Condensed Consolidated Statement of Convertible and Redeemable Convertible Preferred Stock and Stockholders' Equity (Deficit) - 9 months ended Sep. 30, 2015 - USD ($) $ in Thousands	Total	Convertible Preferred Stock [Member]	Redeemable Convertible Preferred Stock [Member]	Series B and B-1 Redeemable Convertible Preferred Stock [Member]	Common Stock [Member]	Common Stock [Member] Series C and D Redeemable Convertible Preferred Stock [Member]	Additional Paid-In Capital [Member]	Additional Paid-In Capital [Member] Series C and D Redeemable Convertible Preferred Stock [Member]	Additional Paid-In Capital [Member] Series B and B-1 Redeemable Convertible Preferred Stock [Member]	Accumulated Other Comprehensive Loss [Member]	Accumulated Deficit [Member]
Stockholders Equity, Beginning Balance at Dec. 31, 2014	$ (107,815)				$ 2					$ (10)	$ (107,807)
Stockholders Equity, Beginning Balance, Shares at Dec. 31, 2014					1,588,701
Temporary Equity, Beginning Balance at Dec. 31, 2014	$ 144,375	$ 2,543	$ 141,832
Temporary Equity, Beginning Balance, Shares at Dec. 31, 2014	17,266,628	224,564	17,042,064
Issuance of common stock for exercise of stock options	$ 18						$ 18
Issuance of common stock for exercise of stock options, Shares					41,505
Stock-based compensation	1,912						1,912
Vesting of early exercised stock options	75						75
Issuance of redeemable convertible preferred stock upon exercise of redeemable convertible preferred stock warrants for cash			$ 8,976
Issuance of redeemable convertible preferred stock upon exercise of redeemable convertible preferred stock warrants for cash, Shares			481,671
Issuance of redeemable convertible preferred stock upon net exercise of redeemable convertible preferred stock warrants and reclassification of preferred stock warrant liability upon initial public offering			$ 11,785
Issuance of redeemable convertible preferred stock upon net exercise of redeemable convertible preferred stock warrants and reclassification of preferred stock warrant liability upon initial public offering, Shares			390,032
Adjustment to redemption value on redeemable convertible preferred stock	(374,015)		$ 374,015				(895)				(373,120)
Conversion of preferred stock to common stock upon initial public offering	2,543	$ (2,543)					2,543
Conversion of preferred stock to common stock upon initial public offering, Shares		(224,564)			252,817
Conversion of redeemable convertible preferred stock to common stock upon initial public offering	536,608		$ (536,608)		$ 18		536,590
Conversion of redeemable convertible preferred stock to common stock upon initial public offering, Shares			(17,913,767)		18,109,136
Issuance of common stock in connection with initial public offering, net of issuance costs of $14.8 million	143,565				$ 9		143,556
Issuance of common stock in connection with initial public offering, net of issuance costs of $14.8 million, Shares					9,315,000
Redeemable convertible preferred stock dividend				$ (5,543)					$ (5,543)
Redeemable convertible preferred stock dividend, common stock issued						$ 1		$ (1)
Redeemable convertible preferred stock dividend						750,946
Reclassification of other-than-temporary losses on short-term investments to net loss	10									$ 10
Net loss	(41,802)										(41,802)
Stockholders Equity, Ending Balance at Sep. 30, 2015	$ 155,556				$ 30		$ 678,255				$ (522,729)
Stockholders Equity, Ending Balance, Shares at Sep. 30, 2015					30,058,105
Temporary Equity, Ending Balance at Sep. 30, 2015
Temporary Equity, Ending Balance, Shares at Sep. 30, 2015