Condensed Consolidated Statements of Equity - USD ($) $ in Thousands	Common Stock [Member]	Additional Paid-in Capital [Member]	Treasury Stock [Member]	Accumulated Deficit [Member]	Total
Balance at Dec. 31, 2018	$ 84	$ 552,531	$ (234)	$ (528,345)	$ 24,036
Balance (in shares) at Dec. 31, 2018	83,911,855		41,309
Issuance of restricted stock (in shares)	23,000
Warrants issued with debt financing		993			993
Forfeiture of restricted stock (in shares)	(67,628)
Issuance of common stock in At-the-Market offerings (net of offering costs)	$ 5	27,494			27,499
Issuance of common stock in At-the-Market offerings (net of offering costs) (in shares)	4,715,000
Compensation in respect of restricted stock granted to employees, directors and consultants		1,882			1,882
Net loss				(35,156)	(35,156)
Balance at Mar. 31, 2019	$ 89	582,900	$ (234)	(563,501)	19,254
Balance (in shares) at Mar. 31, 2019	88,582,227		41,309
Balance at Dec. 31, 2018	$ 84	552,531	$ (234)	(528,345)	24,036
Balance (in shares) at Dec. 31, 2018	83,911,855		41,309
Net loss					(133,299)
Balance at Sep. 30, 2019	$ 97	635,989	$ (234)	(661,643)	(25,791)
Balance (in shares) at Sep. 30, 2019	96,670,197		41,309
Balance at Mar. 31, 2019	$ 89	582,900	$ (234)	(563,501)	19,254
Balance (in shares) at Mar. 31, 2019	88,582,227		41,309
Issuance of restricted stock	$ 1	(1)
Issuance of restricted stock (in shares)	1,245,080
Forfeiture of restricted stock (in shares)	(38,418)
Issuance of common stock (net of offering costs)		11			11
Issuance of common stock in At-the-Market offerings (net of offering costs)	$ 3	28,392			28,395
Issuance of common stock in At-the-Market offerings (net of offering costs) (in shares)	3,616,359
Compensation in respect of restricted stock granted to employees, directors and consultants		1,757			1,757
Net loss				(36,212)	(36,212)
Balance at Jun. 30, 2019	$ 93	613,059	$ (234)	(599,713)	13,205
Balance (in shares) at Jun. 30, 2019	93,405,248		41,309
Issuance of restricted stock (in shares)	318,440
Forfeiture of restricted stock (in shares)	(5,334)
Issuance of common stock in At-the-Market offerings (net of offering costs)	$ 4	20,755			20,759
Issuance of common stock in At-the-Market offerings (net of offering costs) (in shares)	2,943,460
Compensation in respect of restricted stock granted to employees, directors and consultants		2,075			2,075
Shares issued in connection with in-licensing agreements		100			100
Shares issued in connection with in-licensing agreements (in shares)	8,383
Net loss				(61,930)	(61,930)
Balance at Sep. 30, 2019	$ 97	635,989	$ (234)	(661,643)	(25,791)
Balance (in shares) at Sep. 30, 2019	96,670,197		41,309
Balance at Dec. 31, 2019	$ 109	739,956	$ (234)	(701,216)	38,615
Balance (in shares) at Dec. 31, 2019	109,425,243		41,309
Issuance of restricted stock	$ 1	(1)
Issuance of restricted stock (in shares)	774,300
Forfeiture of restricted stock (in shares)	(10,000)
Issuance of common stock in connection with exercise of options		80			80
Issuance of common stock in connection with exercise of options	19,750
Compensation in respect of restricted stock granted to employees, directors and consultants		11,068			11,068
Net loss				(51,116)	(51,116)
Balance at Mar. 31, 2020	$ 110	751,103	$ (234)	(752,332)	(1,353)
Balance (in shares) at Mar. 31, 2020	110,209,293		41,309
Balance at Dec. 31, 2019	$ 109	739,956	$ (234)	(701,216)	38,615
Balance (in shares) at Dec. 31, 2019	109,425,243		41,309
Net loss					(191,163)
Balance at Sep. 30, 2020	$ 129	1,063,142	$ (234)	(892,379)	170,658
Balance (in shares) at Sep. 30, 2020	128,959,861		41,309
Balance at Mar. 31, 2020	$ 110	751,103	$ (234)	(752,332)	(1,353)
Balance (in shares) at Mar. 31, 2020	110,209,293		41,309
Issuance of restricted stock	$ 2	(2)
Issuance of restricted stock (in shares)	2,208,529
Forfeiture of restricted stock (in shares)	(41,666)
Issuance of common stock (net of offering costs)	$ 10	165,032			165,042
Issuance of common stock (net of offering costs) (in shares)	9,775,000
Issuance of common stock in connection with exercise of options		16			16
Issuance of common stock in connection with exercise of options	3,750
Issuance of common stock in At-the-Market offerings (net of offering costs)	$ 5	76,031			76,036
Issuance of common stock in At-the-Market offerings (net of offering costs) (in shares)	4,535,608
Compensation in respect of restricted stock granted to employees, directors and consultants		7,370			7,370
Net loss				(52,884)	(52,884)
Balance at Jun. 30, 2020	$ 127	999,550	$ (234)	(805,216)	194,227
Balance (in shares) at Jun. 30, 2020	126,690,514		41,309
Issuance of restricted stock	$ 1	(1)
Issuance of restricted stock (in shares)	915,000
Forfeiture of restricted stock (in shares)	(65,000)
Issuance of common stock (net of offering costs)		(1)			(1)
Issuance of common stock in connection with exercise of options		38			38
Issuance of common stock in connection with exercise of options	9,347
Issuance of common stock in At-the-Market offerings (net of offering costs)	$ 1	35,226			35,227
Issuance of common stock in At-the-Market offerings (net of offering costs) (in shares)	1,410,000
Compensation in respect of restricted stock granted to employees, directors and consultants		28,330			28,330
Net loss				(87,163)	(87,163)
Balance at Sep. 30, 2020	$ 129	$ 1,063,142	$ (234)	$ (892,379)	$ 170,658
Balance (in shares) at Sep. 30, 2020	128,959,861		41,309