Summary of Operating Results and Certain Other Financial Data (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Segment Reporting Information [Line Items]
Revenue	$ 1,095,971	$ 892,756
Transportation costs	973,180	791,171
Gross margin	122,791	101,585
Costs and expenses:
Salaries and benefits	56,007	43,179
Agent fees and commissions	19,142	17,993
General and administrative	20,504	20,824
Depreciation and amortization	4,005	2,412
Total costs and expenses	99,658	84,408
Operating income	23,133	17,177
Capital Expenditures	22,179	6,625
Operating Segments [Member] | Hub [Member]
Segment Reporting Information [Line Items]
Revenue	831,585	676,480
Transportation costs	741,211	604,674
Gross margin	90,374	71,806
Costs and expenses:
Salaries and benefits	52,070	39,596
Agent fees and commissions	13	17
General and administrative	18,402	18,479
Depreciation and amortization	3,760	2,109
Total costs and expenses	74,245	60,201
Operating income	16,129	11,605
Capital Expenditures	21,537	6,625
Operating Segments [Member] | Mode LLC [Member]
Segment Reporting Information [Line Items]
Revenue	287,899	241,834
Transportation costs	255,482	212,055
Gross margin	32,417	29,779
Costs and expenses:
Salaries and benefits	3,937	3,583
Agent fees and commissions	19,129	17,976
General and administrative	2,102	2,345
Depreciation and amortization	245	303
Total costs and expenses	25,413	24,207
Operating income	7,004	5,572
Capital Expenditures	642
Intersegment Elims [Member]
Segment Reporting Information [Line Items]
Revenue	(23,513)	(25,558)
Transportation costs	$ (23,513)	$ (25,558)