STATEMENTS OF CONVERTIBLE PREFERRED STOCK AND STOCKHOLDERS' EQUITY (DEFICIT) - USD ($) $ in Thousands	Series A Preferred Stock	Series B Preferred Stock	Series C Preferred Stock	Common Stock	Additional Paid-in Capital	Treasury Stock	Accumulated Deficit	Total
Balance at Dec. 31, 2013	$ 30,596	$ 17,929	$ 21,314
Balance (in shares) at Dec. 31, 2013	18,777,860	12,220,661	18,381,463
Increase (Decrease) in Temporary Equity
Issuance of Series C preferred stock			$ 500
Issuance of Series C preferred stock (in shares)			422,119
Balance at Dec. 31, 2013				$ 1	$ 1,121		$ (61,503)	$ (60,381)
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 and $6.00 per share for the year ended 2014 and 2015), net of expenses of $4,862 and $2,200 for the year ended 2014 and 2015				$ 6	41,196			41,202
Common stock issued (in shares)				5,758,000
Net loss							(10,833)	(10,833)
Balance at Dec. 31, 2014				$ 14	113,476		(72,336)	41,154
Balance (in shares) at Dec. 31, 2014				14,036,985		29,231
Increase (Decrease) in Stockholders' Equity (Deficit)
Stock-based compensation expense					2,108			2,108
Exercise of stock options					373			373
Exercise of stock options (in shares)				327,098
Issuance of common stock in connection with initial public offering ($8.00 per share and $6.00 per share for the year ended 2014 and 2015), net of expenses of $4,862 and $2,200 for the year ended 2014 and 2015				$ 5	28,131			28,136
Common stock issued (in shares)				5,056,003
Net loss							(24,850)	(24,850)
Balance at Dec. 31, 2015				$ 19	144,088		(97,186)	46,921
Balance (in shares) at Dec. 31, 2015				19,420,086		29,231
Increase (Decrease) in Stockholders' Equity (Deficit)
Stock-based compensation expense					3,077			3,077
Exercise of stock options				$ 1	123			124
Exercise of stock options (in shares)				118,365
Issuance of restricted stock (in shares)				195,900
Net loss							(28,643)	(28,643)
Balance at Dec. 31, 2016				$ 20	$ 147,288		$ (125,829)	$ 21,479
Balance (in shares) at Dec. 31, 2016				19,734,351		29,231