Consolidated Statements of Stockholders' Equity - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock	Preferred Stock	Treasury Stock	Additional Paid-in Capital	Accumulated Deficit	Accumulated Other Comprehensive (Loss) Income	2020 Financing	2020 Financing Common Stock	2020 Financing Preferred Stock	2020 Financing Additional Paid-in Capital
Beginning balance (in shares) at Dec. 31, 2018		16,642		0
Beginning balance at Dec. 31, 2018	$ 168,521	$ 17		$ 0	$ 676,572	$ (509,406)	$ 1,338
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock-based compensation	2,981				2,981
Exercise of stock options and warrants (in shares)		12
Exchange of shares for Series B Warrants	236				236
Award of restricted stock units (in shares)		47
Award of restricted stock units	1				1
Return of common stock to pay withholding taxes on restricted stock (in shares)				15
Return of common stock to pay withholding taxes on restricted stock	(499)				(499)
Cancellation of treasury stock (in shares)				(15)
Cumulative effect of change in accounting principle	0				(7)	7
Other comprehensive (loss) income	(1,949)						(1,949)
Net loss	(22,525)					(22,525)
Ending balance (in shares) at Mar. 31, 2019		16,701		0
Ending balance at Mar. 31, 2019	146,766	$ 17		$ 0	679,284	(531,924)	(611)
Beginning balance (in shares) at Dec. 31, 2019		20,691	0	0
Beginning balance at Dec. 31, 2019	55,535	$ 21	$ 0	$ 0	720,484	(663,600)	(1,370)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock-based compensation	1,923				1,923
Issuance of common and preferred stock, net of issuance costs (in shares)		7,030							14,122	7,937
Issuance of common stock, net of issuance costs	11,212	$ 7			11,205			$ 13,525	$ 14	$ 79	$ 13,432
Conversion of preferred stock to common stock (in shares)		3,053	3,053
Conversion of preferred stock to common stock	0	$ 3	$ 30		27
Exercise of stock options and warrants (in shares)		2,041
Exchange of shares for Series B Warrants	2,470	$ 2			2,468
Award of restricted stock units (in shares)		141
Award of restricted stock units	0
Return of common stock to pay withholding taxes on restricted stock (in shares)				28
Return of common stock to pay withholding taxes on restricted stock	(33)				(33)
Cancellation of treasury stock (in shares)				(28)
Other comprehensive (loss) income	(872)						(872)
Net loss	(16,598)					(16,598)
Ending balance (in shares) at Mar. 31, 2020		47,078	4,884	0
Ending balance at Mar. 31, 2020	$ 67,162	$ 47	$ 49	$ 0	$ 749,506	$ (680,198)	$ (2,242)