Accrued Liabilities and Other Liabilities - Summary (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Payables and Accruals [Abstract]
Accrued clinical expense	$ 18,956	$ 19,221
Accrued manufacturing expense	27,988	13,019
Accrued development expense	9,103	5,439
Accrued compensation and benefits	16,763	13,964
Other accrued expenses	6,346	1,712
Accrued liabilities	$ 79,156	$ 53,355