Consolidated Statements of Convertible and Redeemable Convertible Preferred Stock and Stockholders' Equity (Deficit) - USD ($) $ in Thousands	Total	Convertible Preferred Stock [Member]	Redeemable Convertible Preferred Stock [Member]	Redeemable Convertible Preferred Stock [Member] Series C Redeemable Convertible Preferred Stock [Member]	Redeemable Convertible Preferred Stock [Member] Series D Redeemable Convertible Preferred Stock [Member]	Series C and D 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]	Subscription Receivable [Member]
Stockholders Equity, Beginning Balance at Dec. 31, 2013	$ (34,690)	$ 2,543	$ 34,005					$ 1						$ (34,691)	$ (1,159)
Stockholders Equity, Beginning Balance, Shares at Dec. 31, 2013		224,564	5,288,040					836,003
Issuance of common stock for exercise of stock options	305							$ 1		$ 304
Issuance of common stock for exercise of stock options, Shares								752,698
Repayment of stock subscription receivable															$ 1,159
Conversion of convertible securities, shares issued, value			$ 433
Conversion of convertible preferred stock to common stock upon initial public offering, Shares			82,927
Stock-based compensation	302									302
Adjustment to redemption value on redeemable convertible preferred stock	(49,849)		$ 49,849							(606)				(49,243)
Other comprehensive loss	(10)												$ (10)
Issuance of stock, value				$ 1,365	$ 56,180
Issuance of stock, shares				261,737	11,409,360
Net loss	(23,873)													(23,873)
Stockholders Equity, Ending Balance at Dec. 31, 2014	(107,815)	$ 2,543	$ 141,832					$ 2					(10)	(107,807)
Stockholders Equity, Ending Balance, Shares at Dec. 31, 2014		224,564	17,042,064					1,588,701
Issuance of common stock for exercise of stock options	18									18
Issuance of common stock for exercise of stock options, Shares								41,505
Conversion of convertible preferred stock to common stock upon initial public offering, Shares		(224,564)						252,817
Stock-based compensation	3,186									3,186
Vesting of early exercised stock options	90									90
Issuance of redeemable convertible preferred stock upon exercise of redeemable convertible preferred stock warrants			$ 8,976
Issuance of redeemable convertible preferred stock upon exercise of redeemable convertible preferred stock warrants, Shares			481,671
Issuance of redeemable convertible preferred stock upon net exercise of redeemable convertible preferred stock warrants 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 convertible preferred stock to common stock upon initial public offering	2,543	$ (2,543)								2,543
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 stock, value	143,549							$ 9		143,540
Issuance of stock, 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			750,946
Reclassification of other-than-temporary losses on short-term investments to net loss	10												$ 10
Net loss	(53,260)													(53,260)
Stockholders Equity, Ending Balance at Dec. 31, 2015	145,371							$ 30		679,528				(534,187)
Stockholders Equity, Ending Balance, Shares at Dec. 31, 2015								30,058,105
Issuance of common stock for exercise of stock options	211									211
Issuance of common stock for exercise of stock options, Shares								312,841
Stock-based compensation	5,510									5,510
Vesting of early exercised stock options	23									23
Net loss	(47,867)													(47,867)
Stockholders Equity, Ending Balance at Dec. 31, 2016	$ 103,248							$ 30		$ 685,272				$ (582,054)
Stockholders Equity, Ending Balance, Shares at Dec. 31, 2016								30,370,946