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% | |