Summary of Operating Results (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Segment Reporting Information [Line Items]
Revenue	$ 855,557	$ 899,513	$ 1,661,416	$ 1,735,454
Transportation costs	741,067	797,784	1,438,539	1,544,597
Gross margin	114,490	101,729	222,877	190,857
Costs and expenses:
Salaries and benefits	43,602	38,837	87,465	78,313
Agent fees and commissions	18,360	16,686	35,262	31,512
General and administrative	16,083	14,763	32,727	28,834
Depreciation and amortization	2,148	1,967	4,283	3,927
Total costs and expenses	80,193	72,253	159,737	142,586
Operating income	34,297	29,476	63,140	48,271
Capital Expenditures	20,324	8,659	25,217	23,716
Operating Segments [Member] | Hub [Member]
Segment Reporting Information [Line Items]
Revenue	648,523	686,451	1,263,751	1,329,894
Transportation costs	565,448	614,289	1,101,522	1,194,547
Gross margin	83,075	72,162	162,229	135,347
Costs and expenses:
Salaries and benefits	39,787	35,288	79,883	70,948
Agent fees and commissions	13	14	27	29
General and administrative	14,226	13,194	28,948	25,392
Depreciation and amortization	1,830	1,647	3,644	3,265
Total costs and expenses	55,856	50,143	112,502	99,634
Operating income	27,219	22,019	49,727	35,713
Capital Expenditures	20,314	8,550	24,945	23,548
Operating Segments [Member] | Mode LLC [Member]
Segment Reporting Information [Line Items]
Revenue	231,924	233,847	440,755	447,369
Transportation costs	200,509	204,280	380,107	391,859
Gross margin	31,415	29,567	60,648	55,510
Costs and expenses:
Salaries and benefits	3,815	3,549	7,582	7,365
Agent fees and commissions	18,347	16,672	35,235	31,483
General and administrative	1,857	1,569	3,779	3,442
Depreciation and amortization	318	320	639	662
Total costs and expenses	24,337	22,110	47,235	42,952
Operating income	7,078	7,457	13,413	12,558
Capital Expenditures	10	109	272	168
Intersegment Elims [Member]
Segment Reporting Information [Line Items]
Revenue	(24,890)	(20,785)	(43,090)	(41,809)
Transportation costs	$ (24,890)	$ (20,785)	$ (43,090)	$ (41,809)