Senior Notes (Outstanding Senior Notes) (Details) (USD $)	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010
5.40% Senior Notes [Member]
Debt Instrument [Line Items]
Date Issued	10/12/2004
Date Due	Oct. 15, 2014
Principal Amounts	$ 250,000,000
Consolidated Balance Sheet Amount	249,858,000	249,812,000
Market Value	251,370,000	267,500,000
Debt instrument, interest rate, stated percentage	5.40%
8.75% Senior Notes [Member]
Debt Instrument [Line Items]
Date Issued	03/14/2000
Date Due	Mar. 15, 2010
Principal Amounts	$ 200,000,000
Debt instrument, interest rate, stated percentage	8.75%