Acquisitions (Details Textual) (USD $)	3 Months Ended		9 Months Ended		0 Months Ended	9 Months Ended	0 Months Ended	9 Months Ended	0 Months Ended	9 Months Ended	0 Months Ended	9 Months Ended	0 Months Ended	9 Months Ended	0 Months Ended	9 Months Ended			0 Months Ended	9 Months Ended	0 Months Ended	9 Months Ended	0 Months Ended	9 Months Ended	0 Months Ended	9 Months Ended	0 Months Ended	9 Months Ended	0 Months Ended	9 Months Ended	3 Months Ended	9 Months Ended					3 Months Ended		9 Months Ended																																														0 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Feb. 24, 2013 CTL [Member]	Sep. 30, 2013 CTL [Member]	Apr. 19, 2012 D&E [Member]	Sep. 30, 2013 D&E [Member]	Jun. 04, 2012 CTW [Member]	Sep. 30, 2013 CTW [Member]	Aug. 01, 2012 R & M [Member]	Sep. 30, 2013 R & M [Member]	Aug. 10, 2012 EFS [Member]	Sep. 30, 2013 EFS [Member]	Nov. 05, 2012 Central Cal [Member]	Sep. 30, 2013 Central Cal [Member]	Sep. 30, 2013 A&A [Member]	Sep. 30, 2013 DCT [Member]	Apr. 30, 2013 Wando [Member]	Sep. 30, 2013 Wando [Member]	Apr. 30, 2013 Adrian [Member]	Sep. 30, 2013 Adrian [Member]	Jul. 25, 2013 Marisol [Member]	Sep. 30, 2013 Marisol [Member]	Aug. 15, 2013 TA Drayage [Member]	Sep. 30, 2013 TA Drayage [Member]	Sep. 11, 2013 GW Palmer [Member]	Sep. 30, 2013 GW Palmer [Member]	Sep. 18, 2013 YES Trans [Member]	Sep. 30, 2013 YES Trans [Member]	Sep. 30, 2012 2012 [Member]	Sep. 30, 2012 2012 [Member]	Sep. 30, 2013 2012 [Member] CTL [Member]	Sep. 30, 2013 2012 [Member] D&E [Member]	Sep. 30, 2013 2012 [Member] CTW [Member]	Sep. 30, 2013 2012 [Member] EFS [Member]	Sep. 30, 2013 2013 [Member]	Sep. 30, 2012 2013 [Member]	Sep. 30, 2013 2013 [Member]	Sep. 30, 2012 2013 [Member]	Sep. 30, 2013 2013 [Member] CTL [Member]	Sep. 30, 2013 2013 [Member] D&E [Member]	Sep. 30, 2013 2013 [Member] CTW [Member]	Sep. 30, 2013 2013 [Member] R & M [Member]	Sep. 30, 2013 2013 [Member] EFS [Member]	Sep. 30, 2013 2013 [Member] Central Cal [Member]	Sep. 30, 2013 2013 [Member] A&A [Member]	Sep. 30, 2013 2013 [Member] DCT [Member]	Sep. 30, 2013 2013 [Member] GW Palmer [Member]	Sep. 30, 2013 2014 [Member] CTW [Member]	Sep. 30, 2013 2014 [Member] R & M [Member]	Sep. 30, 2013 2014 [Member] EFS [Member]	Sep. 30, 2013 2014 [Member] Central Cal [Member]	Sep. 30, 2013 2014 [Member] A&A [Member]	Sep. 30, 2013 2014 [Member] DCT [Member]	Sep. 30, 2013 2014 [Member] Adrian [Member]	Sep. 30, 2013 2014 [Member] Marisol [Member]	Sep. 30, 2013 2014 [Member] GW Palmer [Member]	Sep. 30, 2013 2014 [Member] YES Trans [Member]	Sep. 30, 2013 2015 [Member] R & M [Member]	Sep. 30, 2013 2015 [Member] EFS [Member]	Sep. 30, 2013 2015 [Member] Central Cal [Member]	Sep. 30, 2013 2015 [Member] A&A [Member]	Sep. 30, 2013 2015 [Member] DCT [Member]	Sep. 30, 2013 2015 [Member] Adrian [Member]	Sep. 30, 2013 2015 [Member] Marisol [Member]	Sep. 30, 2013 2015 [Member] GW Palmer [Member]	Sep. 30, 2013 2015 [Member] YES Trans [Member]	Sep. 30, 2013 2016 [Member] EFS [Member]	Sep. 30, 2013 2016 [Member] Central Cal [Member]	Sep. 30, 2013 2016 [Member] A&A [Member]	Sep. 