Leases - Summary of Components of Operating Lease Expense (Detail) $ in Thousands	3 Months Ended
	Mar. 31, 2019 USD ($)
Lessee Lease Description [Line Items]
Total operating lease expense	$ 377
Research and Development Expense [Member]
Lessee Lease Description [Line Items]
Fixed operating lease expense	145
Variable operating lease expense	13
General and Administrative Expense [Member]
Lessee Lease Description [Line Items]
Fixed operating lease expense	171
Variable operating lease expense	$ 48