Dividends (Details) - $ / shares		12 Months Ended
	Nov. 04, 2015	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Dividends [Abstract]
Common shares, declared	$ 0.94	$ 3.620	$ 3.300	$ 3.020
5.417% Series 1 Cumulative Convertible Preferred shares, declared		1.354	1.354	1.354
Common shares, paid		3.550	3.210	2.970
5.417% Series 1 Cumulative Convertible Preferred shares, paid		1.354	1.354	1.354
Common shares, ordinary dividend		3.515	3.178	2.911
Common shares, capital gain		0.035	0.032	0.059
5.417% Series 1 Cumulative Convertible Preferred shares, ordinary dividend		1.340	1.340	1.327
5.417% Series 1 Cumulative Convertible Preferred shares, capital gain		$ 0.014	$ 0.014	$ 0.027
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%