Summary of Preliminary Allocation of Total Purchase Price to Assets and Liabilities (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Jul. 01, 2017	Dec. 31, 2016	Dec. 31, 2015
Business Acquisition [Line Items]
Goodwill	$ 348,661		$ 262,376	$ 262,594
Estenson Logistics, LLC [Member]
Business Acquisition [Line Items]
Cash and cash equivalents		$ 12
Accounts receivable trade		26,830
Accounts receivable other		165
Prepaid expenses and other current assets		1,500
Property and equipment		128,477
Other intangibles		66,400
Goodwill		86,504
Other assets		64
Total assets acquired		309,952
Accounts payable trade		4,542
Accrued payroll		5,661
Accrued other		15,058
Equipment debt assumed		112,677
Total liabilities assumed	$ 5,900	137,938
Total consideration		$ 172,014