Shareholders' Equity (Shares Issued and Outstanding) (Details) - shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares issued - January 1 (in shares)	41,187,413
Shares outstanding - January 1 (in shares)	41,187,413
Shares issued - December 31 (in shares)	40,023,789	41,187,413
Shares outstanding - December 31 (in shares)	40,023,789	41,187,413
Common shares
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares issued - January 1 (in shares)	41,187,000	43,701,000	38,442,000
Shares outstanding - January 1 (in shares)	41,187,000	43,701,000	38,442,000
Issuance of shares (in shares)	0	0	7,435,000
Repurchase of shares (in shares)	(1,322,000)	(2,741,000)	(2,473,000)
Exercise of options and issuance of restricted stock awards (in shares)	159,000	227,000	297,000
Shares issued - December 31 (in shares)	40,024,000	41,187,000	43,701,000
Shares outstanding - December 31 (in shares)	40,024,000	41,187,000	43,701,000