Consolidated Statements of Convertible Preferred Stock and Stockholders' Equity (Deficit) - USD ($) $ in Thousands	Total	Convertible Preferred Stock Series A, A-2, B, C, D and D-1 [Member]	Series B Convertible Preferred Stock [Member]	Series C Convertible Preferred Stock [Member]	Series D and D-1 Convertible Preferred Stock [Member]	Series D Convertible Preferred Stock [Member]	Common Stock [Member]	Additional Paid-in Capital [Member]	Accumulated Other Comprehensive Income [Member]	Accumulated Deficit [Member]
Stockholders' (deficit), value, beginning balance at Dec. 31, 2012	$ (4,348)						$ 7			$ (4,355)
Stockholders' (deficit), shares, beginning balance at Dec. 31, 2012							7,590,000
Convertible preferred stock, value, beginning balance at Dec. 31, 2012		$ 10,708
Convertible preferred stock, shares, beginning balance at Dec. 31, 2012		10,478,189
Repurchase of unvested restricted common stock							(735,000)
Stock-based compensation expense	209							$ 209
Accretion of convertible preferred stock to redemption value	(875)	$ 875								(666)
Accretion of convertible preferred stock to redemption value, impact on permanent equity								(209)
Net loss	(6,102)									(6,102)
Stockholders' (deficit), value, ending balance at Dec. 31, 2013	(11,116)						$ 7			(11,123)
Stockholders' (deficit), shares, ending balance at Dec. 31, 2013							6,855,000
Convertible preferred stock, value, ending balance at Dec. 31, 2013		$ 11,583
Convertible preferred stock, shares, ending balance at Dec. 31, 2013		10,478,189
Issuance of convertible preferred stock, net of issuance costs, value			$ 10,558	$ 47,813	$ 64,832
Issuance of convertible preferred stock, net of issuance costs, shares			4,831,359	3,946,328	3,611,111
Issuance of common stock upon exercise of stock options, value	5							5
Issuance of common stock upon exercise of stock options, shares							28,687
Issuance of common stock upon completion of initial public offering, net of offering costs, value	5							5
Issuance of common stock upon completion of initial public offering, net of offering costs, shares							6,563
Issuance of common stock upon exercise of common stock warrant, value	317							317
Stock-based compensation expense	2,068							2,068
Accretion of convertible preferred stock to redemption value	(1,291)	$ 1,291
Accretion of convertible preferred stock to redemption value, impact on permanent equity								(1,291)
Issuance costs of convertible preferred stock			$ (71)	$ (187)	$ (168)
Net loss	(16,709)									(16,709)
Stockholders' (deficit), value, ending balance at Dec. 31, 2014	$ (26,721)						$ 7	1,104		(27,832)
Stockholders' (deficit), shares, ending balance at Dec. 31, 2014	6,890,250						6,890,250
Convertible preferred stock, value, ending balance at Dec. 31, 2014		$ 136,077
Convertible preferred stock, shares, ending balance at Dec. 31, 2014		22,866,987
Issuance of common stock upon exercise of stock options, value	$ 93							93
Issuance of common stock upon exercise of stock options, shares	232,970						232,970
Issuance of common stock upon completion of initial public offering, net of offering costs, value	$ 139,267						$ 8	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 exercise of common stock warrant, value	169						$ 1	168
Issuance of common stock upon exercise of common stock warrant, shares							546,672
Stock-based compensation expense	9,694							9,694
Issuance costs of convertible preferred stock						$ (24)
Reclassification of preferred stock warrant liability	1,589							1,589
Conversion of convertible preferred stock upon listing, value	136,053	$ (136,053)					$ 23	136,030
Conversion of convertible preferred stock upon listing, shares		(22,866,987)					22,866,987
Unrealized gain on investments	30								$ 30
Net loss	(54,780)									(54,780)
Stockholders' (deficit), value, ending balance at Dec. 31, 2015	$ 205,394						$ 39	$ 287,937	$ 30	$ (82,612)
Stockholders' (deficit), shares, ending balance at Dec. 31, 2015	39,082,017						39,082,017
Convertible preferred stock, shares, ending balance at Dec. 31, 2015		0