Per Share Data (Calculation Of Basic And Diluted Earnings Per Share) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Earnings Per Share [Abstract]
Number of common share equivalent securities excluded from the diluted earnings per share calculation	1,400	2,400	1,500	2,500
Income from continuing operations attributable to common shareholders	$ 34,384	$ 290,898	$ 108,433	$ 396,088
Amount allocated to participating securities	(21)	(1,625)	(133)	(6,142)
Income from continuing operations attributable to common shareholders, net of amount allocated to participating securities	34,363	289,273	108,300	389,946
Income from discontinued operations, including gain on sale, attributable to common shareholders	0	0	0	382,842
Net income attributable to common shareholders – basic	$ 34,363	$ 289,273	$ 108,300	$ 772,788
Earnings per common share from continuing operations	$ 0.38	$ 3.23	$ 1.20	$ 4.35
Earnings per common share from discontinued operations	0.00	0.00	0.00	4.28
Total earnings per common share – basic	$ 0.38	$ 3.23	$ 1.20	$ 8.63
Income allocated to common units from continuing operations	$ 294	$ 0	$ 869	$ 0
Income from continuing operations attributable to common shareholders, as adjusted	34,657	289,273	109,169	389,946
Net income attributable to common shareholders – diluted	$ 34,657	$ 289,273	$ 109,169	$ 772,788
Earnings per common share from continuing operations	$ 0.38	$ 3.21	$ 1.20	$ 4.34
Earnings per common share from discontinued operations	0.00	0.00	0.00	4.26
Total earnings per common share – diluted	$ 0.38	$ 3.21	$ 1.20	$ 8.60
Weighted average number of common shares outstanding – basic	91,011	89,669	90,351	89,524
Common share options and share awards granted	217	343	189	334
Common units	805	0	805	0
Weighted average number of common shares outstanding – diluted	92,033	90,012	91,345	89,858