Components of Other Intangible Acquired (Detail) - Estenson Logistics, LLC [Member] $ in Thousands	3 Months Ended
	Mar. 31, 2018 USD ($)
Customer Relationships [Member]
Other Intangible Assets [Line Items]
Finite-lived intangible assets, Gross Amount	$ 66,000
Finite-lived intangible assets, Accumulated Amortization	3,300
Finite-lived intangible assets, Net Carrying Value	$ 62,700
Intangible assets estimated useful life	15 years
Trade Name [Member]
Other Intangible Assets [Line Items]
Finite-lived intangible assets, Gross Amount	$ 400
Finite-lived intangible assets, Accumulated Amortization	400
Finite-lived intangible assets, Net Carrying Value	$ 0
Intangible assets estimated useful life	3 months