Description of Business and Summary of Accounting Policies - Additional Information (Detail) $ in Millions	12 Months Ended
	Dec. 31, 2016 USD ($) Segment Customer	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)
Description of Business and Summary of Significant Accounting Policies [Line Items]
Number of operating segments | Segment	1
Depreciation	$ 74.5	$ 63.4	$ 58.4
Primary payroll-related costs capitalized	$ 1.6	2.2	1.0
Stock-based awards compensation expense amortization period	3 years
Advertising costs	$ 1.2	1.7	$ 1.9
Product Concentration Risk [Member] | Sales Revenue, Net [Member]
Description of Business and Summary of Significant Accounting Policies [Line Items]
Number of customers | Customer	0
Percentage of consolidated operating revenue	6.00%
Trailers [Member]
Description of Business and Summary of Significant Accounting Policies [Line Items]
Assets acquired under capital lease, gross	$ 72.8	40.9
Assets acquired under capital lease, accumulated depreciation	$ 6.8	$ 2.2
Minimum [Member]
Description of Business and Summary of Significant Accounting Policies [Line Items]
Percentage of revenue derived from transporting	99.00%