Segment Reporting - Summary of Segment Reporting Information (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Segment Reporting Information [Line Items]
Operating revenue	$ 1,006,439	$ 928,103
Operating earnings	43,550	52,033
Depreciation and amortization expense	67,870	63,895
Operating Segments [Member] | Truckload [Member]
Segment Reporting Information [Line Items]
Operating revenue	522,110	490,725
Operating earnings	38,520	42,188
Depreciation and amortization expense	50,413	43,783
Operating Segments [Member] | Intermodal [Member]
Segment Reporting Information [Line Items]
Operating revenue	181,090	184,825
Operating earnings	6,634	7,089
Depreciation and amortization expense	8,026	9,239
Operating Segments [Member] | Logistics [Member]
Segment Reporting Information [Line Items]
Operating revenue	183,904	166,750
Operating earnings	5,183	5,177
Depreciation and amortization expense	99	98
Operating Segments [Member] | Other [Member]
Segment Reporting Information [Line Items]
Operating revenue	50,283	49,549
Operating earnings	(6,787)	(2,421)
Depreciation and amortization expense	9,332	10,775
Operating Segments [Member] | Fuel Surcharge [Member]
Segment Reporting Information [Line Items]
Operating revenue	90,250	56,154
Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Operating revenue	$ (21,198)	$ (19,900)