Shareholders' Equity (Details) - USD ($) $ / shares in Units, shares in Millions					3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 15, 2016	Mar. 31, 2016	Mar. 15, 2016	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015	May 16, 2016
Class of Stock [Line Items]
Dividends declared per common share (in usd per share)					$ 0.31	$ 0.30	$ 0.62	$ 0.6
Dividends declared and paid, Preference shares					$ 5,596,000	$ 5,596,000	$ 11,191,000	$ 11,191,000
Retained Earnings
Class of Stock [Line Items]
Dividends declared and paid, Preference shares							11,191,000	11,191,000
Dividends declared and paid, Common shares							$ 26,198,000	$ 27,479,000
Common Shares
Class of Stock [Line Items]
Dividends declared per common share (in usd per share)		$ 0.31		$ 0.31
Dividends paid per common share	$ 0.31		$ 0.31
Share repurchase program, Authorized amount									$ 500,000,000
Common shares repurchased during period, Number of shares							2.4
Common shares repurchased during period, Aggregate amount							$ 272,300,000
Common shares repurchased during period, Average cost per share, in usd per share							$ 112.50
Share repurchase program, Remaining authorized aggregate amount	$ 397,100,000				$ 397,100,000		$ 397,100,000