CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) $ in Thousands	Common Stock	Additional Paid-in Capital	Treasury Stock	Accumulated Other Comprehensive Loss	Accumulated Deficit	Total
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 (forfeiture) 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
Increase (Decrease) in Stockholders' Equity (Deficit)
Stock-based compensation expense		2,880				2,880
Issuance of common stock under equity distribution agreement, net of expenses of $380	$ 10	14,843				14,853
Issuance of common stock under equity distribution agreement (in shares)	9,768,142
Issuance of common stock in connection with secondary public offering ($3.75 per share for the years ended 2018 and 2017, respectively), net of expenses of $2,853 and $2,555 for the years ended 2018 and 2017, respectively	$ 10	37,684				37,694
Issuance of common stock in connection with secondary public offering (in shares)	10,733,334
Exercise of stock options	$ 1	95				96
Exercise of stock options (in shares)	90,509
Issuance (forfeiture) of restricted stock (in shares)	223,600
Net loss					(18,898)	(18,898)
Unrealized loss on investments				$ (96)		(96)
Balance at Dec. 31, 2017	$ 41	202,790		(96)	(144,727)	58,008
Balance (in shares) at Dec. 31, 2017	40,549,936		29,231
Increase (Decrease) in Stockholders' Equity (Deficit)
Stock-based compensation expense		4,788				4,788
Issuance of common stock in connection with secondary public offering ($3.75 per share for the years ended 2018 and 2017, respectively), net of expenses of $2,853 and $2,555 for the years ended 2018 and 2017, respectively	$ 12	42,135				42,147
Issuance of common stock in connection with secondary public offering (in shares)	12,000,000
Exercise of stock options		14				14
Exercise of stock options (in shares)	12,308
Issuance (forfeiture) of restricted stock (in shares)	(14,000)
Net loss					(36,726)	(36,726)
Unrealized loss on investments				94		94
Balance at Dec. 31, 2018	$ 53	$ 249,727		$ (2)	$ (181,453)	$ 68,325
Balance (in shares) at Dec. 31, 2018	52,548,244		29,231