Condensed Statements of Convertible Preferred Stock and Stockholders' (Deficit) Equity - USD ($) $ in Thousands	Total	Common Stock [Member]	Additional Paid-in Capital [Member]	Accumulated Deficit [Member]	Convertible Preferred Stock [Member]
Balance, Value at Dec. 31, 2013	$ (54,075)	$ 4	$ 8,377	$ (62,456)
Balance, Value at Dec. 31, 2013					$ 65,586
Balance, Shares at Dec. 31, 2013		4,288,243
Balance, Shares at Dec. 31, 2013					29,186,929
Preferred stock converted to common shares, Value	65,586	$ 13	65,573		$ (65,586)
Preferred stock converted to common shares, Shares		12,554,171			(29,186,929)
Sale of common stock in initial public offering, net of underwriting discounts and commissions and offering expenses, Value	56,247	$ 6	56,241
Sale of common stock in initial public offering, net of underwriting discounts and commissions and offering expenses, Shares		5,750,000
Stock-based compensation expense	809		809
Shares issued upon exercise of stock options, Value	29		29
Shares issued upon exercise of stock options, Shares		46,000
Net loss	(7,028)			(7,028)
Balance, Value at Jun. 30, 2014	61,568	$ 23	131,029	(69,484)
Balance, Shares at Jun. 30, 2014		22,638,414
Balance, Value at Dec. 31, 2014	51,662	$ 23	131,840	(80,201)
Balance, Shares at Dec. 31, 2014		22,802,039
Stock-based compensation expense	1,146		1,146
Shares issued upon exercise of stock options, Value	35		35
Shares issued upon exercise of stock options, Shares		34,880
Net loss	(10,373)			(10,373)
Balance, Value at Jun. 30, 2015	$ 42,470	$ 23	$ 133,021	$ (90,574)
Balance, Shares at Jun. 30, 2015		22,836,919