Leases - Schedule of Operating Lease Costs (Detail) $ in Thousands	9 Months Ended
	Sep. 30, 2019 USD ($)
Lessee Lease Description [Line Items]
Total lease costs	$ 780
Operations Yards [Member]
Lessee Lease Description [Line Items]
Total lease costs	439
Office Rent [Member]
Lessee Lease Description [Line Items]
Total lease costs	176
Vehicles [Member]
Lessee Lease Description [Line Items]
Total lease costs	103
Other [Member]
Lessee Lease Description [Line Items]
Total lease costs	$ 62