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			2,570		$ 2,570
Issuance of common stock upon exercise of stock options (shares)	15,967				15,967
Issuance of common stock upon exercise of stock options, amount			74		$ 74
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				(15,496)	(15,496)
Ending balance (shares) at Jun. 30, 2018	12,947,950	0
Ending balance, amount at Jun. 30, 2018	$ 13	$ 0	358,898	(304,396)	54,515
Beginning balance (shares) at Mar. 31, 2018	12,896,225	0
Beginning balance, amount at Mar. 31, 2018	$ 13	$ 0	357,754	(299,179)	58,588
Share-based compensation			943		$ 943
Issuance of common stock upon exercise of stock options (shares)	750				750
Issuance of common stock upon exercise of stock options, amount			1		$ 1
Cancellation of restricted stock (shares)	(10,000)
Cancellation of restricted stock, amount					0
Issuance of common stock (shares)	60,975
Issuance of common stock, amount			200		200
Net loss				(5,217)	(5,217)
Ending balance (shares) at Jun. 30, 2018	12,947,950	0
Ending balance, amount at Jun. 30, 2018	$ 13	$ 0	358,898	(304,396)	54,515
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			1,111		$ 1,111
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				(10,313)	(10,313)
Ending balance (shares) at Jun. 30, 2019	13,146,831	0
Ending balance, amount at Jun. 30, 2019	$ 13	$ 0	362,737	(338,029)	24,721
Beginning balance (shares) at Mar. 31, 2019	13,116,462	0
Beginning balance, amount at Mar. 31, 2019	$ 13	$ 0	362,076	(333,076)	29,013
Share-based compensation			560		$ 560
Issuance of common stock upon exercise of stock options (shares)	57,036				57,036
Issuance of common stock upon exercise of stock options, amount			101		$ 101
Cancellation of restricted stock (shares)	(26,667)
Cancellation of restricted stock, amount					0
Net loss				(4,953)	(4,953)
Ending balance (shares) at Jun. 30, 2019	13,146,831	0
Ending balance, amount at Jun. 30, 2019	$ 13	$ 0	$ 362,737	$ (338,029)	$ 24,721