Shareholders' Equity - Summary of Dividends Declared and Paid Per Share (Details) - $ / shares	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014	Dec. 31, 2014
Cumulative convertible preferred shares, dividend rate			5.417%		5.417%
Common Shares
Dividends declared per common share			$ 1.74	$ 1.560
Dividends paid per common share			1.74	1.560
5.417% Series 1 Cumulative Convertible Preferred Shares
Dividends declared per preferred share			0.677	0.677
Dividends paid per preferred share			$ 0.677	$ 0.677
Cumulative convertible preferred shares, dividend rate	5.417%	5.417%	5.417%	5.417%