Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-In Capital	Unrealized Gain/Loss	Accumulated Deficit
Beginning balance (in shares) at Dec. 31, 2018		116,887,518
Beginning balance at Dec. 31, 2018	$ 635,928	$ 1	$ 1,150,583	$ (261)	$ (514,395)
Issuance of common stock, net of issuance costs (in shares)		4,068,912
Issuance of common stock, net of issuance costs	25,785		25,785
Proceeds from sale of stock under employee stock purchase plan (in shares)		87,530
Proceeds from sale of stock under employee stock purchase plan	383		383
Exercise of options (in shares)		362,796
Exercise of options	560		560
Share-based compensation expense	11,925		11,925
Restricted stock unit vesting (in shares)		323,136
Retired shares (in shares)		(55,324)
Retired shares	(426)		(426)
Unrealized gain	261			261
Net loss	(279,659)				(279,659)
Ending balance (in shares) at Dec. 31, 2019		121,674,568
Ending balance at Dec. 31, 2019	394,757	$ 1	1,188,810	0	(794,054)
Issuance of common stock, net of issuance costs (in shares)		24,133,348
Issuance of common stock, net of issuance costs	209,519		209,519
Proceeds from sale of stock under employee stock purchase plan (in shares)		235,658
Proceeds from sale of stock under employee stock purchase plan	1,100		1,100
Exercise of options (in shares)		166,633
Exercise of options	1,226		1,226
Share-based compensation expense	24,460		24,460
Restricted stock unit vesting (in shares)		1,863,878
Unrealized gain	13			13
Net loss	$ (383,457)				(383,457)
Ending balance (in shares) at Dec. 31, 2020	148,074,085	148,074,085
Ending balance at Dec. 31, 2020	$ 247,618	$ 1	1,425,115	13	(1,177,511)
Issuance of common stock, net of issuance costs (in shares)		26,352,343
Issuance of common stock, net of issuance costs	88,204		88,204
Proceeds from sale of stock under employee stock purchase plan (in shares)		307,193
Proceeds from sale of stock under employee stock purchase plan	$ 746		746
Exercise of options (in shares)	0
Share-based compensation expense	$ 22,735		22,735
Restricted stock unit vesting (in shares)		2,267,342
Unrealized gain	(7)			(7)
Net loss	$ (282,840)				(282,840)
Ending balance (in shares) at Dec. 31, 2021	177,000,963	177,000,963
Ending balance at Dec. 31, 2021	$ 76,456	$ 1	$ 1,536,800	$ 6	$ (1,460,351)