Debt - Line of Credit (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Jul. 31, 2011	Dec. 31, 2010
Line of Credit Facility [Line Items]
Long-term Line of Credit, Noncurrent	$ 200,000
Line of Credit Facility, Amount Outstanding	74,000
Revolving Credit Facility due in 2016 [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	1,200,000	800,000
Line of Credit Facility, Interest Rate Spread at Period End	1.275%
Line of Credit Facility Commitment Fee Percentage	0.225%
Line of Credit Facility, Amount Outstanding	$ 74,000		$ 0