STATEMENTS OF CHANGES IN STOCKHOLDERS' EQUITY - USD ($) $ in Thousands	Total	Common Stock	Additional Paid In Capital	Accumulated Deficit
Balance at Dec. 31, 2018	$ 85,564	$ 161	$ 651,732	$ (566,329)
Balance (in shares) at Dec. 31, 2018		161,066,136
Stock-based compensation	4,741		4,741
Exercise of employee stock options	1,020		1,020
Exercise of employee stock options (in shares)		352,652
Restricted stock awards	1,000	$ 1	999
Restricted stock awards (in shares)		1,408,536
Issuance of common stock upon exercise of warrants, net	52,499	$ 18	52,481
Issuance of common stock upon exercise of warrants, net (in shares)		17,803,031
Issuance of inducement warrants	60,751		60,751
Cancelled restricted common stock (in shares)		(74,599)
Restricted stock buy-back at vesting to cover taxes	(370)		(370)
Restricted stock buy-back at vesting to cover taxes (in shares)		(165,178)
Issuance of common stock in connection with at the market offering, net	2,971	$ 1	2,970
Issuance of common stock in connection with at the market offering, net (in shares)		639,442
Net loss	(102,050)			(102,050)
Balance at Sep. 30, 2019	106,126	$ 181	774,324	(668,379)
Balance (in shares) at Sep. 30, 2019		181,030,020
Balance at Jun. 30, 2019	61,995	$ 162	656,216	(594,383)
Balance (in shares) at Jun. 30, 2019		162,477,963
Stock-based compensation	1,486		1,486
Exercise of employee stock options	420		420
Exercise of employee stock options (in shares)		94,584
Restricted stock awards (in shares)		15,000
Issuance of common stock upon exercise of warrants, net	52,499	$ 18	52,481
Issuance of common stock upon exercise of warrants, net (in shares)		17,803,031
Issuance of inducement warrants	60,751		60,751
Issuance of common stock in connection with at the market offering, net	2,971	$ 1	2,970
Issuance of common stock in connection with at the market offering, net (in shares)		639,442
Net loss	(73,996)			(73,996)
Balance at Sep. 30, 2019	106,126	$ 181	774,324	(668,379)
Balance (in shares) at Sep. 30, 2019		181,030,020
Balance at Dec. 31, 2019	95,010	$ 182	778,953	(684,125)
Balance (in shares) at Dec. 31, 2019		181,803,320
Stock-based compensation	5,393		5,393
Exercise of employee stock options	$ 43		43
Exercise of employee stock options (in shares)	22,916	22,916
Restricted stock awards		$ 1	(1)
Restricted stock awards (in shares)		555,900
Cancelled restricted common stock (in shares)		(141,230)
Issuance of common stock in connection with a public offering, net	$ 88,661	$ 29	88,632
Issuance of common stock in connection with a public offering, net (in shares)		29,110,111
Issuance of common stock in connection with at the market offering, net	13,015	$ 2	13,013
Issuance of common stock in connection with at the market offering, net (in shares)		2,814,673
Net loss	(57,204)			(57,204)
Balance at Sep. 30, 2020	144,918	$ 214	886,033	(741,329)
Balance (in shares) at Sep. 30, 2020		214,165,690
Balance at Jun. 30, 2020	163,414	$ 214	884,214	(721,014)
Balance (in shares) at Jun. 30, 2020		214,150,940
Stock-based compensation	1,792		1,792
Exercise of employee stock options	27		27
Exercise of employee stock options (in shares)		14,750
Net loss	(20,315)			(20,315)
Balance at Sep. 30, 2020	$ 144,918	$ 214	$ 886,033	$ (741,329)
Balance (in shares) at Sep. 30, 2020		214,165,690