares authorized			40,266,246	40,266,246
Preferred stock, shares issued			40,266,246	40,266,246
Convertible preferred stock, original issue price			$0.76
Stock issuance cost					9
Percentage of redeemable preferred stock voting for conversion			70.00%
Convertible preferred stock, conversion price			$4.74
Redeemable Preferred Stock [Member]
Temporary Equity [Line Items]
Percentage of redeemable preferred stock voting for conversion			70.00%
Proceeds from public offering			$35,000
Preferred stock, conversion terms			Each share of Redeemable Preferred Stock is convertible into common stock at the option of the stockholder at any time after the date of issuance. Each share of the preferred stock will automatically be converted into shares of common stock, at the applicable Series A, Series B, Series C, Series D and Series E redeemable convertible preferred stock conversion ratio then in effect, upon a qualified public offering with net proceeds of not less than $35,000.
Redemption date			22-Nov-17
Number of annual installments			3

Schedule_of_Redeemable_Preferr

Schedule of Redeemable Preferred Stock (Detail) (USD $)	Sep. 30, 2014	Dec. 31, 2013	Dec. 31, 2012	Feb. 29, 2012	Dec. 31, 2011	Jan. 31, 2013	Nov. 30, 2012	Nov. 30, 2013
Schedule Of Redeemable Convertible Preferred Stock [Line Items]
Preferred Shares Authorized	0	99,292,610	78,372,931
Preferred Shares Issued	0	94,483,404	73,991,017
Preferred Shares Outstanding	0	94,483,404	73,991,017
Liquidation Preference		$104,588,000	$63,629,000
Carrying Value		103,797	62,785
Common Stock Issuable Upon Conversion		15,045,125	11,782,007
Series A Preferred Stock [Member]
Schedule Of Redeemable Convertible Preferred Stock [Line Items]
Preferred Shares Authorized		5,363,239	5,363,239
Preferred Shares Issued		5,363,239	5,363,239
Preferred Shares Outstanding		5,363,239	5,363,239
Liquidation Preference		2,250,000	2,250,000
Carrying Value		2,229	2,222
Common Stock Issuable Upon Conversion		854,018	854,018
Series B Preferred Stock [Member]
Schedule Of Redeemable Convertible Preferred Stock [Line Items]
Preferred Shares Authorized		40,266,246	40,266,246
Preferred Shares Issued		40,266,246	40,266,246
Preferred Shares Outstanding		40,266,246	40,266,246
Liquidation Preference		30,402,000	30,402,000
Carrying Value		30,351	30,335
Common Stock Issuable Upon Conversion		6,411,822	6,411,822
Series C Preferred Stock [Member]
Schedule Of Redeemable Convertible Preferred Stock [Line Items]
Preferred Shares Authorized		16,732,284	16,732,284
Preferred Shares Issued		16,732,284	16,732,284	7,808,400	8,923,884
Preferred Shares Outstanding		16,732,284	16,732,284
Liquidation Preference		15,161,000	15,161,000
Carrying Value		15,144	15,137
Common Stock Issuable Upon Conversion		2,664,376	2,664,376
Series D Preferred Stock [Member]
Schedule Of Redeemable Convertible Preferred Stock [Line Items]
Preferred Shares Authorized		16,011,162	16,011,162
Preferred Shares Issued		16,011,162	11,629,248			4,381,914	6,653,988
Preferred Shares Outstanding		16,011,162	11,629,248
Liquidation Preference		21,775,000	15,816,000
Carrying Value		21,226	15,091
Common Stock Issuable Upon Conversion		2,549,548	1,851,791
Series E Preferred Stock [Member]
Schedule Of Redeemable Convertible Preferred Stock [Line Items]
Preferred Shares Authorized		20,919,679
Preferred Shares Issued		16,110,473						16,110,473
Preferred Shares Outstanding		16,110,473
Liquidation Preference		35,000,000
Carrying Value		$34,847
Common Stock Issuable Upon Conversion		2,565,361

