Property and Equipment - Schedule of Property and Equipment, Net (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Property Plant And Equipment [Line Items]
Property and equipment, at cost	$ 37,745	$ 4,052
Less accumulated depreciation and amortization	(2,108)	(898)
Property and equipment—net	35,637	3,154
Laboratory Equipment
Property Plant And Equipment [Line Items]
Property and equipment, at cost	9,309	3,714
Computers and Purchased Software
Property Plant And Equipment [Line Items]
Property and equipment, at cost	248	253
Furniture and Fixtures
Property Plant And Equipment [Line Items]
Property and equipment, at cost	1,066	51
Leasehold Improvements
Property Plant And Equipment [Line Items]
Property and equipment, at cost	24,520	$ 34
Assets Not Yet in Service
Property Plant And Equipment [Line Items]
Property and equipment, at cost	$ 2,602