CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY (DEFICIT) - USD ($) $ in Thousands	Common Stock	Treasury Stock	Additional Paid-in Capital	Accumulated Deficit	Accumulated Other Comprehensive (Loss) Income	Total
Balance, beginning at Dec. 31, 2015	$ 16	$ (171)	$ 195,314	$ (116,785)		$ 78,374
Balance, beginning (in shares) at Dec. 31, 2015	16,025,155	(9,197)
Increase (Decrease) in Stockholders Equity
Proceeds from exercise of options and warrants			13			13
Proceeds from exercise of options and warrants (in shares)	54,747
Purchase of treasury stock		$ (61)				(61)
Purchase of treasury stock (in shares)		(9,709)
Share-based compensation expense			3,460			3,460
Net unrealized loss on investments					$ (1)	(1)
Net loss				(82,751)		(82,751)
Balance, ending at Dec. 31, 2016	$ 16	$ (232)	198,787	(199,536)	(1)	(966)
Balance, ending (in shares) at Dec. 31, 2016	16,079,902	18,906
Increase (Decrease) in Stockholders Equity
Issuance of common stock, net of issuance costs	$ 12		64,548			64,560
Issuance of common stock, net of issuance costs (in shares)	12,019,639
Issuance of common stock upon conversion of convertible notes	$ 1		6,585			6,586
Issuance of common stock upon conversion of convertible notes (in shares)	929,967
Purchase of treasury stock		$ (120)				(120)
Purchase of treasury stock (in shares)		(14,895)
Share-based compensation expense			4,051			4,051
Recognition of beneficial conversion feature on convertible notes			613			613
Conversion of Redeemable Preferred Stock (in shares)	1,249
Net unrealized loss on investments					(5)	(5)
Net loss				(65,772)		(65,772)
Balance, ending at Dec. 31, 2017	$ 29	$ (352)	274,584	(265,308)	(6)	8,947
Balance, ending (in shares) at Dec. 31, 2017	29,030,757	(33,801)
Increase (Decrease) in Stockholders Equity
Issuance of common stock, net of issuance costs	$ 21		47,271			47,292
Issuance of common stock, net of issuance costs (in shares)	20,651,524
Issuance of common stock upon RSU conversion (in shares)	26,991
Shares issued from exercise of stock options (in shares)	832
Payroll tax withheld for release of RSUs			(46)			(46)
Share-based compensation expense			3,321			3,321
Net unrealized loss on investments					$ 6	6
Net loss				(51,675)		(51,675)
Balance, ending at Dec. 31, 2018	$ 50	$ (352)	$ 325,130	$ (316,983)		$ 7,845
Balance, ending (in shares) at Dec. 31, 2018	49,710,104	33,801