Earnings (Loss) Per Common Share (Computation Of Basic And Diluted Earnings Per Common Share) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended							9 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2020	Sep. 30, 2019
Earnings Per Share [Abstract]
Net (loss) income	$ 124,871	$ 52,926	$ (1,851,947)	$ 83,750	$ 84,502	$ 111,810	$ 74,033	$ (1,674,150)	$ 270,345
Weighted average number of common shares outstanding - basic (in shares)	220,221				220,285			220,216	220,379
Effect of potentially dilutive common shares (in shares)	197				298			0	263
Weighted average number of shares outstanding, diluted (in shares)	220,418				220,583			220,216	220,642
EARNINGS (LOSS) PER COMMON SHARE:
Basic (in dollars per share)	$ 0.57				$ 0.38			$ (7.60)	$ 1.23
Diluted (in dollars per share)	$ 0.57				$ 0.38			$ (7.60)	$ 1.23