Commitments and Contingencies (Details Textual) (USD $)	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Commitments and Contingencies (Textual) [Abstract]
Terms of operating lease	one to six years
Total rental expenses for operating leases	$ 24,200,000	$ 25,400,000	$ 29,400,000
Accrued liabilities for unpaid claims incurred	1,200,000	1,200,000
Accrued liabilities for unsecured portion of claims	3,200,000	2,500,000
Accrued asset retirement obligation	2,100,000	1,900,000
Term of estimated claims expected to be paid	1 year
Health Claims [Member]
Loss Contingencies [Line Items]
Claims insured by third party insurers	200,000
General Liability [Member]
Loss Contingencies [Line Items]
Claims insured by third party insurers	750,000
Guarantee Obligations [Member]
Loss Contingencies [Line Items]
Guarantee obligations due to closure of bonds	8,600,000	8,600,000
Letters of Credit in Favor of Insurance Company [Member]
Loss Contingencies [Line Items]
Letters of credit in favor of insurance companies	$ 3,600,000	$ 3,600,000