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Notes Payable (Details) (USD $)
In Millions, unless otherwise specified |
3 Months Ended | 9 Months Ended | 3 Months Ended | 9 Months Ended | 3 Months Ended | 3 Months Ended | 9 Months Ended | 3 Months Ended | 9 Months Ended | 3 Months Ended | 9 Months Ended | ||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
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Sep. 30, 2012
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Sep. 30, 2011
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Sep. 30, 2012
|
Sep. 30, 2011
|
Dec. 31, 2011
|
Sep. 30, 2012
Notes Payable under Revolving Credit Agreement [Member]
|
Sep. 30, 2011
Notes Payable under Revolving Credit Agreement [Member]
|
Sep. 30, 2012
Notes Payable under Revolving Credit Agreement [Member]
|
Sep. 30, 2011
Notes Payable under Revolving Credit Agreement [Member]
|
Sep. 30, 2012
Notes Payable under Revolving Credit Agreement [Member]
2016 Credit Agreement [Member]
|
Mar. 07, 2012
Notes Payable under Revolving Credit Agreement [Member]
2016 Credit Agreement [Member]
|
Mar. 31, 2012
Notes Payable under Revolving Credit Agreement [Member]
Former Credit Agreement [Member]
|
Mar. 07, 2012
Notes Payable under Revolving Credit Agreement [Member]
Former Credit Agreement [Member]
|
Dec. 31, 2011
Notes Payable under Revolving Credit Agreement [Member]
Former Credit Agreement [Member]
|
Sep. 30, 2012
Senior Subordinated Notes [Member]
Senior Notes, 6 Percent Due May 15, 2017 [Member]
|
Sep. 30, 2011
Senior Subordinated Notes [Member]
Senior Notes, 6 Percent Due May 15, 2017 [Member]
|
Sep. 30, 2012
Senior Subordinated Notes [Member]
Senior Notes, 6 Percent Due May 15, 2017 [Member]
|
Sep. 30, 2011
Senior Subordinated Notes [Member]
Senior Notes, 6 Percent Due May 15, 2017 [Member]
|
Dec. 31, 2011
Senior Subordinated Notes [Member]
Senior Notes, 6 Percent Due May 15, 2017 [Member]
|
Sep. 30, 2012
Senior Subordinated Notes [Member]
Senior Notes, 6 Percent Due November 30, 2015 [Member]
|
Sep. 30, 2011
Senior Subordinated Notes [Member]
Senior Notes, 6 Percent Due November 30, 2015 [Member]
|
Sep. 30, 2012
Senior Subordinated Notes [Member]
Senior Notes, 6 Percent Due November 30, 2015 [Member]
|
Sep. 30, 2011
Senior Subordinated Notes [Member]
Senior Notes, 6 Percent Due November 30, 2015 [Member]
|
Dec. 31, 2011
Senior Subordinated Notes [Member]
Senior Notes, 6 Percent Due November 30, 2015 [Member]
|
Sep. 30, 2012
Mortgage Note Payabe at Amortized Cost [Member]
|
Sep. 30, 2011
Mortgage Note Payabe at Amortized Cost [Member]
|
Sep. 30, 2012
Mortgage Note Payabe at Amortized Cost [Member]
|
Sep. 30, 2011
Mortgage Note Payabe at Amortized Cost [Member]
|
Dec. 31, 2011
Mortgage Note Payabe at Amortized Cost [Member]
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| Debt Instrument [Line Items] | |||||||||||||||||||||||||||||
| Notes Payable | $ 611.2 | $ 611.2 | $ 610.6 | $ 357.2 | $ 357.2 | $ 356.8 | $ 248.5 | $ 248.5 | $ 248.2 | $ 5.5 | $ 5.5 | $ 5.6 | |||||||||||||||||
| Notes Payable, Interest Rate, Stated Percentage | 6.00% | 6.00% | 6.00% | 6.00% | |||||||||||||||||||||||||
| Line of Credit Facility, Maximum Borrowing Capacity | 325.0 | 245.0 | |||||||||||||||||||||||||||
| Line of Credit Facility, Length of Agreement | 4 years | ||||||||||||||||||||||||||||
| Line of Credit Facility, Amount Outstanding | 0 | 0 | 0 | ||||||||||||||||||||||||||
| Line of Credit Facility, Remaining Borrowing Capacity | 325.0 | ||||||||||||||||||||||||||||
| Write off of Deferred Debt Issuance Cost | 0.5 | ||||||||||||||||||||||||||||
| Interest Expense before Capitalization of Interest | 9.8 | 10.0 | 30.1 | 29.8 | 0.3 | 0.6 | 1.6 | 1.5 | 5.5 | 5.5 | 16.6 | 16.5 | 3.9 | 3.8 | 11.6 | 11.5 | 0.1 | 0.1 | 0.3 | 0.3 | |||||||||
| Capitalization of Interest | (0.2) | (0.7) | (1.6) | (1.8) | |||||||||||||||||||||||||
| Interest Expense | 9.6 | 9.3 | 28.5 | 28.0 | |||||||||||||||||||||||||
| Interest Paid | $ 0.3 | $ 0.4 | $ 20.5 | $ 19.4 | $ 0.2 | $ 0.3 | $ 1.9 | $ 0.5 | $ 0 | $ 0 | $ 10.8 | $ 10.8 | $ 0 | $ 0 | $ 7.5 | $ 7.8 | $ 0.1 | $ 0.1 | $ 0.3 | $ 0.3 | |||||||||