Subsequent Events (Details) (USD $)	12 Months Ended			0 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Oct. 24, 2014	Feb. 16, 2015
Subsequent Event [Line Items]
Dividends declared per common share (in dollars per share)	$ 0.46	$ 0.38	$ 0.33
Dividend declared
Subsequent Event [Line Items]
Dividends declared per common share (in dollars per share)				$ 0.13
Subsequent event | Dividend declared
Subsequent Event [Line Items]
Dividends declared per common share (in dollars per share)					$ 0.13
Subsequent event | Dividend declared | Preference Shares - Series A
Subsequent Event [Line Items]
Dividends declared per Preference share (in dollars per share)					$ 0.515625
Subsequent event | Dividend declared | Preference shares - Series B
Subsequent Event [Line Items]
Dividends declared per Preference share (in dollars per share)					$ 0.90625