Property and Equipment, Net - Schedule of Property and Equipment (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Property Plant And Equipment [Line Items]
Property and equipment, at cost	$ 78,471	$ 31,577
Less: accumulated depreciation	(18,116)	(12,452)
Property and equipment, net	60,355	19,125
Laboratory Equipment
Property Plant And Equipment [Line Items]
Property and equipment, at cost	20,773	14,009
Computer Equipment
Property Plant And Equipment [Line Items]
Property and equipment, at cost	2,450	1,819
Furniture and Office Equipment
Property Plant And Equipment [Line Items]
Property and equipment, at cost	1,568	1,300
Computer Software
Property Plant And Equipment [Line Items]
Property and equipment, at cost	505	429
Construction in Progress
Property Plant And Equipment [Line Items]
Property and equipment, at cost	1,852	3,942
Leasehold Improvements
Property Plant And Equipment [Line Items]
Property and equipment, at cost	14,716	$ 10,078
Build-to-suit Asset Cost
Property Plant And Equipment [Line Items]
Property and equipment, at cost	$ 36,607