Notes Payable (Details) (USD $) In Millions, unless otherwise specified | 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] | |||||
| Notes Payable | $ 675.4 | $ 675.4 | $ 609.8 | ||
| Line of Credit Facility, Maximum Borrowing Capacity | 180.0 | 180.0 | 245.0 | ||
| Interest Expense before Capitalization of Interest | 10.0 | 8.6 | 29.8 | 25.7 | |
| Capitalization of Interest | (0.7) | (0.5) | (1.8) | (1.3) | |
| Interest Expense | 9.3 | 8.1 | 28.0 | 24.4 | |
| Interest Paid | 0.4 | 0.3 | 19.4 | 16.5 | |
Notes Payable under Revolving Credit Agreement | |||||
| Debt Instrument [Line Items] | |||||
| Notes Payable | 65.0 | 65.0 | 0 | ||
| Interest Expense before Capitalization of Interest | 0.6 | 0.4 | 1.5 | 1.3 | |
| Interest Paid | 0.3 | 0.2 | 0.5 | 0.5 | |
Senior Subordinated Notes [Member] | Senior Notes, 6 Percent Due May 15, 2017 [Member] | |||||
| Debt Instrument [Line Items] | |||||
| Notes Payable | 356.7 | 356.7 | 356.3 | ||
| Notes Payable, Interest Rate, Stated Percentage | 6.00% | 6.00% | |||
| Interest Expense before Capitalization of Interest | 5.5 | 5.5 | 16.5 | 16.5 | |
| Interest Paid | 0 | 0 | 10.8 | 10.8 | |
Senior Subordinated Notes [Member] | Senior Notes, 6 Percent Due November 30, 2015 [Member] | |||||
| Debt Instrument [Line Items] | |||||
| Notes Payable | 248.1 | 248.1 | 247.8 | ||
| Notes Payable, Interest Rate, Stated Percentage | 6.00% | 6.00% | |||
| Interest Expense before Capitalization of Interest | 3.8 | 0 | 11.5 | 0 | |
| Interest Paid | 0 | 0 | 7.8 | 0 | |
Senior Subordinated Notes [Member] | Senior Notes, 4 Point 875 Due November 1, 2010 [Member] | |||||
| Debt Instrument [Line Items] | |||||
| Notes Payable, Interest Rate, Stated Percentage | 4.875% | 4.875% | |||
| Interest Expense before Capitalization of Interest | 0 | 2.6 | 0 | 7.6 | |
| Interest Paid | 0 | 0 | 0 | 4.9 | |
Mortgage Note Payabe at Amortized Cost [Member] | |||||
| Debt Instrument [Line Items] | |||||
| Notes Payable | 5.6 | 5.6 | 5.7 | ||
| Interest Expense before Capitalization of Interest | 0.1 | 0.1 | 0.3 | 0.3 | |
| Interest Paid | $ 0.1 | $ 0.1 | $ 0.3 | $ 0.3 | |