Dividends (Details) (USD $)	0 Months Ended	12 Months Ended
	Oct. 30, 2014	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Dividends [Abstract]
Common shares, declared	$ 0.87	$ 3.300	$ 3.020	$ 2.840
5.417% Series 1 Cumulative Convertible Preferred shares, declared		$ 1.354	$ 1.354	$ 1.354
Common shares, paid		$ 3.210	$ 2.970	$ 2.800
5.417% Series 1 Cumulative Convertible Preferred shares, paid		$ 1.354	$ 1.354	$ 1.354
Common shares, ordinary dividend		$ 3.178	$ 2.911	$ 2.772
Common shares, capital gain		$ 0.032	$ 0.059	$ 0.028
5.417% Series 1 Cumulative Convertible Preferred shares, ordinary dividend		$ 1.340	$ 1.327	$ 1.340
5.417% Series 1 Cumulative Convertible Preferred shares, capital gain		$ 0.014	$ 0.027	$ 0.014
Series 1 Cumulative Convertible Preferred interest rate		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%