Common_Stock_Additional_Inform

Common Stock - Additional Information (Detail) (USD $)	12 Months Ended	9 Months Ended
	Dec. 31, 2013	Sep. 30, 2013	Sep. 30, 2014	Dec. 31, 2012
	Vote	Sep. 30, 2013	Sep. 30, 2014	Dec. 31, 2012
Changes In Equity And Comprehensive Income Line Items [Line Items]
Common stock, shares authorized	115,000,000		115,000,000	100,000,000
Common stock, par value	$0.00		$0.00	$0.00
Votes entitled to, per share	1
Dividends declared	$0
Shares of common stock reserved	16,726,699
Common Stock [Member]
Changes In Equity And Comprehensive Income Line Items [Line Items]
Reacquired and retired restricted common stock	-6,635
Common Stock [Member] \| Restricted Stock [Member]
Changes In Equity And Comprehensive Income Line Items [Line Items]
Reacquired and retired restricted common stock	6,635	6,635

StockBased_Awards_Additional_I

Stock-Based Awards - Additional Information (Detail) (USD $)	0 Months Ended	12 Months Ended			9 Months Ended	0 Months Ended
In Thousands, except Share data, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Sep. 30, 2014	Sep. 01, 2014	Dec. 31, 2010	Jun. 05, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Aggregate intrinsic value of stock options exercised		$0	$12	$0
Proceeds from exercise of stock options			13
Weighted average grant-date fair value of stock options granted		$1.83	$0	$1.07
Unrecognized stock-based compensation cost	6,224	1,334			6,224
Stock-based compensation recognized weighted average period	3 years 4 months 24 days	3 years 7 months 6 days
Shares of common stock reserved for issuance		16,726,699
Common Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock options granted					529,565
Service Based Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Outstanding unvested service-based stock options held by nonemployees		17,513
Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Outstanding unvested service-based stock options held by nonemployees		796
Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Outstanding unvested service-based stock options held by nonemployees			10,615	24,548			38,481
Aggregate intrinsic value of restricted stock awards vested during the period		$38	$22	$22
Nonemployee Service Based Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of outstanding unvested shares held by nonemployees	17,513				17,513
Nonemployee Performance Based Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of outstanding unvested shares held by nonemployees	796				796
Employee Stock Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock options granted					527,973
Consultant [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock options granted					1,592
2006 Stock Option Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of exercise price per share of stock options in fair market value of share of common stock		100.00%			100.00%
Shares vesting period under stock options plan		4 years
Shares expiration period under stock option plan		10 years
Number of shares of common stock that could be issued under stock option plan	1,889,150	1,889,150			1,889,150
Common stock available for issuance		371,244
Shares of common stock reserved for issuance	168,221				168,221
2006 Stock Option Plan [Member] \| Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares vesting period under stock options plan		10 years			10 years
2014 Stock Option and Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares of common stock reserved for issuance	2,168,221				2,168,221
Percentage of outstanding shares of common stock					4.00%
2014 Employee Stock Purchase Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock available for issuance	265,000				265,000
Shares of common stock reserved for issuance								265,000
Commencement date of first offering period						1-Sep-14
2014 Employee Stock Purchase Plan [Member] \| Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Purchase price of closing market price of the company's common stock offering period						85.00%

Assumptions_used_to_Determine_

Assumptions used to Determine Fair Value of Stock Options Granted (Detail)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2011
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Risk-free interest rate	1.12%	1.41%
Expected term (in years)	6 years 3 months	6 years 3 months
Expected volatility	85.00%	78.00%
Expected dividend yield	0.00%	0.00%

