Acquisitions (Details Textual) (USD $)	12 Months Ended		11 Months Ended	12 Months Ended				12 Months Ended						12 Months Ended		4 Months Ended	12 Months Ended				12 Months Ended				12 Months Ended							12 Months Ended					12 Months Ended						12 Months Ended							12 Months Ended						12 Months Ended							12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2011 Morgan Southern	Dec. 31, 2012 Morgan Southern	Dec. 31, 2011 Morgan Southern	Dec. 31, 2010 Morgan Southern	Feb. 04, 2011 Morgan Southern	Dec. 31, 2012 Bruenger	May 31, 2011 Bruenger	Dec. 31, 2012 Bruenger 2012	Dec. 31, 2012 Bruenger 2013	Dec. 31, 2012 Bruenger 2014	May 31, 2011 Bruenger TL	Dec. 31, 2012 James Brooks	Aug. 01, 2011 James Brooks	Dec. 31, 2012 Prime	Dec. 31, 2012 Prime	Dec. 31, 2011 Prime	Dec. 31, 2010 Prime	Aug. 31, 2011 Prime	Dec. 31, 2012 CTL	Feb. 24, 2012 CTL	Dec. 31, 2012 CTL 2013	Feb. 24, 2012 CTL TMS	Dec. 31, 2012 D&E	Apr. 19, 2012 D&E	Dec. 31, 2012 D&E 2013	Dec. 31, 2012 D&E 2014	Apr. 19, 2012 D&E Maximum	Apr. 19, 2012 D&E Minimum	Apr. 19, 2012 D&E TL	Dec. 31, 2012 CTW	Jun. 04, 2012 CTW	Dec. 31, 2012 CTW 2013	Dec. 31, 2012 CTW 2014	Jun. 04, 2012 CTW TL	Dec. 31, 2012 R&M	Aug. 01, 2012 R&M	Dec. 31, 2012 R&M 2013	Dec. 31, 2012 R&M 2014	Dec. 31, 2012 R&M 2015	Aug. 01, 2012 R&M TL	Dec. 31, 2012 EFS	Aug. 10, 2012 EFS	Dec. 31, 2012 EFS 2013	Dec. 31, 2012 EFS 2014	Dec. 31, 2012 EFS 2015	Dec. 31, 2012 EFS 2016	Aug. 10, 2012 EFS LTL	Dec. 31, 2012 DCT	Dec. 21, 2012 DCT	Dec. 31, 2012 DCT 2013	Dec. 31, 2012 DCT 2014	Dec. 31, 2012 DCT 2015	Dec. 21, 2012 DCT TL	Dec. 31, 2012 Central Cal	Nov. 05, 2012 Central Cal	Dec. 31, 2012 Central Cal 2013	Dec. 31, 2012 Central Cal 2014	Dec. 31, 2012 Central Cal 2015	Dec. 31, 2012 Central Cal 2016	Nov. 05, 2012 Central Cal TL	Dec. 31, 2012 A&A	Nov. 12, 2012 A&A	Dec. 31, 2012 A&A 2013	Nov. 12, 2012 A&A TL
Business Acquisition [Line Items]
Date of acquisition				Feb. 04, 2011				May 31, 2011						Aug. 01, 2011			Aug. 31, 2011				Feb. 24, 2012				Apr. 19, 2012							Jun. 04, 2012					Aug. 01, 2012						Aug. 10, 2012							Dec. 21, 2012						Nov. 05, 2012							Nov. 12, 2012
Cash consideration paid to acquire							$ 19,400,000		$ 10,600,000						$ 7,600,000					$ 96,800,000		$ 6,200,000				$ 11,400,000							$ 7,600,000					$ 24,200,000						$ 10,000,000											$ 1,000,000		$ 3,800,000									$ 24,100,000
Proceeds from issuance of common stock																				3,000,000
Contingent consideration, capped earn out									3,000,000													800,000							700,000	100,000			3,500,000					5,000,000						4,000,000							1,000,000						4,000,000							2,500,000
Receive a payment equal to the amount by which entity adjusted operating income, as defined in purchase agreement								1,100,000		2,100,000	2,100,000	2,100,000											1,800,000		5,000,000		2,000,000	2,000,000						2,000,000	2,000,000		1,700,000		4,500,000	4,500,000	4,500,000		900,000		2,300,000	2,500,000	2,500,000	2,800,000				400,000	400,000	400,000		800,000		1,400,000	1,400,000	1,400,000	1,400,000				3,000,000
Contingent purchase price related to acquisitions	20,907,000	3,015,000											2,600,000											700,000							1,000,000					2,600,000						4,200,000							3,100,000						1,000,000							3,100,000				1,900,000
Measurement period adjustment, deferred tax liabilities																	300,000
Measurement period adjustment, goodwill														565,000			300,000
Provisional information, initial accounting incomplete, adjustment														(565,000)			590,000
Revenue of acquiree since acquisition date, actual	73,700,000		63,300,000													29,900,000
Net income of acquiree since acquisition date, actual	5,300,000		2,000,000													1,400,000
Impact on revenue on a pro forma basis	1,185,913,000	1,037,303,000			848,327,000	690,078,000												894,127,000	699,592,000
Impact on net income on a pro forma basis	$ 38,850,000	$ 28,688,000			$ 26,098,000	$ 3,105,000												$ 28,871,000	$ 4,826,000
Impact on Basic EPS on a pro forma basis					$ 0.86	$ 0.12												$ 0.94	$ 0.19
Impact on Diluted EPS on a pro forma basis					$ 0.83	$ 0.12												$ 0.91	$ 0.18