Leases - Schedule of Operating Lease Expenses (Detail) $ in Thousands	3 Months Ended
	Mar. 31, 2019 USD ($)
Lessee Lease Description [Line Items]
Total lease costs	$ 1,730
Operating and Maintenance [Member]
Lessee Lease Description [Line Items]
Total lease costs	1,018
General and Administrative [Member]
Lessee Lease Description [Line Items]
Total lease costs	$ 712