Summary_of_Stock_Options_Activ

Summary of Stock Options Activity (Detail) (USD $)	12 Months Ended
In Thousands, except Share data, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Shares issuable under options
Shares issuable under options, beginning balance	591,427	916,094	440,301
Shares issuable under options, granted	718,903	7,961	475,793
Shares issuable under options, exercised		-16,069
Shares issuable under options, forfeited		-316,559
Shares issuable under options, ending balance	1,310,330	591,427	916,094	440,301
Shares issuable under options, options vested and expected to vest	1,310,330
Shares issuable under options, options exercisable	657,317
Weighted-average exercise price
Weighted-average exercise price, beginning balance	$1	$1.19	$0.75
Weighted-average exercise price, granted	$2.64	$1.57	$1.57
Weighted-average exercise price, exercised		$0.88
Weighted-average exercise price, forfeited		$1.57
Weighted-average exercise price, ending balance	$1.88	$1	$1.19	$0.75
Weighted-average exercise price, options vested and expected to vest	$1.88
Weighted-average exercise price, options exercisable	$1.26
Weighted-average remaining contractual life
Weighted-average remaining contractual life	7 years 9 months 18 days	7 years 1 month 6 days	8 years 8 months 12 days	8 years 6 months
Weighted-average remaining contractual life, options vested and expected to vest	7 years 9 months 18 days
Weighted-average remaining contractual life, options exercisable	6 years 7 months 6 days
Aggregate intrinsic value
Aggregate intrinsic value, beginning balance	$342	$354		$216
Aggregate intrinsic value, ending balance	10,185	342	354
Aggregate intrinsic value, options vested and expected to vest	10,185
Aggregate intrinsic value, options exercisable	$5,543

Summary_of_Restricted_Stock_Ac

Summary of Restricted Stock Activity (Detail) (Restricted Stock [Member], USD $)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares, beginning balance	10,615	24,548	38,481
Number of shares, issued	0	0	0
Number of shares, vested	-3,980	-13,933	-13,933
Number of shares, forfeited	-6,635
Number of shares, ending balance		10,615	24,548
Weighted average grant-date fair value, beginning balance	$0.82	$0.82	$0.82
Weighted average grant-date fair value, issued	$0	$0	$0
Weighted average grant-date fair value, vested	$0.75	$0.75	$0.75
Weighted average grant-date fair value, forfeited	$0.82
Weighted average grant-date fair value, ending balance		$0.82	$0.82

StockBased_Awards_Summary_of_S

Stock-Based Awards - Summary of Stock-Based Compensation Expense Related to Stock Options and Restricted Common Stock (Detail) (USD $)	9 Months Ended		12 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation expense	$910	$252	$395	$121	$80
Research and Development [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation expense	259	109	176	68	30
General and Administrative [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation expense	$651	$143	$219	$53	$50

Computation_of_Basic_and_Dilut

Computation of Basic and Diluted Earnings Per Share (Detail) (USD $)	9 Months Ended		12 Months Ended
In Thousands, except Share data, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Numerator:
Net loss	($25,547)	($10,181)	($14,027)	($13,880)	($13,157)
Accretion of redeemable convertible preferred stock to redemption value	-92	-160	-213	-67	-53
Net loss attributable to common stockholders	($25,639)	($10,341)	($14,240)	($13,947)	($13,210)
Denominator:
Weighted average common shares outstanding, basic and diluted	8,618,793	728,862	729,001	709,678	688,946
Net loss per share attributable to common stockholders, basic and diluted	($2.97)	($14.19)	($19.53)	($19.65)	($19.17)

Summary_of_Common_Stock_Equiva

Summary of Common Stock Equivalents Outstanding (Detail)	9 Months Ended		12 Months Ended
Summary of Common Stock Equivalents Outstanding (Detail)	Sep. 30, 2014	Sep. 30, 2013	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Dilutive Securities Included And Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Securities excluded from computation of earnings per share	1,839,895	79,656,195	1,310,330	602,042	940,642
Options to purchase common stock [Member]
Dilutive Securities Included And Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Securities excluded from computation of earnings per share	1,839,895	1,283,264	1,310,330	591,427	916,094
Unvested Restricted Common Stock [Member]
Dilutive Securities Included And Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Securities excluded from computation of earnings per share				10,615	24,548

