Statements of Redeemable Convertible Preferred Stock and Stockholders' Equity (Deficit) (USD $) In Thousands, except Share data	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] Convertible Preferred Stock [Member]	Common Stock [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Total
Balance at at Dec. 31, 2011	$ 31,031	$ 15,677	$ 22,446	$ 14,999				$ (72,664)	$ 5	$ (72,659)
Balance at, shares (in Shares) at Dec. 31, 2011	22,638,465	10,909,091	20,754,461	13,202,932		230,607
Accretion of Series A, A-1, B and C redeemable convertible preferred stock to redemption value	1,602	849	2,480	1,202			(110)	(6,023)		(6,133)
Stock-based compensation expense							110			110
Unrealized gain (loss) on short term investments									(4)	(5)
Net loss								(7,970)		(7,970)
Balance at at Dec. 31, 2012	32,633	16,526	24,926	16,201				(86,657)	1	(86,656)
Balance at, shares (in Shares) at Dec. 31, 2012	22,638,465	10,909,091	20,754,461	13,202,932		230,607
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)
Exercise of common stock options							19			19
Exercise of common stock options, shares (in Shares)						9,298
Stock-based compensation expense							155			155
Unrealized gain (loss) on short term investments									(1)	(1)
Net loss								(7,912)		(7,912)
Balance at at Dec. 31, 2013	34,230	17,374	27,401	17,400				(100,514)		(100,514)
Balance at, shares (in Shares) at Dec. 31, 2013	22,638,465	10,909,091	20,754,461	13,202,932		239,905
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
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
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)
Exercise of common stock options							59			59
Exercise of common stock options, shares (in Shares)						31,356				31,356
Stock-based compensation expense							459			459
Unrealized gain (loss) on short term investments									(6)	(6)
Exercise of warrants							1,428			1,428
Exercise of warrants (in Shares)						498,889
Conversion of redeemable convertible preferred stock into common stock	(35,534)	(18,065)	(29,233)	(18,348)	(25,656)	9	126,827			126,836
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
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						7	62,478			62,485
Issuance of Common Stock from Initial Public Offering, net of underwriters discounts and issuance costs (in Shares)						7,026,500
Net loss								(3,342)		(3,342)
Balance at at Dec. 31, 2014						$ 16	$ 192,324	$ (109,874)	$ (6)	$ 82,460
Balance at, shares (in Shares) at Dec. 31, 2014						16,448,455