Consolidated Statements of Convertible Preferred Stock and Stockholders' Equity (Deficit) - 9 months ended Sep. 30, 2015 - USD ($) $ in Thousands	Total	Convertible Preferred Stock Series A, A-2, B, C, D and D-1 [Member]	Convertible Preferred Stock Series A, A-2, B, C, D and D-1 [Member] Series D Convertible Preferred Stock [Member]	Common Stock [Member]	Additional Paid-in Capital [Member]	Accumulated Deficit [Member]	Accumulated Other Comprehensive Income [Member]
Stockholders' equity (deficit), value, beginning balance at Dec. 31, 2014	$ (26,721)				$ 1,104	$ (27,832)
Stockholders' equity (deficit), shares, beginning balance at Dec. 31, 2014	6,890,250			6,890,250
Stockholders' equity (deficit), par value, beginning balance at Dec. 31, 2014	$ 0.001			$ 7
Convertible preferred stock, value, beginning balance at Dec. 31, 2014		$ 136,077
Convertible preferred stock, shares, beginning balance at Dec. 31, 2014		22,866,987
Issuance costs of convertible preferred stock			$ (24)
Issuance of common stock upon exercise of stock options, value	$ 91				91
Issuance of common stock upon exercise of stock options, shares	206,720			206,720
Issuance of common stock upon exercise of common stock warrants, value	$ 169				168
Issuance of common stock upon exercise of common stock warrants, shares				546,672
Issuance of common stock upon exercise of common stock warrants, par value				$ 1
Issuance of common stock upon completion of initial public offering, net of offering costs, value	139,267				139,259
Issuance of common stock upon completion of initial public offering, net of offering costs, shares				8,545,138
Issuance of common stock upon completion of initial public offering, net of offering costs, par value				$ 8
Stock-based compensation expense	6,907				6,907
Reclassification of preferred stock warrant liability	1,589				1,589
Conversion of convertible preferred stock listing of the Company's common stock on the NASDAQ , value	136,053	$ (136,053)			136,030
Conversion of convertible preferred stock upon listing of the Company's common stock on the NASDAQ , shares		(22,866,987)		22,866,987
Conversion of convertible preferred stock upon listing of the Company's common stock on the NASDAQ , par value				$ 23
Unrealized gain on investments	(10)						$ (10)
Net loss	(35,146)					(35,146)
Stockholders' equity (deficit), value, ending balance at Sep. 30, 2015	$ 222,199				$ 285,148	$ (62,978)	$ (10)
Stockholders' equity (deficit), shares, ending balance at Sep. 30, 2015	39,055,767			39,055,767
Stockholders' equity (deficit), par value, ending balance at Sep. 30, 2015	$ 0.001			$ 39
Convertible preferred stock, value, ending balance at Sep. 30, 2015		$ 0
Convertible preferred stock, shares, ending balance at Sep. 30, 2015		0