Debt Debt, Textuals (Details) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010	Dec. 31, 2010
Debt Instrument [Line Items]
Debt, Weighted Average Interest Rate	6.67%		6.67%		6.80%
Long-term Debt, Percentage Bearing Fixed Interest, Percentage Rate	90.00%		90.00%		93.00%
Line of Credit Facility, Maximum Borrowing Capacity	$ 500,000,000		$ 500,000,000		$ 400,000,000
Letters of Credit, Maximum Borrowing Capacity	175,000,000		175,000,000
Line of Credit Facility, Amount Outstanding	65,000,000		65,000,000		0
Letters of Credit Outstanding, Amount	33,300,000		33,300,000
Line of Credit Facility, Unused Capacity, Commitment Fee Percentage			0.35%
Line of Credit Facility, Remaining Borrowing Capacity	401,700,000		401,700,000
Early extinguishment of debt			43,089,000	118,562,000
Repayments of Debt				30,000,000
Gains (Losses) on Extinguishment of Debt	(1,355,000)	(9,066,000)	(3,504,000)	(9,357,000)
Capital Lease Obligations Incurred			27,100,000	17,300,000
February 2013 [Member]
Debt Instrument [Line Items]
Repayments of Debt			3,900,000	23,100,000
Debt Instrument, Interest Rate, Stated Percentage	7.88%	7.88%	7.88%	7.88%
October 2014 [Member]
Debt Instrument [Line Items]
Repayments of Debt				64,300,000
Debt Instrument, Interest Rate, Stated Percentage		7.38%		7.38%
April 2015 [Member]
Debt Instrument [Line Items]
Repayments of Debt			22,300,000	3,000,000
Debt Instrument, Interest Rate, Stated Percentage	6.75%	6.75%	6.75%	6.75%
April 2016 [Member]
Debt Instrument [Line Items]
Repayments of Debt			$ 16,900,000	$ 20,200,000
Debt Instrument, Interest Rate, Stated Percentage	6.75%	6.75%	6.75%	6.75%