Subsequent Event Subsequent Event (Details) (Subsequent Event, USD $)	0 Months Ended
	Mar. 12, 2013	Feb. 28, 2013
Subsequent Event [Line Items]
Unsecured revolving credit facility, current borrowing capacity	$ 200,000,000.0
Unsecured revolving credit facility, expiration date	Mar. 12, 2016
Unsecured revolving credit facility, contingent expiration, senior notes threshold	200,000,000
Unsecured revolving credit facility, maximum borrowing capacity	300,000,000
Unsecured revolving credit facility, significant subsidiary threshold	5.00%
Line of Credit Facility, Non Guarantor Subsidiary Threshold, Percent	10.00%
Number of additional guarantor subsidiaries		12
Letter of Credit
Subsequent Event [Line Items]
Unsecured revolving credit facility, maximum borrowing capacity	$ 100,000,000