Long-Term Debt Obligations (Details) (USD $)	3 Months Ended		6 Months Ended			6 Months Ended								6 Months Ended			6 Months Ended		6 Months Ended											1 Months Ended			1 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012	Dec. 31, 2012	Jun. 30, 2013 Revolving credit facility item	Jun. 25, 2013 Revolving credit facility	Jun. 24, 2013 Revolving credit facility	Jun. 30, 2013 Revolving credit facility EAS	Jun. 30, 2013 Revolving credit facility Through December 31, 2014	Jun. 30, 2013 Revolving credit facility Through December 31, 2015	Jun. 30, 2013 Revolving credit facility Through maturity	Jun. 30, 2013 Revolving credit facility Actual	Jun. 30, 2013 Revolving credit facility Minimum	Jun. 30, 2013 Revolving credit facility Minimum Covenant Requirement	Jun. 30, 2013 Revolving credit facility Minimum Actual	Jun. 30, 2013 Revolving credit facility Maximum	Jun. 30, 2013 Revolving credit facility Maximum Covenant Requirement	Jun. 30, 2013 Revolving credit facility Maximum Actual	Jun. 30, 2013 Revolving credit facility Base rate Consolidated Total Indebtedness to Credit Facility Adjusted EBITDA: Less than 0.75	Jun. 30, 2013 Revolving credit facility Base rate Consolidated Total Indebtedness to Credit Facility Adjusted EBITDA: 0.75 to 1.50	Jun. 30, 2013 Revolving credit facility Base rate Consolidated Total Indebtedness to Credit Facility Adjusted EBITDA: 1.50 to 2.25	Jun. 30, 2013 Revolving credit facility Base rate Consolidated Total Indebtedness to Credit Facility Adjusted EBITDA: 2.25 or greater	Jun. 30, 2013 Revolving credit facility Eurodollar rate Consolidated Total Indebtedness to Credit Facility Adjusted EBITDA: Less than 0.75	Jun. 30, 2013 Revolving credit facility Eurodollar rate Consolidated Total Indebtedness to Credit Facility Adjusted EBITDA: 0.75 to 1.50	Jun. 30, 2013 Revolving credit facility Eurodollar rate Consolidated Total Indebtedness to Credit Facility Adjusted EBITDA: 1.50 to 2.25	Jun. 30, 2013 Revolving credit facility Eurodollar rate Consolidated Total Indebtedness to Credit Facility Adjusted EBITDA: 2.25 or greater	Jun. 30, 2013 Other debt	Dec. 31, 2012 Other debt	Jul. 31, 2013 Other debt Subsequent events	Jun. 30, 2013 Notes to former owners	Dec. 31, 2012 Notes to former owners	Jul. 31, 2013 Notes to former owners Subsequent events
Long-Term Debt Obligations
Total debt	$ 5,400,000		$ 5,400,000		$ 7,400,000																							$ 2,400,000	$ 2,400,000		$ 3,000,000	$ 5,000,000
Less - current portion	(300,000)		(300,000)		(300,000)
Total long-term portion of debt	5,100,000		5,100,000		7,100,000
Borrowing capacity							175,000,000	125,000,000	2,500,000
Financing and professional cost							600,000
Unamortized costs							700,000
Outstanding borrowings						0
Letters of credit amount outstanding						53,200,000
Credit available						121,800,000			2,500,000
Number of interest rate options						2
Additional per annum interest margin added under:
Variable rate basis																				Base rate	Base rate	Base rate	Base rate	Eurodollar rate	Eurodollar rate	Eurodollar rate	Eurodollar rate
Additional per annum interest margin (as a percent)																				0.25%	0.50%	0.75%	1.00%	1.25%	1.50%	1.75%	2.00%
Weighted average interest rate (as a percent)						1.70%			2.70%																			0.30%			3.30%
Payments of debt	2,000,000	4,000,000	2,000,000	4,100,000																										2,400,000			1,000,000
Letter of credit fees (as a percent)														1.25%			2.00%
Commitment fees payable on unused portion of the facility (as a percent)														0.20%			0.35%
Principal financial covenants
Leverage ratio						0.09				3.00	2.75	2.50
Net leverage ratio used to determine exclusion of stock repurchases and the payment of dividends for calculation of the fixed charge coverage ratio																		1.50
Amount of stock repurchases to maintain maximum net leverage ratio																			25,000,000
Net leverage ratio after giving effect to stock repurchases for calculation of the fixed charge coverage ratio																			1.50
Number of quarters of capital expenditures, tax provision, dividends and stock repurchase payments used for calculation of fixed charge coverage ratio						4
Fixed charge coverage ratio													21.37			2.00
Permitted amount of acquisitions per transaction																	20,000,000
Aggregate purchase price of current acquisition and acquisitions in the preceding 12 month period for determining permitted amount of acquisition per transaction																	$ 50,000,000
Net leverage ratio used as basis for other restrictions															2.00