Earnings per Share (Reconciliation Of Denominator For Basic And Diluted Earnings (Loss) Per Share) (Details) - $ / shares	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Earnings Per Share [Abstract]
Weighted average common shares—basic									129,087,043	129,367,712	131,823,707
Plus incremental shares from: Assumed exercise of options									452,970	607,110	478,105
Weighted average common shares—diluted									129,540,013	129,974,822	132,301,812
Basic (in dollars per share)	$ 6.18	$ 1.62	$ 1.18	$ 1.07	$ 0.76	$ 0.51	$ 0.85	$ 0.94	$ 10.05	$ 3.07	$ 4.88
Diluted (in dollars per share)	$ 6.15	$ 1.61	$ 1.17	$ 1.06	$ 0.76	$ 0.51	$ 0.85	$ 0.94	$ 10.00	$ 3.06	$ 4.86