Accrued Liabilities and Other Liabilities - Summary (Details) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Payables and Accruals [Abstract]
Accrued clinical expense	$ 30,523	$ 19,221
Accrued manufacturing expense	36,955	13,019
Accrued development expense	7,660	5,439
Accrued compensation and benefits	12,233	13,964
Other accrued expenses	4,626	1,712
Accrued liabilities	$ 91,997	$ 53,355