Shareholders' Equity - Summary of Dividends Declared and Paid Per Share (Details) - $ / shares	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014
Cumulative convertible preferred shares, dividend rate			5.417%		5.417%
Common Shares
Dividends declared per common share			$ 2.68	$ 2.430
Dividends paid per common share			2.61	2.34
5.417% Series 1 Cumulative Convertible Preferred Shares
Dividends declared per preferred share			1.016	1.016
Dividends paid per preferred share			$ 1.016	$ 1.016
Cumulative convertible preferred shares, dividend rate	5.417%	5.417%	5.417%	5.417%