Summary of Operating Results (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Segment Reporting Information [Line Items]
Revenue	$ 978,560	$ 932,814	$ 855,557	$ 805,859	$ 890,272	$ 899,869	$ 899,513	$ 835,941	$ 3,572,790	$ 3,525,595	$ 3,571,126
Transportation costs									3,118,005	3,112,900	3,200,691
Gross margin	120,454	111,454	114,490	108,387	116,774	105,064	101,729	89,128	454,785	412,695	370,435
Costs and expenses:
Salaries and benefits									180,459	158,938	136,480
Agent fees and commissions									72,896	68,724	62,041
General and administrative									68,630	60,015	58,014
Depreciation and amortization									8,966	7,988	7,799
Driver settlements and related costs											10,343
Impairment of software											11,881
Total costs and expenses									330,951	295,665	286,558
Operating income	$ 30,839	$ 29,855	$ 34,297	$ 28,843	$ 35,341	$ 33,418	$ 29,476	$ 18,795	123,834	117,030	83,877
Capital expenditures									107,409	83,042	119,171
Operating Segments [Member] | Hub [Member]
Segment Reporting Information [Line Items]
Revenue									2,734,541	2,679,318	2,722,799
Transportation costs									2,404,946	2,385,197	2,461,144
Gross margin									329,595	294,121	261,655
Costs and expenses:
Salaries and benefits									165,136	143,993	122,097
Agent fees and commissions									66	56	45
General and administrative									60,811	53,023	51,108
Depreciation and amortization									7,698	6,688	6,238
Driver settlements and related costs											10,343
Impairment of software											11,881
Total costs and expenses									233,711	203,760	201,712
Operating income									95,884	90,361	59,943
Capital expenditures									106,316	79,860	118,640
Operating Segments [Member] | Mode LLC [Member]
Segment Reporting Information [Line Items]
Revenue									948,735	928,661	931,131
Transportation costs									823,545	810,087	822,351
Gross margin									125,190	118,574	108,780
Costs and expenses:
Salaries and benefits									15,323	14,945	14,383
Agent fees and commissions									72,830	68,668	61,996
General and administrative									7,819	6,992	6,906
Depreciation and amortization									1,268	1,300	1,561
Total costs and expenses									97,240	91,905	84,846
Operating income									27,950	26,669	23,934
Capital expenditures									1,093	3,182	531
Intersegment Elims [Member]
Segment Reporting Information [Line Items]
Revenue									(110,486)	(82,384)	(82,804)
Transportation costs									$ (110,486)	$ (82,384)	$ (82,804)