Preferred Stocks (Details) (USD $) In Thousands, except Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Class of Stock [Line Items]
Preferred stocks	$ 15,000	$ 15,000
Preferred stock redemption price upon liquidation (in dollars per share)	$ 100.00
Cumulative Preferred Stock, Par Value $100 Issuable in Series [Member]
Class of Stock [Line Items]
Authorized Preferred cumulative shares (in shares)	500,000	500,000
Cumulative Preferred shares, par value (in dollars per share)	$ 100.00	$ 100.00
Preferred Stock, Series 4.50% [Member]
Class of Stock [Line Items]
Preferred stocks	10,000	10,000
Preferred Stock, $100 Par Value	4.50%	4.50%	4.50%
Preferred shares outstanding (in shares)	100,000	100,000
Preferred stock redemption price at the option of the company (in dollars per share)	$ 105.00
Preferred Stock, Dividends Per Share, Declared	$ 4.50	$ 4.50	$ 4.50
Preferred Stock, Series 4.70% [Member]
Class of Stock [Line Items]
Preferred stocks	$ 5,000	$ 5,000
Preferred Stock, $100 Par Value	4.70%	4.70%	4.70%
Preferred shares outstanding (in shares)	50,000	50,000
Preferred stock redemption price at the option of the company (in dollars per share)	$ 102.00
Preferred Stock, Dividends Per Share, Declared	$ 4.70	$ 4.70	$ 4.70
Cumulative Preferred Stock A, Without Par Value, Issuable in Series [Member]
Class of Stock [Line Items]
Authorized Preferred cumulative shares (in shares)	1,000,000	1,000,000
Cumulative Preference Stock , Without Par Value, Issuable in Series [Member]
Class of Stock [Line Items]
Authorized Preferred cumulative shares (in shares)	500,000	500,000