Commitments_and_Contingencies_1

Commitments and Contingencies - Additional Information (Detail) (USD $)	9 Months Ended		12 Months Ended			0 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	15-May-14
Commitment And Contingencies [Line Items]
Future minimum commitments	$660		$64
Operating lease, rental expense	104	87	105	129	102
Laboratory Space [Member]
Commitment And Contingencies [Line Items]
Future minimum commitments			0
Development Based Milestones [Member]
Commitment And Contingencies [Line Items]
Milestone payments due	6,700
Pre Commercialization Milestones [Member]
Commitment And Contingencies [Line Items]
Milestone payments	12,250		18,950
Product Commercialization Milestones [Member]
Commitment And Contingencies [Line Items]
Milestone payments	12,500		12,500
Subsequent Licensed Product [Member]
Commitment And Contingencies [Line Items]
Licensing fees per product maximum	$1,250		$1,250
Office Two [Member]
Commitment And Contingencies [Line Items]
Lease expiration date	31-Jul-17
Lease extension period						3 years
Office Space [Member]
Commitment And Contingencies [Line Items]
Lease expiration date			31-Jul-14
Lease extension period			6 months
Office Space [Member] \| Before Amendment [Member]
Commitment And Contingencies [Line Items]
Lease expiration date			31-Jul-13
Office Space [Member] \| After Amendment [Member]
Commitment And Contingencies [Line Items]
Lease expiration date			31-Jan-14

Commitments_and_Contingencies_2

Commitments and Contingencies - Schedule of Future Minimum Lease Payments for Operating Leases (Detail) (USD $)	Sep. 30, 2014	Dec. 31, 2013
In Thousands, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Commitments and Contingencies Disclosure [Abstract]
Remainder of 2014	$57
2014		64
2015	229
2016	235
2017	139
Total	$660	$64

Research_and_Development_Expen

Research and Development Expenses Related to License Agreements (Detail) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Commitments and Contingencies Disclosure [Abstract]
Licensing, milestone and license maintenance fees	$150	$1,055

Income_Taxes_Additional_Inform

Income Taxes - Additional Information (Detail) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Income Taxes Disclosure [Line Items]
Income tax benefit	$0	$0	$0
Net operating loss carryforwards, additional amount	16
Uncertain tax position	0
Gross deferred tax asset	30,357	24,006
Unrecognized tax benefits		0
Domestic Tax Authority [Member]
Income Taxes Disclosure [Line Items]
Net operating loss carryforwards	10,548
Net operating loss carryforwards begin to expire	2026
Research and development tax credit carryforwards	4,706
Research and development tax credit carryforwards begin to expire	2026
State and Local Jurisdiction [Member]
Income Taxes Disclosure [Line Items]
Net operating loss carryforwards	8,226
Net operating loss carryforwards begin to expire	2014
Research and development tax credit carryforwards	$1,322
Research and development tax credit carryforwards begin to expire	2021

Reconciliation_of_Federal_Stat

Reconciliation of Federal Statutory Income Tax Rate (Detail)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Income Tax Disclosure [Abstract]
Federal statutory income tax rate	-34.00%	-34.00%	-34.00%
Federal and state research and development tax credit	-9.00%	-1.20%	-6.40%
Orphan drug tax credit	-3.10%
State taxes, net of federal benefit	-4.00%	-5.00%	-5.40%
Meals and entertainment			0.10%
Stock-based compensation expense	0.60%	0.20%	0.20%
Nondeductible Australia research and development expenses	4.10%	1.80%
Change in deferred tax asset valuation allowance	45.40%	38.20%	45.50%
Effective income tax rate	0.00%	0.00%	0.00%

Schedule_of_Net_Deferred_tax_A

Schedule of Net Deferred tax Assets (Detail) (USD $)	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Income Tax Disclosure [Abstract]
Accrued expenses	$18	$46
Other temporary differences	2	1
Total current deferred tax assets	20	47
Noncurrent deferred tax assets:
Capitalized research and development expenses	19,856	16,676
Net operating loss carryforwards	4,021	3,209
Tax credit carryforwards	5,579	3,656
Capitalized legal expenses	790	385
Stock-based compensation	91	33
Total noncurrent deferred tax assets	30,337	23,959
Total gross deferred tax assets	30,357	24,006
Valuation allowance	-30,357	-24,006	-18,744	-12,748
Net deferred tax assets	$0	$0

Summary_of_Changes_in_the_Valu

Summary of Changes in the Valuation Allowance for Deferred Tax Assets (Detail) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Income Tax Disclosure [Abstract]
Valuation allowance as of beginning of year	$24,006	$18,744	$12,748
Decreases recorded as benefit to income tax provision	0	0	0
Increases recorded to income tax provision	6,351	5,262	5,996
Valuation allowance as of end of year	$30,357	$24,006	$18,744

