Receivables (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross receivables	$ 231,446	$ 216,732
Allowance for doubtful accounts receivable	(722)	(125)
Net receivables	230,724	216,607
Accounts receivable [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross receivables	228,708	214,608
Notes receivable [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross receivables	66	16
Other receivables [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross receivables	$ 2,672	$ 2,108