Earnings Per Share (Schedule Of Earnings Per Share) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Earnings Per Share [Abstract]
Net Income (Loss) Attributable to Parent	$ 141,896	$ 342,466	$ 345,507	$ 268,091	$ 521,082	$ 272,014	$ 57,767	$ (45,468)	$ 1,097,960	$ 805,395	$ (260,453)
Participating securities' (restricted stock) share in earnings									3,714	5,047	1,003
Net income (loss) attributable to common shares									$ 1,094,246	$ 800,348	$ (261,456)
Average number of shares of common stock outstanding	172,485	175,097	175,899	176,617	176,265	176,149	176,147	176,210	175,009	176,174	176,101
Effect of dilutive variable restricted shares and performance share units									1,652	1,022	0
Average number of shares of common stock outstanding assuming dilution	174,259	176,927	177,586	177,954	177,457	176,530	176,302	176,210	176,661	177,196	176,101
Basic earnings (loss) per share	$ 0.82	$ 1.95	$ 1.96	$ 1.51	$ 2.94	$ 1.53	$ 0.33	$ (0.26)	$ 6.25	$ 4.54	$ (1.48)
Diluted earnings (loss) per share	$ 0.81	$ 1.93	$ 1.94	$ 1.50	$ 2.92	$ 1.53	$ 0.33	$ (0.26)	$ 6.19	$ 4.52	$ (1.48)
Excludes anti-dilutive restricted and performance share units									238	543	469