Property and Equipment, net - Summary of Property and Equipment, Net (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Property, Plant and Equipment [Line Items]
Total property and equipment, gross	$ 43,376	$ 25,875
Accumulated Depreciation	(12,046)	(7,375)
Total property and equipment, net	31,330	18,500
Computer Equipment [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment, gross	727	443
Furniture, Fixtures, and Other [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment, gross	3,215	2,453
Laboratory Equipment [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment, gross	16,640	8,964
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment, gross	21,400	13,776
Construction Work in Process [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment, gross	$ 1,394	$ 239