Consolidated Statements of Changes in Stockholders' Equity (Deficit) - USD ($) $ in Thousands	Common Stock.	Additional Paid-In Capital	Accumulated Deficit	Total
Balance at Dec. 31, 2012	$ 7	$ 5,483	$ (71,786)	$ (66,296)
Balance (in shares) at Dec. 31, 2012	7,386,133
Increase (Decrease) in Stockholders' Equity
Exercise of stock options	$ 1	324		325
Exercise of stock options (in shares)	290,604
Accretion of issuance costs on redeemable convertible preferred stock		(347)		(347)
Stock-based compensation expense		2,426		2,426
Repurchase of common shares		(69)	(110)	(179)
Repurchase of common shares (in shares)	(47,604)
Net loss			(27,953)	(27,953)
Balance at Dec. 31, 2013	$ 8	7,817	(99,849)	(92,024)
Balance (in shares) at Dec. 31, 2013	7,629,133
Increase (Decrease) in Stockholders' Equity
Exercise of stock options	$ 1	2,281		2,282
Exercise of stock options (in shares)	940,642
Grant of common stock		55		55
Grant in common stock (in shares)	5,000
Accretion of issuance costs on redeemable convertible preferred stock		(89)		(89)
Stock-based compensation expense		7,527		7,527
Conversion of redeemable convertible preferred stock to common stock	$ 23	98,113		98,136
Conversion of redeemable convertible preferred stock to common stock (in shares)	23,501,208
Conversion of Series D warrants to common stock warrants		821		821
Issuance of common stock, net of issuance costs	$ 9	100,293		100,302
Issuance of common stock, net of issuance costs ( in shares)	8,626,377
Exercise of warrants to purchase common stock (in shares)	32,709
Net loss			(28,999)	(28,999)
Balance at Dec. 31, 2014	$ 41	216,818	(128,848)	$ 88,011
Balance (in shares) at Dec. 31, 2014	40,735,069			40,735,069
Increase (Decrease) in Stockholders' Equity
Exercise of stock options	$ 1	5,335		$ 5,336
Exercise of stock options (in shares)	1,141,731
Stock-based compensation expense		11,749		11,749
Issuance of common stock in connection with settlement of restricted stock units, net of withholdings		(436)		(436)
Issuance of common stock in connection with settlement of restricted stock units, net of withholdings (in shares)	248,088
Issuance of common stock, net of issuance costs	$ 4	117,108		117,112
Issuance of common stock, net of issuance costs ( in shares)	3,625,000
Issuance of common stock award		750		750
Issuance of common stock award (in shares)	26,567
Net loss			(26,733)	(26,733)
Balance at Dec. 31, 2015	$ 46	$ 351,324	$ (155,581)	$ 195,789
Balance (in shares) at Dec. 31, 2015	45,776,455			45,776,455