Retirement_Plan_Additional_Inf

Retirement Plan - Additional Information (Detail) (USD $)	9 Months Ended		12 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Compensation and Retirement Disclosure [Abstract]
Percentage of employer's contribution on employee's base salary	2.00%		2.00%
Contribution expense	$43	$20	$26	$16	$15

Australia_Research_and_Develop1

Australia Research and Development Tax Incentive - Additional Information (Detail) (USD $)	9 Months Ended		12 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013	Dec. 31, 2013	Dec. 31, 2012
Operating Loss Carryforwards [Line Items]
Percentage of refundable tax incentive	45.00%		45.00%
Reduction to research and development expenses	($368)	$1,230	$1,237	$630
Unrealized foreign currency exchange (gains) losses	31	169	250
Tax incentive receivable	1,218		1,617
Australia [Member]
Operating Loss Carryforwards [Line Items]
Tax incentive receivable	1,218		1,617	630
Percentage of reduction in research and development costs	45.00%		45.00%
Tax Incentive [Member]
Operating Loss Carryforwards [Line Items]
Unrealized foreign currency exchange (gains) losses	$31	$169	$250

Related_Party_Transactions_Add

Related Party Transactions - Additional Information (Detail) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Commitment, Contingency And Related Party Transactions [Abstract]
Related party transaction, expenses from transactions with related party	$80	$80	$18
Related party transaction, revenues from transactions with related party		$500

Subsequent_Events_Additional_I

Subsequent Events - Additional Information (Detail) (USD $)	9 Months Ended		12 Months Ended			1 Months Ended	0 Months Ended	1 Months Ended
In Thousands, except Share data, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Nov. 30, 2013	Jun. 05, 2014	Feb. 28, 2014
Subsequent Event [Line Items]
Redeemable convertible preferred stock, issued	0		94,483,404	73,991,017
Proceeds from issuance of redeemable convertible preferred stock	$442	$5,955	$40,799	$16,057	$10,069
Redeemable convertible preferred stock, issuance cost	2,312	165	196
Series E Preferred Stock [Member]
Subsequent Event [Line Items]
Redeemable convertible preferred stock, issued			16,110,473			16,110,473
Redeemable convertible preferred stock, issuance price			$2.17			$2.17
Proceeds from issuance of redeemable convertible preferred stock						35,000
Redeemable convertible preferred stock, issuance cost			156			156
Subsequent Event [Member]
Subsequent Event [Line Items]
Redeemable convertible preferred stock, conversion ratio							1-for-6.28
Subsequent Event [Member] \| Series E Preferred Stock [Member]
Subsequent Event [Line Items]
Redeemable convertible preferred stock, issued								204,101
Redeemable convertible preferred stock, issuance price								$2.17
Proceeds from issuance of redeemable convertible preferred stock								443
Redeemable convertible preferred stock, issuance cost								$1

Summary_of_Significant_Account3

Summary of Significant Accounting Policies - Summary of Common Stock Equivalents Outstanding (Detail)	9 Months Ended		12 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total options and redeemable convertible preferred stock exercisable or convertible into common stock	1,839,895	79,656,195	1,310,330	602,042	940,642
Options to purchase common stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total options and redeemable convertible preferred stock exercisable or convertible into common stock	1,839,895	1,283,264	1,310,330	591,427	916,094
Redeemable convertible preferred stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total options and redeemable convertible preferred stock exercisable or convertible into common stock		78,372,931

