Accounts Receivable Securitization (Details) (USD $) In Thousands, unless otherwise specified	9 Months Ended	12 Months Ended
	Sep. 30, 2010	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Letters of credit, maximum borrowing capacity		$ 200,000
Current borrowing capacity of receivable facility		200,000
Costs associated with the receivables facility	(2,676)	(1,986)		(2,990)
Expiration date of receivables facility		April 30, 2012
Eligible accounts receivable		192,700	200,000
Eligible accounts receivable, a subordinated retained interest		192,700
Accounts Receivable—Securitized		0	200,000
Decrease in the accounts receivable securitization program		$ 200,000	$ (150,000)	$ (115,000)