Condensed Consolidated Statements of Stockholders’ Equity - USD ($) shares in Thousands, $ in Thousands	Total	Public Offering	Private Placement	Common Shares	Common Shares Public Offering	Common Shares Private Placement	Additional Paid-in Capital	Additional Paid-in Capital Public Offering	Additional Paid-in Capital Private Placement	Accumulated Other Comprehensive Income	Accumulated Deficit
Beginning balance (in shares) at Dec. 31, 2020				26,883
Beginning balance at Dec. 31, 2020	$ 35,294			$ 27			$ 656,472			$ 0	$ (621,205)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock (in shares)					6,900	331
Issuance of common stock		$ 51,603	$ 3,377		$ 7			$ 51,596	$ 3,377
Issuance of common stock in connection with warrant exercises (in shares)				247
Issuance of common stock in connection with warrant exercises	3,092						3,092
Stock-based compensation expense related to equity-classified awards	1,204						1,204
Unrealized gain on available-for-sale securities	0
Net loss	(22,122)										(22,122)
Ending balance (in shares) at Mar. 31, 2021				34,361
Ending balance at Mar. 31, 2021	72,448			$ 34			715,741			0	(643,327)
Beginning balance (in shares) at Dec. 31, 2021				34,475
Beginning balance at Dec. 31, 2021	45,870			$ 34			720,386			(3)	(674,547)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock-based compensation expense related to equity-classified awards	1,267						1,267
Unrealized gain on available-for-sale securities	4									4
Net loss	(10,199)										(10,199)
Ending balance (in shares) at Mar. 31, 2022				34,475
Ending balance at Mar. 31, 2022	$ 36,942			$ 34			$ 721,653			$ 1	$ (684,746)