Property and Equipment, Net - Summary of Property and Equipment, Net (Detail) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Property, Plant and Equipment [Line Items]
Property plant and equipment, gross	$ 3,662	$ 3,018
Less: Accumulated depreciation and amortization	(989)	(384)
Property plant and equipment, net	2,673	2,634
Laboratory and Office Equipment [Member]
Property, Plant and Equipment [Line Items]
Property plant and equipment, gross	2,188	1,624
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Property plant and equipment, gross	1,260	1,260
Computer Equipment and Software [Member]
Property, Plant and Equipment [Line Items]
Property plant and equipment, gross	134	$ 134
Construction in Process [Member]
Property, Plant and Equipment [Line Items]
Property plant and equipment, gross	$ 80