Debt (Narrative) (Details) (USD $)
In Millions, unless otherwise specified |
3 Months Ended | 3 Months Ended | 3 Months Ended | |||||||
---|---|---|---|---|---|---|---|---|---|---|
Mar. 31, 2011
|
Mar. 31, 2012
|
Dec. 31, 2011
|
Mar. 30, 2011
|
Mar. 31, 2012
Unsecured Letter Of Credit Facility [Member]
|
Dec. 31, 2011
Unsecured Letter Of Credit Facility [Member]
|
Mar. 31, 2012
Letter Of Credit [Member]
|
Dec. 31, 2011
Letter Of Credit [Member]
|
Mar. 31, 2012
Unsecured revolving credit facility [Member]
|
Mar. 30, 2011
Unsecured revolving credit facility [Member]
|
|
Debt Instrument | ||||||||||
Maximum borrowing capacity | $ 200.0 | $ 190.0 | $ 250.0 | |||||||
Credit Facility termination date | Mar. 30, 2011 | |||||||||
Credit facility expiration date | June 2014 | June 2012 | ||||||||
Line of Credit Facility, Amount Outstanding | 0 | |||||||||
Cash collateral for borrowed securities | 250.0 | |||||||||
Write-off of unamortized issuance costs | 1.3 | |||||||||
Letters of Credit Outstanding, Amount | $ 219.3 | $ 235.9 | $ 148.0 | $ 152.7 | $ 71.3 | $ 83.2 |