Summary of Significant Accounting Policies - Narrative (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2022 USD ($) segment	Mar. 31, 2021 USD ($)	Dec. 31, 2021 USD ($)	[1]
Summary Of Significant Accounting Policies [Line Items]
Net loss	$ 32,450	$ 27,544
Accumulated deficit	451,416		$ 418,966
Cash, cash equivalents and marketable securities	329,800
Common stock remaining to be sold under open market sales agreement	$ 127,200
Number of operating business segment | segment	1
Merck | Revenue | Customer Concentration Risk
Summary Of Significant Accounting Policies [Line Items]
Percentage of revenue	100.00%	100.00%

[1] The condensed consolidated balance sheet as of December 31, 2021 has been derived from the audited financial statements as of that date.