Consolidated Statements of Stockholders' Equity (Deficit) Statement - USD ($) $ in Thousands	Total	Series E Convertible Preferred Stock	Series A Convertible Preferred Stock	Series C Convertible Preferred Stock	Convertible Preferred Stock	Convertible Preferred Stock Series E Convertible Preferred Stock	Convertible Preferred Stock Series A Convertible Preferred Stock	Convertible Preferred Stock Series C Convertible Preferred Stock	Common Stock	Additional paid-in capital	Additional paid-in capital Series E Convertible Preferred Stock	Additional paid-in capital Series A Convertible Preferred Stock	Additional paid-in capital Series C Convertible Preferred Stock	Accumulated deficit	Accumulated Other Comprehensive Income (Loss)
Beginning balance (in shares) at Dec. 31, 2012					26,704,174				6,161,665
Beginning balance at Dec. 31, 2012	$ 11,555				$ 67				$ 15	$ 98,580				$ (87,107)	$ 0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of Series E convertible preferred stock at $11.0315 (2012) and $11.0315 (2011) per share, net of issuance costs of $56 (2012) and $99 (2011) (in shares)						906,494
Issuance of Series E convertible preferred stock at $11.0315 (2012) and $11.0315 (2011) per share, net of issuance costs of $56 (2012) and $99 (2011)		$ 9,943				$ 2					$ 9,941
Issuance of convertible preferred stock upon exercise of warrants (in shares)								250,341
Issuance of convertible preferred stock upon exercise of warrants				$ 692				$ 0					$ 692
Reclassification of convertible preferred stock warrants upon exercise	1,755			1,755									1,755
Shares issued upon exercise of options (in shares)									1,072,661
Shares issued upon exercise of options	1,169								$ 3	1,166
Vesting of common stock from early exercised options (in shares)									185,143
Vesting of common stock from early exercised options	481								$ 0	481
Stock-based compensation	4,287									4,287
Net loss	(33,227)													(33,227)
Ending balance (in shares) at Dec. 31, 2013					27,861,009				7,419,469
Ending balance at Dec. 31, 2013	(3,345)				$ 69				$ 18	116,902				(120,334)	0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cashless exercise of convertible preferred stock warrants (in shares)							38,724
Cashless exercise of convertible preferred stock warrants			$ 0				$ 0					$ 0
Issuance of convertible preferred stock upon exercise of warrants (in shares)								327,795
Issuance of convertible preferred stock upon exercise of warrants				$ 907				$ 0					$ 907
Reclassification of convertible preferred stock warrants upon exercise	3,202									3,202
Issuance of common stock upon initial public offering, net of issuance costs (in shares)									8,625,000
Issuance of common stock upon initial public offering, net of issuance costs	74,798								$ 9	74,789
Conversion of preferred stock to common stock (in shares)					(28,227,528)				28,832,898
Conversion of preferred stock to common stock	0				$ (69)				$ 18	51
Conversion of preferred stock warrants to common stock warrants	611									611
Shares issued upon exercise of options (in shares)									915,563
Shares issued upon exercise of options	1,721								$ 1	1,720
Vesting of common stock from early exercised options (in shares)									113,500
Vesting of common stock from early exercised options	435								$ 0	435
Issuance of common stock upon vesting of RSUs (in shares)									187,699
Issuance of common stock upon vesting of RSUs	0								$ 0	0
Shares repurchased for tax withholdings on vesting of RSUs (in shares)									(65,221)
Shares repurchased for tax withholdings on vesting of RSUs	(316)									(316)
Stock-based compensation	10,697									10,697
Net loss	(30,555)													(30,555)
Ending balance (in shares) at Dec. 31, 2014					0				46,028,908
Ending balance at Dec. 31, 2014	58,155				$ 0				$ 46	208,998				(150,889)	0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Reclassification of convertible preferred stock warrants upon exercise	$ 0
Shares issued upon exercise of options (in shares)	678,533								678,533
Shares issued upon exercise of options	$ 1,524								$ 1	1,523
Common stock issued under ESPP	5,196								$ 1	5,195
Vesting of common stock from early exercised options (in shares)									27,000
Vesting of common stock from early exercised options	45								$ 0	45
Issuance of common stock upon vesting of RSUs (in shares)									1,580,206
Issuance of common stock upon vesting of RSUs	0								$ 2	(2)
Shares repurchased for tax withholdings on vesting of RSUs (in shares)									(523,366)
Shares repurchased for tax withholdings on vesting of RSUs	(3,158)								$ (1)	(3,157)
Modification for common stock warrants	59									59
Stock-based compensation	18,628									18,628
Unrealized Gain (Loss) on Investments	(61)														(61)
Net loss	(46,195)													(46,195)
Ending balance (in shares) at Dec. 31, 2015					0				49,017,293
Ending balance at Dec. 31, 2015	$ 34,193				$ 0				$ 49	$ 231,289				$ (197,084)	$ (61)