Shareholders' Equity (Changes in Shares by Class) (Details) - shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance, Common stock, shares outstanding	122,266,106
Stock options exercised	197,631	297,225	338,808
Repurchase of common stock	4,000,000
Balance, Common stock, shares outstanding	118,897,295	122,266,106
Preferred Shares Issued | Series C Preferred Stock
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance	5,200,000	5,200,000	5,200,000
Issuance of common stock	0	0
Restricted share unit activity	0	0	0
Stock options exercised	0	0	0
Balance	5,200,000	5,200,000	5,200,000
Common Stock
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance	142,026,000	140,592,000	139,950,000
Balance, Common stock, shares outstanding	122,266,000	129,547,000	136,123,000
Issuance of common stock	118,000	821,000
Restricted share unit activity	336,000	316,000	304,000
Stock options exercised	198,000	297,000	338,000
Repurchase of common stock	(4,021,000)	(8,715,000)	(7,218,000)
Balance	142,678,000	142,026,000	140,592,000
Balance, Common stock, shares outstanding	118,897,000	122,266,000	129,547,000
Treasury Stock
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance	19,760,000	11,045,000	3,827,000
Issuance of common stock	0	0
Restricted share unit activity	0	0	0
Stock options exercised	0	0	0
Repurchase of common stock	4,021,000	8,715,000	7,218,000
Balance	23,781,000	19,760,000	11,045,000