Accounts Receivable Securitization (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Dec. 31, 2012
Accounts Receivable - Securitized	$ 30,119		$ 37,846
Increase (Decrease) in Accounts Receivable from Securitization	7,727
AR securitization facility [Member]
Line of Credit Facility, Maximum Borrowing Capacity	200,000
Current borrowing capacity of receivable facility	199,800		200,000
Letters of credit amount outstanding	159,281
Costs associated with the receivables facility	472	419
Expiration date of receivables facility	Mar. 30, 2017
Eligible accounts receivable, a subordinated retained interest	$ 10,400