Condensed Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Series A Convertible Voting Preferred Stock [Member]	Common Stock [Member]	Additional Paid-In Capital [Member]	Accumulated Deficit [Member]
Stockholders Equity, Ending Balance at Dec. 31, 2018	$ 94,479		$ 74	$ 771,817	$ (677,412)
Stockholders Equity, Ending Balance, Shares at Dec. 31, 2018			1,859,120
Issuance of common stock for exercise of stock options	445			445
Issuance of common stock for exercise of stock options, Shares			8,056
Stock-based compensation	1,699			1,699
Net loss	(13,032)				(13,032)
Stockholders Equity, Ending Balance at Mar. 31, 2019	83,591		$ 74	773,961	(690,444)
Stockholders Equity, Ending Balance, Shares at Mar. 31, 2019			1,867,176
Stockholders Equity, Ending Balance at Dec. 31, 2019	86,345	$ 1	$ 74	851,957	(765,687)
Stockholders Equity, Ending Balance, Shares at Dec. 31, 2019		103,000	1,867,176
Conversion of Series A convertible voting preferred stock to common stock		$ (1)	$ 8	(7)
Conversion of Series A convertible voting preferred stock to common stock, Shares		(103,000)	7,803,273
Reclassification of warrant liabilities to equity	62,175			62,175
Issuance of common stock in connection with an amendment to the asset purchase agreement, Shares			725,283
Issuance of common stock in connection with an amendment to the asset purchase agreement	8,782		$ 1	8,781
Issuance of warrant in connection with an amendment to the asset purchase agreement	3,188			3,188
Stock-based compensation	918			918
Reverse stock split adjustment			(73)	73
Net loss	(31,912)				(31,912)
Stockholders Equity, Ending Balance at Mar. 31, 2020	$ 129,496		$ 10	$ 927,085	$ (797,599)
Stockholders Equity, Ending Balance, Shares at Mar. 31, 2020			10,395,732