Condensed Consolidated Statements of Stockholders' Equity (Unaudited) - USD ($) shares in Thousands, $ in Thousands	Total	Equity-classified awards	Common Shares	Additional Paid-in Capital	Additional Paid-in Capital Equity-classified awards	Accumulated Deficit
Beginning Balance at Dec. 31, 2019	$ 14,846		$ 16	$ 600,451		$ (585,621)
Beginning Balance (in shares) at Dec. 31, 2019			16,081
Stock-based compensation expense related to equity- classified awards		$ 543			$ 543
Net loss	(8,381)					(8,381)
Ending Balance at Mar. 31, 2020	7,008		$ 16	600,994		(594,002)
Ending Balance (in shares) at Mar. 31, 2020			16,081
Beginning Balance at Dec. 31, 2020	35,294		$ 27	656,472		(621,205)
Beginning Balance (in shares) at Dec. 31, 2020			26,883
Issuance of common stock in a public offering (net of issuance costs of $3.6 million)	51,603		$ 7	51,596
Issuance of common stock in a public offering, excluding to related parties, net (in shares)			6,900
Issuance of common stock from the SVB Leerink sales agreement (net of issuance costs of $0.1 million)	3,377			3,377
Issuance of common stock from the SVB Leerink sales agreement (in shares)			331
Issuance of common stock in connection with warrant exercises	3,092			3,092
Issuance of common stock in connection with warrant exercises (in shares)			247
Stock-based compensation expense related to equity- classified awards		$ 1,204			$ 1,204
Net loss	(22,122)					(22,122)
Ending Balance at Mar. 31, 2021	$ 72,448		$ 34	$ 715,741		$ (643,327)
Ending Balance (in shares) at Mar. 31, 2021			34,361