Consolidated Statements of Redeemable Convertible Preferred Stock and Stockholders' Equity (Deficit) - USD ($) $ in Thousands	Total	IPO [Member]	Junior Convertible, and Senior Redeemable Convertible Preferred Stock [Member]	Redeemable Convertible Preferred Stock (Senior) [Member]	Redeemable Convertible Preferred Stock (Senior) [Member] Junior Convertible, and Senior Redeemable Convertible Preferred Stock [Member]	Common Stock [Member]	Common Stock [Member] IPO [Member]	Additional Paid-in Capital [Member]	Additional Paid-in Capital [Member] IPO [Member]	Additional Paid-in Capital [Member] Redeemable Convertible Preferred Stock (Senior) [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Accumulated Deficit [Member]
Beginning balance at Dec. 31, 2012			$ 26,176
Beginning balance (in shares) at Dec. 31, 2012			7,019,599
Increase (Decrease) in Temporary Equity [Roll Forward]
Private placement senior redeemable convertible preferred stock				$ 905	$ 50,996					$ 905
Private placement senior redeemable convertible preferred stock (shares)					6,693,808
Amortization of deemed dividend	$ (64)
Accretion to redemption value of redeemable convertible preferred stock	(6,303)		$ 6,303					$ (6,303)
Ending balance at Dec. 31, 2013			$ 83,475
Ending balance (in shares) at Dec. 31, 2013			13,713,407
Beginning balance at Dec. 31, 2012	(7,632)					$ 0		62,728			$ 88	$ (70,448)
Beginning balance (in shares) at Dec. 31, 2012						467,167
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net loss	(32,718)											(32,718)
Other comprehensive income (loss)	8										8
Exercise of stock options, net of repurchase liability	135					$ 0		135
Exercise of stock options, net of repurchase liability (shares)						139,071
Stock-based compensation	948							948
Ending balance at Dec. 31, 2013	(44,657)					$ 0		58,413			96	(103,166)
Ending balance (in shares) at Dec. 31, 2013						606,238
Increase (Decrease) in Temporary Equity [Roll Forward]
Private placement senior redeemable convertible preferred stock				$ 0	$ 18,167					$ 0
Private placement senior redeemable convertible preferred stock (shares)					2,296,016
Amortization of deemed dividend	(4,744)		$ 4,744					(4,744)
Accretion to redemption value of redeemable convertible preferred stock	(4,410)		4,410					(4,410)
Ending balance at Dec. 31, 2014			$ 0
Ending balance (in shares) at Dec. 31, 2014			0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net loss	(47,667)											(47,667)
Other comprehensive income (loss)	(7)										(7)
Exercise of stock options and change in stock option early exercise repurchase liability	956					$ 0		956
Exercise of stock options and change in stock option early exercise repurchase liability (shares)						142,041
Stock-based compensation	2,510							2,510
Initial public offering, net of issuance costs	32,853	$ 51,933				$ 0	$ 1	32,853	$ 51,932
Initial public offering, net of issuance costs (shares)						2,050,000	5,175,000
Conversion of redeemable convertible preferred stock to common stock	110,796		$ (110,796)			$ 1		110,795
Conversion of redeemable convertible preferred stock to common stock (shares)			(16,009,423)			16,009,423
Adjustment for fractional shares	0					$ 0		0			0	0
Adjustment for fractional shares (shares)						84
Ending balance at Dec. 31, 2014	97,563					$ 2		248,305			89	(150,833)
Ending balance (in shares) at Dec. 31, 2014						23,982,786
Increase (Decrease) in Temporary Equity [Roll Forward]
Amortization of deemed dividend	0
Accretion to redemption value of redeemable convertible preferred stock	0
Ending balance at Dec. 31, 2015			$ 0
Ending balance (in shares) at Dec. 31, 2015			0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net loss	(52,023)											(52,023)
Other comprehensive income (loss)	$ (9)										(9)
Exercise of stock options, net of repurchase liability (shares)	217,570
Exercise of stock options and change in stock option early exercise repurchase liability	$ 615					$ 0		615
Exercise of stock options and change in stock option early exercise repurchase liability (shares)						217,570
Stock-based compensation	4,029							4,029
Initial public offering, net of issuance costs	32,150					$ 1		32,149
Initial public offering, net of issuance costs (shares)						6,272,727
Ending balance at Dec. 31, 2015	$ 82,325					$ 3		$ 285,098			$ 80	$ (202,856)
Ending balance (in shares) at Dec. 31, 2015						30,473,083