Earnings Per Share (Schedule Of Earnings Per Share) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Earnings Per Share [Abstract]
Net Income (Loss) Attributable to Parent	$ (2,401)	$ 261,813	$ (483,701)	$ 711,783
Participating securities’ (restricted stock) share in earnings	0	385	0	1,033
Net income (loss) attributable to common shares	$ (2,401)	$ 261,428	$ (483,701)	$ 710,750
Average number of shares of common stock outstanding	162,015	163,676	161,927	167,935
Effect of dilutive variable restricted stock units and performance share units	0	1,335	0	1,190
Average number of shares of common stock outstanding assuming dilution	162,015	165,011	161,927	169,125
Basic earnings (loss) per share	$ (0.01)	$ 1.60	$ (2.99)	$ 4.23
Diluted earnings (loss) per share	$ (0.01)	$ 1.58	$ (2.99)	$ 4.20
Excludes anti-dilutive restricted and performance share units of:	566	109	550	120