Acquisitions (Details Textual) (USD $)	3 Months Ended	6 Months Ended			6 Months Ended		6 Months Ended		6 Months Ended		6 Months Ended		6 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2012	Jun. 30, 2013 CTL [Member]	Feb. 24, 2012 CTL [Member]	Jun. 30, 2013 D&E [Member]	Apr. 19, 2012 D&E [Member]	Jun. 30, 2013 CTW [Member]	Jun. 04, 2012 CTW [Member]	Jun. 30, 2013 R & M [Member]	Aug. 01, 2012 R & M [Member]	Jun. 30, 2013 EFS [Member]	Aug. 10, 2012 EFS [Member]	Jun. 30, 2013 Central Cal [Member]	Nov. 05, 2012 Central Cal [Member]	Jun. 30, 2013 A&A [Member]	Jun. 30, 2013 DCT [Member]	Jun. 30, 2013 Wando [Member]	Jun. 30, 2013 Adrian [Member]	Jun. 30, 2013 2012 [Member] CTL [Member]	Jun. 30, 2013 2012 [Member] D&E [Member]	Jun. 30, 2013 2012 [Member] CTW [Member]	Jun. 30, 2013 2013 [Member] CTL [Member]	Jun. 30, 2013 2013 [Member] D&E [Member]	Jun. 30, 2013 2013 [Member] CTW [Member]	Jun. 30, 2013 2013 [Member] R & M [Member]	Jun. 30, 2013 2013 [Member] EFS [Member]	Jun. 30, 2013 2013 [Member] Central Cal [Member]	Jun. 30, 2013 2013 [Member] A&A [Member]	Jun. 30, 2013 2013 [Member] DCT [Member]	Jun. 30, 2013 2014 [Member] CTW [Member]	Jun. 30, 2013 2014 [Member] R & M [Member]	Jun. 30, 2013 2014 [Member] EFS [Member]	Jun. 30, 2013 2014 [Member] Central Cal [Member]	Jun. 30, 2013 2014 [Member] A&A [Member]	Jun. 30, 2013 2014 [Member] DCT [Member]	Jun. 30, 2013 2014 [Member] Adrian [Member]	Jun. 30, 2013 2015 [Member] R & M [Member]	Jun. 30, 2013 2015 [Member] EFS [Member]	Jun. 30, 2013 2015 [Member] Central Cal [Member]	Jun. 30, 2013 2015 [Member] A&A [Member]	Jun. 30, 2013 2015 [Member] DCT [Member]	Jun. 30, 2013 2015 [Member] Adrian [Member]	Jun. 30, 2013 2016 [Member] EFS [Member]	Jun. 30, 2013 2016 [Member] Central Cal [Member]	Jun. 30, 2013 2016 [Member] A&A [Member]	Jun. 30, 2013 2016 [Member] Adrian [Member]	Jun. 30, 2013 2017 [Member] Adrian [Member]	Feb. 24, 2012 TMS [Member] CTL [Member]	Apr. 30, 2013 TMS [Member] Adrian [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]	Apr. 30, 2013 TL [Member] Wando [Member]	Aug. 10, 2012 LTL [Member] EFS [Member]	Jun. 30, 2013 Maximum [Member] D&E [Member]	Jun. 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
Total consideration paid to acquire				$ 6,200,000		$ 11,400,000		$ 7,600,000		$ 24,200,000		$ 10,000,000		$ 3,800,000																																			$ 14,200,000					$ 24,100,000	$ 1,000,000	$ 9,000,000
Contingent consideration, capped earn out			800,000				3,500,000		5,000,000		4,000,000		4,000,000		2,500,000	1,000,000		6,500,000																																								700,000	100,000
Receive a payment equal to the amount by which entity annual operating income, as defined in the purchase agreement					5,000,000				1,700,000		900,000		800,000						1,800,000	2,000,000	2,000,000	1,800,000	2,000,000	2,000,000	4,500,000	2,300,000	1,400,000	3,000,000	400,000	2,000,000	4,500,000	2,500,000	1,800,000	3,000,000	400,000	2,300,000	4,500,000	2,500,000	1,800,000	3,000,000	400,000	2,300,000	2,800,000	1,800,000	3,000,000	2,300,000	2,300,000
Contingent purchase price related to acquisitions																																																700,000	5,300,000	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	5,600,000	6,300,000
Impact on revenue on a pro forma basis	300,678,000	587,365,000
Impact on net income on a pro forma basis	10,722,000	19,318,000
Business Combination, Pro Forma Information, Earnings or Loss of Acquiree since Acquisition Date, Actual	$ 1,500,000	$ 1,800,000