Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Public Offering	Common Stock	Common Stock Public Offering	Common Stock At-the-market Sales Agreement	Additional Paid-In  Capital	Additional Paid-In  Capital Public Offering	Additional Paid-In  Capital At-the-market Sales Agreement	Accumulated Other Comprehensive Loss	Accumulated Deficit
Beginning Balance, (in shares) at Dec. 31, 2019			113,299,612
Beginning Balance at Dec. 31, 2019	$ 190,393		$ 113			$ 918,205			$ (3,498)	$ (724,427)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net loss	(160,868)									(160,868)
Other comprehensive (loss) income	1,669								1,669
Recognition of stock-based compensation expense	$ 17,554					17,554
Issuance of common shares under an at-the-market sales agreement (in shares)	3,950,398			24,916,667	3,950,398
Issuance of common shares under an at-the-market sales agreement	$ 14,902	$ 69,665		$ 25	$ 4		$ 69,640	$ 14,898
Issuance of common stock to 401(k) plan for employees, (in shares)			96,959
Issuance of common stock to 401(k) plan for employees	265					265
Issuance of common stock for employee stock purchase plan (in shares)			225,310
Issuance of common stock for employee stock purchase plan	$ 650					650
Issuance of common stock upon exercise of stock options (in shares)	3,542		3,542
Issuance of common stock upon exercise of stock options	$ 13					13
Restricted stock award grants, net of forfeitures (in shares)			3,589,761
Restricted stock award grants, net of forfeitures	$ 0		$ 4			(4)
Issuance of common stock upon vesting of restricted stock units (in shares)			861
Ending Balance, (in shares) at Dec. 31, 2020	146,083,110		146,083,110
Ending Balance at Dec. 31, 2020	$ 134,243		$ 146			1,021,221			(1,829)	(885,295)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net loss	(158,628)									(158,628)
Other comprehensive (loss) income	(1,213)								(1,213)
Recognition of stock-based compensation expense	$ 19,839					19,839
Issuance of common shares under an at-the-market sales agreement (in shares)	15,851,391				15,851,391
Issuance of common shares under an at-the-market sales agreement	$ 52,621				$ 16			$ 52,605
Issuance of common stock for employee stock purchase plan (in shares)			358,007
Issuance of common stock for employee stock purchase plan	$ 685		$ 1			684
Issuance of common stock upon exercise of stock options (in shares)	1,250		1,250
Issuance of common stock upon exercise of stock options	$ 4					4
Restricted stock award grants, net of forfeitures (in shares)			2,206,869
Restricted stock award grants, net of forfeitures	$ 2		$ 2
Issuance of common stock upon vesting of restricted stock units (in shares)			1,386
Ending Balance, (in shares) at Dec. 31, 2021	164,502,013		164,502,013
Ending Balance at Dec. 31, 2021	$ 47,553		$ 165			$ 1,094,353			$ (3,042)	$ (1,043,923)