Leased Property Under Capital Leases - Additional Information (Detail) $ in Millions	12 Months Ended
	Dec. 31, 2017 USD ($)
Capital Leased Assets [Line Items]
Leased property under capital leases from related party transactions	$ 15.1
Minimum [Member] | Assets Held under Capital Leases [Member]
Capital Leased Assets [Line Items]
Estimated useful lives of leased property under capital lease	3 years
Maximum [Member] | Assets Held under Capital Leases [Member]
Capital Leased Assets [Line Items]
Estimated useful lives of leased property under capital lease	20 years