Leases - Summary of Components of Operating Lease Expense (Detail) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2019
Lessee Lease Description [Line Items]
Total operating lease expense	$ 377	$ 754
Research and Development Expense [Member]
Lessee Lease Description [Line Items]
Fixed operating lease expense	151	296
Variable operating lease expense	14	27
General and Administrative Expense [Member]
Lessee Lease Description [Line Items]
Fixed operating lease expense	165	336
Variable operating lease expense	$ 47	$ 95