Long-Term Debt Obligations (Details) (USD $)			3 Months Ended							3 Months Ended		3 Months Ended				3 Months Ended
	Mar. 31, 2013	Dec. 31, 2012	Mar. 31, 2013 Revolving credit facility item	Sep. 23, 2011 Revolving credit facility	Mar. 31, 2013 Revolving credit facility EAS	Mar. 31, 2013 Revolving credit facility Through December 31, 2013	Mar. 31, 2013 Revolving credit facility Through June 30, 2014	Mar. 31, 2013 Revolving credit facility Through maturity	Mar. 31, 2013 Revolving credit facility Actual	Mar. 31, 2013 Revolving credit facility Minimum	Mar. 31, 2013 Revolving credit facility Minimum Covenant Requirement	Mar. 31, 2013 Revolving credit facility Maximum	Mar. 31, 2013 Revolving credit facility Maximum Covenant Requirement Through December 31, 2013	Mar. 31, 2013 Revolving credit facility Maximum Covenant Requirement Through June 30, 2014	Mar. 31, 2013 Revolving credit facility Maximum Covenant Requirement Through maturity	Mar. 31, 2013 Revolving credit facility Base rate Consolidated Total Indebtedness to Credit Facility Adjusted EBITDA: Less than 0.75	Mar. 31, 2013 Revolving credit facility Base rate Consolidated Total Indebtedness to Credit Facility Adjusted EBITDA: 0.75 to 1.25	Mar. 31, 2013 Revolving credit facility Base rate Consolidated Total Indebtedness to Credit Facility Adjusted EBITDA: 1.25 to 2.00	Mar. 31, 2013 Revolving credit facility Base rate Consolidated Total Indebtedness to Credit Facility Adjusted EBITDA: 2.00 to 2.50	Mar. 31, 2013 Revolving credit facility Base rate Consolidated Total Indebtedness to Credit Facility Adjusted EBITDA: 2.50 or greater	Mar. 31, 2013 Revolving credit facility Eurodollar rate Consolidated Total Indebtedness to Credit Facility Adjusted EBITDA: Less than 0.75	Mar. 31, 2013 Revolving credit facility Eurodollar rate Consolidated Total Indebtedness to Credit Facility Adjusted EBITDA: 0.75 to 1.25	Mar. 31, 2013 Revolving credit facility Eurodollar rate Consolidated Total Indebtedness to Credit Facility Adjusted EBITDA: 1.25 to 2.00	Mar. 31, 2013 Revolving credit facility Eurodollar rate Consolidated Total Indebtedness to Credit Facility Adjusted EBITDA: 2.00 to 2.50	Mar. 31, 2013 Revolving credit facility Eurodollar rate Consolidated Total Indebtedness to Credit Facility Adjusted EBITDA: 2.50 or greater	Mar. 31, 2013 Other debt	Dec. 31, 2012 Other debt	Mar. 31, 2013 Notes to former owners	Dec. 31, 2012 Notes to former owners
Long-Term Debt Obligations
Total debt	$ 7,400,000	$ 7,400,000																								$ 2,400,000	$ 2,400,000	$ 5,000,000	$ 5,000,000
Less - current portion	(300,000)	(300,000)																								(300,000)
Total long-term portion of debt	7,100,000	7,100,000
Borrowing capacity				125,000,000	2,500,000
Outstanding borrowings			0
Letters of credit amount outstanding			53,200,000
Credit available			71,800,000
Number of interest rate options			2
Additional per annum interest margin added under:
Variable rate basis																Base rate	Base rate	Base rate	Base rate	Base rate	Eurodollar rate	Eurodollar rate	Eurodollar rate	Eurodollar rate	Eurodollar rate
Additional per annum interest margin (as a percent)																0.75%	1.00%	1.25%	1.50%	1.75%	1.75%	2.00%	2.25%	2.50%	2.75%
Weighted average interest rate (as a percent)			2.20%																							0.30%		3.30%
Letter of credit fees (as a percent)										1.30%		2.10%
Commitment fees payable on unused portion of the facility (as a percent)										0.25%		0.50%
Principal financial covenants
Leverage ratio			0.14			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													2.00	1.50	1.00
Fixed charge coverage ratio									18.25
Number of quarters of capital expenditures, tax provision, dividends and stock repurchase payments used for calculation of fixed charge coverage ratio			4
Permitted amount of acquisitions per transaction			15,000,000
Period prior to acquisition for which aggregate purchase price is considered for determining permitted amount of acquisitions per transaction			12 months
Aggregate purchase price of current acquisition and acquisitions in the preceding 12 month period for determining permitted amount of acquisition per transaction												$ 30,000,000
Net leverage ratio used as basis for other restrictions											2.00