Condensed Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Common Stock [Member]	Preferred Stock [Member]	Additional Paid-In Capital [Member]	Accumulated Deficit [Member]	Accumulated Other Comprehensive Loss [Member]
Beginning Balance, Value at Dec. 31, 2020	$ 184,897	$ 10	$ 36,127	$ 1,137,470	$ (988,713)	$ 3
Beginning Balance, Shares at Dec. 31, 2020		101,627,070	337,800,000
Exercise of stock options and vesting of restricted stock units, Value	199			199
Exercise of stock options and vesting of restricted stock units, Shares		188,000
Stock-based compensation	6,943			6,943
Issuance of shares under employee stock purchase plan, Value	1,191			1,191
Issuance of shares under employee stock purchase plan, Shares		146,049
Issuance of shares of common stock in lieu of board fees	72			72
Issuance of shares of common stock in lieu of board fees, Shares		7,632
Unrealized (loss) gain on available-for-sale securities	3					3
Net loss	(70,274)				(70,274)
Ending Balance, Value at Mar. 31, 2021	123,031	$ 10	$ 36,127	1,145,875	(1,058,987)	6
Ending Balance, Shares at Mar. 31, 2021		101,968,751	337,800
Beginning Balance, Value at Dec. 31, 2021	(20,688)	$ 11	$ 36,127	1,183,006	(1,239,835)	3
Beginning Balance, Shares at Dec. 31, 2021		106,097,528	337,800
Issuance of common stock, Value	81,828	$ 6		81,822
Issuance of common stock, Shares		58,139,825
Vesting of restricted stock units		276,761
Stock-based compensation	5,238			5,238
Issuance of shares under employee stock purchase plan, Value	391			391
Issuance of shares under employee stock purchase plan, Shares		308,473
Issuance of shares of common stock in lieu of board fees	51			51
Issuance of shares of common stock in lieu of board fees, Shares		45,109
Unrealized (loss) gain on available-for-sale securities	(194)					(194)
Net loss	(55,505)				(55,505)
Ending Balance, Value at Mar. 31, 2022	$ 11,121	$ 17	$ 36,127	$ 1,270,508	$ (1,295,340)	$ (191)
Ending Balance, Shares at Mar. 31, 2022		164,867,696,000	337,800,000