Statements of Redeemable Convertible Preferred Stock and Stockholders' Equity (Deficit) - USD ($) $ in Thousands	Convertible Preferred Stock [Member] Series A Preferred Stock [Member]	Convertible Preferred Stock [Member] Series A-1 Preferred Stock [Member]	Convertible Preferred Stock [Member] Series B Preferred Stock [Member]	Convertible Preferred Stock [Member] Series C Preferred Stock [Member]	Convertible Preferred Stock [Member] Series D Preferred Stock [Member]	Common Stock [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	AOCI Attributable to Parent [Member]	Total
Balance (in shares) at Dec. 31, 2012	22,638,465	10,909,091	20,754,461	13,202,932		230,607
Balance at Dec. 31, 2012	$ 32,633	$ 16,526	$ 24,926	$ 16,201				$ (86,657)	$ 1	$ (86,656)
Accretion of Series A, A-1, B and C redeemable convertible preferred stock to redemption value	$ 1,597	$ 848	$ 2,475	$ 1,199			$ (174)	(5,945)		(6,119)
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period						9,298
Exercise of common stock options							19			19
Stock-based compensation expense							155			155
Unrealized gain (loss) on short term investments									(1)	(1)
Net loss								(7,912)		(7,912)
Balance (in shares) at Dec. 31, 2013	22,638,465	10,909,091	20,754,461	13,202,932		239,905
Balance at Dec. 31, 2013	$ 34,230	$ 17,374	$ 27,401	$ 17,400				(100,514)		(100,514)
Accretion of Series A, A-1, B and C redeemable convertible preferred stock to redemption value	$ 1,304	$ 691	$ 1,832	$ 948	$ 1,578		(335)	(6,018)		(6,353)
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period						31,356
Exercise of common stock options							59			59
Stock-based compensation expense							459			459
Unrealized gain (loss) on short term investments									(6)	(6)
Net loss								(3,342)		(3,342)
Balance (in shares) at Dec. 31, 2014						16,448,455
Balance at Dec. 31, 2014						$ 16	192,324	(109,874)	(6)	82,460
Issuance of Series D redeemable convertible preferred stock net of $6,639 discount associated with investors rights and obligations and issuance costs of $452 (in shares)					52,813,827
Issuance of Series D redeemable convertible preferred stock net of $6,639 discount associated with investors rights and obligations and issuance costs of $452					$ 24,078
Stock Issued During Period, Shares, Warrants Exercised						498,889
Exercise of warrants							1,428			1,428
Conversion of redeemable convertible preferred stock into common stock (in shares)	(22,638,465)	(10,909,091)	(20,754,461)	(13,202,932)	(52,813,827)	8,651,805
Conversion of redeemable convertible preferred stock into common stock	$ (35,534)	$ (18,065)	$ (29,233)	$ (18,348)	$ (25,656)	$ 9	126,827			126,836
Exercise of investors rights and obligations							1,408			1,408
Stock Issued During Period, Shares, New Issues						7,026,500
Issuance of Common Stock from Initial Public Offering, net of underwriters discounts and issuance costs						$ 7	62,478			$ 62,485
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period						45,413				45,413
Exercise of common stock options							88			$ 88
Stock-based compensation expense							2,164			2,164
Unrealized gain (loss) on short term investments									(5)	(5)
Net loss								(21,377)		(21,377)
Balance (in shares) at Dec. 31, 2015						16,501,500
Balance at Dec. 31, 2015						$ 16	194,651	$ (131,251)	$ (11)	63,405
Issuance of common stock upon ESPP purchase (in shares)						7,632
Issuance of common stock upon ESPP purchase							$ 75			$ 75