Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Accumulated Other Comprehensive Loss	Accumulated Deficit
Beginning balance (in shares) at Dec. 31, 2019		96,189,935
Beginning balance at Dec. 31, 2019	$ 394,890	$ 1,288	$ 818,803	$ 350	$ (425,551)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock in follow-on offering, net of issuance costs of 632 (in shares)		9,000,000
Issuance of common stock in follow-on offering, net of issuance costs of $632	193,948	$ 90	193,858
Issuance of common stock in connection with the Biogen Stock Purchase Agreement (in shares)		13,310,243
Issuance of common stock in connection with the Biogen Stock Purchase Agreement	420,146	$ 133	420,013
Issuances under equity incentive plans (in shares)		1,722,058
Issuances under equity incentive plans	20,655	$ 17	20,638
Vesting of restricted stock units (in shares)		309,097
Vesting of restricted stock units	0	$ 3	(3)
Stock-based compensation	50,351		50,351
Net Income (loss)	71,136				71,136
Other comprehensive loss	(595)			(595)
Ending balance (in shares) at Dec. 31, 2020		120,531,333
Ending balance at Dec. 31, 2020	1,150,531	$ 1,531	1,503,660	(245)	(354,415)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common stock issuance costs		$ 632
Issuances under equity incentive plans (in shares)		1,117,636
Issuances under equity incentive plans	19,348	$ 11	19,337
Vesting of restricted stock units (in shares)		634,336
Vesting of restricted stock units	0	$ 6	(6)
Stock-based compensation	85,247		85,247
Net Income (loss)	(290,581)				(290,581)
Other comprehensive loss	$ (2,254)			(2,254)
Ending balance (in shares) at Dec. 31, 2021	122,283,305	122,283,305
Ending balance at Dec. 31, 2021	$ 962,291	$ 1,548	1,608,238	(2,499)	(644,996)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock in follow-on offering, net of issuance costs of 632 (in shares)		11,933,962
Issuance of common stock in follow-on offering, net of issuance costs of $632	296,215	$ 120	296,095
Issuances under equity incentive plans (in shares)		911,555
Issuances under equity incentive plans	14,455	$ 10	14,445
Vesting of restricted stock units (in shares)		837,096
Vesting of restricted stock units	0	$ 8	(8)
Stock-based compensation	99,847		99,847
Net Income (loss)	(325,991)				(325,991)
Other comprehensive loss	$ (4,387)			(4,387)
Ending balance (in shares) at Dec. 31, 2022	135,965,918	135,965,918
Ending balance at Dec. 31, 2022	$ 1,042,430	$ 1,686	$ 2,018,617	$ (6,886)	$ (970,987)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common stock issuance costs		$ 1,060