Consolidated Statements of Convertible Preferred Stock and Stockholders' Equity (Deficit) - USD ($) $ in Thousands	Total	Common Stock [Member]	Additional Paid-in Capital [Member]	Accumulated Other Comprehensive Income [Member]	Accumulated Deficit [Member]	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]
Stockholders' (deficit), value, beginning balance at Dec. 31, 2013	$ (11,116)	$ 7			$ (11,123)
Stockholders' (deficit), shares, beginning balance at Dec. 31, 2013		6,855,000
Convertible preferred stock, value, beginning balance at Dec. 31, 2013						$ 11,583
Convertible preferred stock, shares, beginning 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
Accretion of convertible preferred stock to redemption value, impact on permanent equity	(1,291)		(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
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
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	$ 23	136,030			$ (136,053)
Conversion of convertible preferred stock upon listing, shares		22,866,987				(22,866,987)
Unrealized gain (loss) 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
Issuance of common stock upon exercise of stock options, value	$ 2,138	$ 1	2,137
Issuance of common stock upon exercise of stock options, shares	1,273,736	1,273,736
Stock-based compensation expense	$ 16,857		16,857
Unrealized gain (loss) on investments	(179)			(179)
Net loss	(91,579)				(91,579)
Stockholders' (deficit), value, ending balance at Dec. 31, 2016	$ 132,631	$ 40	$ 306,931	$ (149)	$ (174,191)
Stockholders' (deficit), shares, ending balance at Dec. 31, 2016	40,355,753	40,355,753