30, 2013 2016 [Member] Adrian [Member]	Sep. 30, 2013 2016 [Member] GW Palmer [Member]	Sep. 30, 2013 2016 [Member] YES Trans [Member]	Sep. 30, 2013 2017 [Member] Adrian [Member]	Sep. 30, 2013 2017 [Member] GW Palmer [Member]	Sep. 30, 2013 2017 [Member] YES Trans [Member]	Feb. 24, 2012 TMS [Member] CTL [Member]	Apr. 30, 2013 TMS [Member] Adrian [Member]	Jul. 25, 2013 TMS [Member] Marisol [Member]	Apr. 19, 2012 TL [Member] D&E [Member]	Jun. 04, 2012 TL [Member] CTW [Member]	Aug. 01, 2012 TL [Member] R & M [Member]	Nov. 05, 2012 TL [Member] Central Cal [Member]	Nov. 12, 2012 TL [Member] A&A [Member]	Dec. 21, 2012 TL [Member] DCT [Member]	Aug. 10, 2012 LTL [Member] EFS [Member]	Sep. 30, 2013 Maximum [Member] D&E [Member]	Sep. 30, 2013 Minimum [Member] D&E [Member]
Business Acquisition (Textual) [Abstract]
Date of acquisition						Feb. 24, 2012		Apr. 19, 2012		Jun. 04, 2012		Aug. 01, 2012		Aug. 10, 2012		Nov. 05, 2012	Nov. 12, 2012	Dec. 21, 2012		Apr. 30, 2013		Apr. 30, 2013		Jul. 25, 2013		Aug. 15, 2013		Sep. 11, 2013		Sep. 18, 2013
Consideration Transferred					$ 6,200,000		$ 11,400,000		$ 7,600,000		$ 24,200,000		$ 10,000,000		$ 3,800,000				$ 9,000,000		$ 14,200,000		$ 66,000,000		$ 1,200,000		$ 2,500,000		$ 1,200,000																																																								$ 24,100,000	$ 1,000,000
Business Combination, Contingent Consideration Arrangements, Range of Outcomes, Value, High	2,500,000		2,500,000			800,000				3,500,000		5,000,000		4,000,000		4,000,000	2,500,000	1,000,000				6,500,000						2,800,000		1,100,000																800,000			700,000																																							700,000
Business Combination, Contingent Consideration Arrangements, Basis								5,000,000				1,700,000																					1,800,000	2,000,000	2,000,000	900,000					1,800,000	2,000,000	2,000,000	4,500,000	2,300,000	1,400,000	3,000,000	400,000	900,000	2,000,000	4,500,000	2,500,000	1,800,000	3,000,000	400,000	2,300,000	7,800,000	1,000,000	200,000	4,500,000	2,500,000	1,800,000	3,000,000	400,000	2,300,000	7,800,000	1,000,000	200,000	2,800,000	1,800,000	3,000,000	2,300,000	1,000,000	200,000	2,300,000	1,000,000	200,000
Business Combination, Contingent Consideration Arrangements, Range of Outcomes, Value, Low																																																																																									100,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Contingent Liability																																																																														700,000	5,300,000	1,900,000	1,000,000	2,600,000	4,200,000	3,400,000	2,200,000	1,000,000	3,100,000
Revenue of acquiree since acquisition date, actual	32,800,000	23,100,000	40,600,000	32,200,000
Earnings or loss of acquiree since acquisition date, actual	2,100,000	2,500,000	3,200,000	4,300,000
Impact on revenue on a pro forma basis																															297,048,000	884,413,000					377,327,000	328,754,000	1,099,439,000	921,033,000
Impact on net income on a pro forma basis																															$ 9,971,000	$ 29,290,000					$ 13,199,000	$ 10,234,000	$ 37,923,000	$ 28,868,000