Shareholders' Equity (Summary of Dividends) (Details) - $ / shares	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015	Dec. 31, 2015
Dividends [Line Items]
Series 1 Cumulative Convertible Preferred Shares Interest Rate			5.417%		5.417%
Common shares
Dividends [Line Items]
Dividends declared per common share			$ 2.86	$ 2.680
Dividends paid per common share			$ 2.82	$ 2.610
5.417% Series 1 Cumulative Convertible Preferred shares
Dividends [Line Items]
Series 1 Cumulative Convertible Preferred Shares Interest Rate	5.417%	5.417%	5.417%	5.417%
Dividends declared per preferred share			$ 1.016	$ 1.016
Dividends paid per preferred share			$ 1.016	$ 1.016