STATEMENTS OF CONVERTIBLE PREFERRED STOCK AND STOCKHOLDERS' EQUITY (DEFICIT) (USD $) In Thousands, except Share data, unless otherwise specified	Series A Preferred Stock USD ($)	Series B Preferred Stock USD ($)	Series C Preferred Stock USD ($)	Common Stock USD ($)	Additional Paid-in Capital USD ($)	Treasury Stock	Accumulated Deficit USD ($)	Total USD ($)
Balance at Dec. 31, 2012	$ 30,596	$ 17,929	$ 11,023
Balance at Dec. 31, 2012				1	867		(56,233)	(55,365)
Balance (in shares) at Dec. 31, 2012	18,777,860	12,220,661	9,654,443
Balance (in shares) at Dec. 31, 2012				478,745		29,231
Increase (Decrease) in Stockholders' Equity (Deficit)
Stock-based compensation expense					236			236
Exercise of stock options					18			18
Exercise of stock options (in shares)				15,515
Net loss							(5,270)	(5,270)
Increase (Decrease) in Temporary Equity
Issuance of Series C preferred stock			10,291
Issuance of Series C preferred stock (in shares)			8,727,020
Balance at Dec. 31, 2013	30,596	17,929	21,314
Balance at Dec. 31, 2013				1	1,121		(61,503)	(60,381)
Balance (in shares) at Dec. 31, 2013	18,777,860	12,220,661	18,381,463
Balance (in shares) at Dec. 31, 2013				494,260		29,231
Increase (Decrease) in Stockholders' Equity (Deficit)
Stock-based compensation expense					698			698
Exercise of stock options					128			128
Exercise of stock options (in shares)				122,634
Conversion of convertible preferred stock to common stock	(30,596)	(17,929)	(21,814)	7	70,333			70,340
Conversion of convertible preferred stock to common stock (in shares)	(18,777,860)	(12,220,661)	(18,803,582)	7,661,871
Exercise and conversion of convertible preferred stock warrants into common stock (in shares)				220
Issuance of common stock in connection with initial public offering ($8.00 per share), net of expenses of $4,862				6	41,196			41,202
Common stock issued (in shares)				5,758,000
Net loss							(10,833)	(10,833)
Increase (Decrease) in Temporary Equity
Issuance of Series C preferred stock			500
Issuance of Series C preferred stock (in shares)			422,119
Common stock issued upon conversion of warrants (in shares)				220
Balance at Dec. 31, 2014				$ 14	$ 113,476		$ (72,336)	$ 41,154
Balance (in shares) at Dec. 31, 2014				14,036,985		29,231