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, 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 secondary public offering ($3.75 per share and $6.00 per share for the years ended 2017 and 2015), net of expenses of $2,555 and $2,200 for the years ended 2017 and 2015	$ 5	28,131				28,136
Issuance of common stock in connection with secondary public offering (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
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
Exercise of stock options	$ 1	95				96
Exercise of stock options (in shares)	90,509
Issuance of common stock in connection with secondary public offering ($3.75 per share and $6.00 per share for the years ended 2017 and 2015), net of expenses of $2,555 and $2,200 for the years ended 2017 and 2015	$ 10	37,684				37,694
Issuance of common stock in connection with secondary public offering (in shares)	10,733,334
Issuance 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