Consolidated Statements of Equity - USD ($) $ in Thousands	Common Stock [Member]	Contingently Issuable Share [Member]	Additional Paid-in Capital [Member]	Treasury Stock [Member]	Accumulated Deficit [Member]	Total
Balance at Dec. 31, 2015	$ 54		$ 259,887	$ (234)	$ (158,134)	$ 101,573
Balance (in shares) at Dec. 31, 2015	54,095,110	6		41,309
Issuance of common stock in connection with exercise of warrants			618			618
Issuance of common stock in connection with exercise of warrants (in shares)	273,370
Issuance of common stock in connection with conversion of notes payable			33			33
Issuance of common stock in connection with conversion of notes payable (in shares)	3,710
Issuance of restricted stock	$ 2		(2)
Issuance of restricted stock (in shares)	1,924,639
Forfeiture of restricted stock (in shares)	(46,773)
Issuance of common stock in At-the-Market offering (net of offering costs)			4,386			4,386
Issuance of common stock in At-the-Market offering (net of offering costs) (in shares)	570,366
Compensation in respect of restricted stock granted to employees, directors and consultants			7,510			7,510
Adjustment to contingently issuable shares		$ (6)
Net loss					(78,253)	(78,253)
Balance at Dec. 31, 2016	$ 57		272,432	$ (234)	(236,387)	35,868
Balance (in shares) at Dec. 31, 2016	56,820,422	0		41,309
Issuance of common stock in connection with exercise of warrants			2,142			2,143
Issuance of common stock in connection with exercise of warrants (in shares)	887,585
Issuance of restricted stock	$ 2		(2)
Issuance of restricted stock (in shares)	1,836,511
Forfeiture of restricted stock (in shares)	(53,875)
Issuance of common stock in public offering (net of offering costs of $3.6 million)	$ 6		53,634			53,640
Issuance of common stock in public offering (net of offering costs of $3.6 million) (in shares)	5,897,436
Issuance of common stock in At-the-Market offering (net of offering costs)	$ 8		77,865			77,873
Issuance of common stock in At-the-Market offering (net of offering costs) (in shares)	7,793,671
Compensation in respect of restricted stock granted to employees, directors and consultants			15,945			15,945
Net loss					(118,476)	(118,476)
Balance at Dec. 31, 2017	$ 73		422,017	$ (234)	(354,863)	66,993
Balance (in shares) at Dec. 31, 2017	73,181,750	0		41,309
Issuance of restricted stock	$ 2		(2)
Issuance of restricted stock (in shares)	1,562,211
Forfeiture of restricted stock (in shares)	(191,196)
Issuance of common stock in At-the-Market offering (net of offering costs)	$ 9		113,630			113,639
Issuance of common stock in At-the-Market offering (net of offering costs) (in shares)	9,025,222
Compensation in respect of restricted stock granted to employees, directors and consultants			12,886			12,886
Shares issued in connection with in-licensing agreements			4,000			4,000
Shares issued in connection with in-licensing agreements (in shares)	333,868
Net loss					(173,482)	(173,482)
Balance at Dec. 31, 2018	$ 84		$ 552,531	$ (234)	$ (528,345)	$ 24,036
Balance (in shares) at Dec. 31, 2018	83,911,855	0		41,309