Receivables (Details) (USD $)	3 Months Ended	12 Months Ended
	Mar. 31, 2012	Dec. 31, 2011
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross receivables	$ 236,566,000	$ 216,732,000
Allowance for doubtful accounts receivable	(803,000)	(125,000)
Net receivables	235,763,000	216,607,000
Bad debt expense	100,000	100,000
Accounts Receivable [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross receivables	233,585,000	214,608,000
Notes Receivable [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross receivables	0	16,000
Other Receivables [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross receivables	$ 2,981,000	$ 2,108,000