Notes_Payable_Additional_Infor

Notes Payable - Additional Information (Detail) (USD $)	9 Months Ended	12 Months Ended	0 Months Ended
Notes Payable - Additional Information (Detail) (USD $)	Sep. 30, 2014	Dec. 31, 2012	Mar. 31, 2014	Dec. 31, 2013
Debt Instrument [Line Items]
Line of credit facility description	The Company was obligated to make monthly, interest-only payments on any term loans funded under the Credit Facility until December 1, 2014 and, thereafter, to pay 36 consecutive, equal monthly installments of principal and interest from January 1, 2015 through December 1, 2017. As per the terms of the agreement, in June 2014, upon the completion of the Companybs IPO, the term of monthly, interest-only payments were extended until June 1, 2015.
Interest expense	$658,000	$97,000
Covenants under credit facility	0
Interest expense on credit facility	658,000
Credit facility, amount outstanding				0
Credit Facility [Member]
Debt Instrument [Line Items]
Credit facility initiation date	31-Mar-14
Maximum line of credit			20,000,000
Credit facility maturity date	1-Dec-17
Line of credit facility description	On March 31, 2014, the Company received proceeds of $7,500 from the issuance of promissory notes under the Term Loan A. Of the additional $12,500 amount that is available, $7,500 (bTerm Loan Bb) was available to be drawn down until September 30, 2014 and $5,000 (bTerm Loan Cb) was available to be drawn down for a 30-day period upon the completion of the Companybs IPO that occurred in June 2014. The Company elected not to draw down Term Loans B or C and these amounts are no longer available to the Company. All promissory notes issued under the Credit Facility are collateralized by substantially all of the Companybs personal property, other than its intellectual property.
Line of credit facility annual interest rate	8.10%
Line of credit facility additional fee percentage	6.00%
Additional interest expense for IPO	225,000
Sale of voting equity threshold	50.00%
Credit facility default amount	250,000
Credit Facility [Member] \| Term Loan A [Member]
Debt Instrument [Line Items]
Current line of credit			7,500,000
Proceeds from issuance of promissory notes			7,500,000
Charges to interest expense of debt outstanding	450,000
Net of debt discount			114,000
Deferred financing costs			49,000
Credit Facility [Member] \| Term Loan A [Member] \| Debt Discount And Finance Costs [Member]
Debt Instrument [Line Items]
Interest expense	36,000
Credit Facility [Member] \| Term Loan B And C [Member]
Debt Instrument [Line Items]
Current line of credit			12,500,000
Additional line of credit			12,500,000
Credit Facility [Member] \| Term Loan B [Member]
Debt Instrument [Line Items]
Additional line of credit	7,500,000
Credit Facility [Member] \| Term Loan C [Member] \| Qualified Ipo [Member]
Debt Instrument [Line Items]
Additional line of credit	$5,000,000

Notes_Payable_Schedule_of_Esti

Notes Payable - Schedule of Estimated Future Principal Payments Due under Term Loan (Detail) (Term Loan A [Member], USD $)	Sep. 30, 2014
In Thousands, unless otherwise specified	Sep. 30, 2014
Term Loan A [Member]
Line of Credit Facility [Line Items]
Remainder of 2014
2015	1,381
2016	2,936
2017	3,183
Total	$7,500

Stockholders_Equity_Additional

Stockholders' Equity - Additional Information (Detail) (USD $)	9 Months Ended	12 Months Ended	0 Months Ended	9 Months Ended
In Thousands, except Share data, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013	Jun. 24, 2014	Sep. 30, 2013	Dec. 31, 2012
Reverse Stock split Ratio		6.28
Net proceeds from initial public offering	$102,672
Redeemable convertible preferred stock converted into common stock shares		15,045,125			11,782,007
Preferred stock, shares authorized	5,000,000	0
Preferred stock, par value	$0.00	$0.00
Common stock, shares authorized	115,000,000	115,000,000			100,000,000
Common stock, par value	$0.00	$0.00			$0.00
Common Stock [Member]
Reverse stock split, description	Company effected a 1-for-6.28 reverse stock split of its issued and outstanding shares of common stock and a proportional adjustment to the existing conversion ratios for each series of redeemable convertible preferred stock.
Reacquired and retired shares of restricted common stock		-6,635
Common Stock [Member] \| IPO [Member]
Reverse Stock split Ratio	0.1592
Initial public offering, common stock issued, shares			6,900,000
Initial public offering, common stock issued per share			$16
Net proceeds from initial public offering			102,672
Offering costs			$2,508
Redeemable convertible preferred stock converted into common stock shares	15,077,621
Common Stock [Member] \| Restricted Stock [Member]
Reacquired and retired shares of restricted common stock		6,635		6,635