Leases - Schedule of Operating Lease Expenses (Detail) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2019
Lessee Lease Description [Line Items]
Total lease costs	$ 1,640	$ 4,887
Operating and Maintenance [Member]
Lessee Lease Description [Line Items]
Total lease costs	788	2,822
General and Administrative [Member]
Lessee Lease Description [Line Items]
Total lease costs	$ 852	$ 2,065