Property and Equipment, Net - Schedule of Property and Equipment, Net (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Property Plant And Equipment [Line Items]
Property and equipment, at cost	$ 54,003	$ 51,126
Less: accumulated depreciation and amortization	(14,319)	(8,410)
Property and equipment, net	39,684	42,716
Laboratory Equipment
Property Plant And Equipment [Line Items]
Property and equipment, at cost	11,991	10,837
Manufacturing Equipment
Property Plant And Equipment [Line Items]
Property and equipment, at cost	7,754	4,911
Computers and Purchased Software
Property Plant And Equipment [Line Items]
Property and equipment, at cost	1,596	640
Furniture and Fixtures
Property Plant And Equipment [Line Items]
Property and equipment, at cost	1,363	1,363
Leasehold Improvements
Property Plant And Equipment [Line Items]
Property and equipment, at cost	29,960	30,862
Assets Not Yet in Service
Property Plant And Equipment [Line Items]
Property and equipment, at cost	$ 1,339	$ 2,513