Dividends (Details) (USD $)	0 Months Ended	12 Months Ended
	Nov. 02, 2011	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Dividends [Line Items]
Preferred Shares, percentage		5.417%	5.417%	5.417%
Common Stock, Ordinary Dividends, Tax Rate		15.00%	15.00%	15.00%
Preferred Stock, Ordinary Dividends, Tax Rate		15.00%	15.00%	15.00%
Common Stock [Member]
Dividends [Line Items]
Common shares	$ 0.690	$ 2.720	$ 2.660	$ 2.620
Common shares, ordinary dividend		$ 2.349	$ 2.519	$ 2.377
Common shares, ordinary dividend eligible for 15% rate		$ 0.027	$ 0.025	$ 0.024
Common shares, return of capital		$ 0.162	$ 0.106	$ 0.183
Common shares, capital gain		$ 0.162	$ 0.000	$ 0.026
Common shares, paid		$ 2.700	$ 2.650	$ 2.610
5.417% Series 1 Cumulative Convertible Preferred [Member]
Dividends [Line Items]
5.417% Series 1 Cumulative Convertible Preferred, Declared (in dollars per share)		$ 1.354	$ 1.354	$ 1.354
5.417% Series 1 Cumulative Convertible Preferred shares, ordinary dividend		$ 1.246	$ 1.341	$ 1.246
5.417% Series 1 Cumulative Convertible Preferred shares, ordinary dividend eligible for 15 % rate		$ 0.013	$ 0.013	$ 0.095
5.417% Series 1 Cumulative Convertible Preferred shares, capital gain		$ 0.095	$ 0.000	$ 0.013
5.417% Series 1 Cumulative Convertible Preferred shares, paid		$ 1.354	$ 1.354	$ 1.354