CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) $ in Thousands	Common Stock	Preferred Stock	Additional Paid-In Capital	Accumulated Deficit	Total
Beginning balance (shares) at Dec. 31, 2017	13,059,341	0
Beginning balance, amount at Dec. 31, 2017	$ 13	$ 0	$ 356,054	$ (288,900)	$ 67,167
Share-based compensation			4,366		$ 4,366
Issuance of common stock upon exercise of stock options (shares)	16,967				16,967
Issuance of common stock upon exercise of stock options, amount			78		$ 78
Cancellation of restricted stock (shares)	(188,333)
Cancellation of restricted stock, amount					0
Issuance of common stock (shares)	60,975
Issuance of common stock, amount			200		200
Net loss				(33,531)	(33,531)
Ending balance (shares) at Sep. 30, 2018	12,948,950	0
Ending balance, amount at Sep. 30, 2018	$ 13	$ 0	360,699	(322,432)	38,280
Beginning balance (shares) at Jun. 30, 2018	12,947,950	0
Beginning balance, amount at Jun. 30, 2018	$ 13	$ 0	358,898	(304,396)	54,515
Share-based compensation			1,797		$ 1,797
Issuance of common stock upon exercise of stock options (shares)	1,000				1,000
Issuance of common stock upon exercise of stock options, amount			4		$ 4
Net loss				(18,036)	(18,036)
Ending balance (shares) at Sep. 30, 2018	12,948,950	0
Ending balance, amount at Sep. 30, 2018	$ 13	$ 0	360,699	(322,432)	38,280
Beginning balance (shares) at Dec. 31, 2018	12,960,450	0
Beginning balance, amount at Dec. 31, 2018	$ 13	$ 0	361,218	(327,716)	33,515
Share-based compensation			1,762		$ 1,762
Issuance of common stock upon exercise of stock options (shares)	213,048				213,048
Issuance of common stock upon exercise of stock options, amount			408		$ 408
Cancellation of restricted stock (shares)	(26,667)
Cancellation of restricted stock, amount					0
Net loss				(12,052)	(12,052)
Ending balance (shares) at Sep. 30, 2019	13,146,831	0
Ending balance, amount at Sep. 30, 2019	$ 13	$ 0	363,388	(339,768)	23,633
Beginning balance (shares) at Jun. 30, 2019	13,146,831	0
Beginning balance, amount at Jun. 30, 2019	$ 13	$ 0	362,737	(338,029)	24,721
Share-based compensation			651		$ 651
Issuance of common stock upon exercise of stock options (shares)					0
Net loss				(1,739)	$ (1,739)
Ending balance (shares) at Sep. 30, 2019	13,146,831	0
Ending balance, amount at Sep. 30, 2019	$ 13	$ 0	$ 363,388	$ (339,768)	$ 23,633