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, 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)
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
Accretion of Series A, A-1, B, C and D redeemable convertible preferred stock to redemption value	$ 1,304	$ 691	$ 1,832	$ 948	$ 1,578		(335)	(6,018)		(6,353)
Exercise of common stock options (in shares)						31,356
Exercise of common stock options							59			59
Stock-based compensation expense							459			459
Unrealized gain (loss) on short term investments									(6)	(6)
Exercise of warrants (in shares)						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
Issuance of Common Stock from Initial Public Offering, net of underwriters discounts and issuance costs (in shares)						7,026,500
Issuance of Common Stock from Initial Public Offering, net of underwriters discounts and issuance costs						$ 7	62,478			62,485
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
Exercise of common stock options (in shares)						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
Exercise of common stock options (in shares)						97,521				97,521
Exercise of common stock options						$ 1	196			$ 197
Stock-based compensation expense							3,343			3,343
Unrealized gain (loss) on short term investments									11	11
Net loss								(28,526)		(28,526)
Balance (in shares) at Dec. 31, 2016						16,603,559
Balance at Dec. 31, 2016						$ 17	198,201	$ (159,777)		38,441
Issuance of common stock upon ESPP purchase (in shares)						4,538
Issuance of common stock upon ESPP purchase							$ 11			$ 11