Earnings 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, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Sep. 30, 2019	Sep. 30, 2018
Earnings Per Share [Abstract]
Net income	$ 84,502	$ 111,810	$ 74,033	$ 80,311	$ 90,981	$ 65,999	$ 78,972	$ 270,345	$ 235,952
Weighted average number of common shares outstanding - basic (in shares)	220,285				220,224			220,379	220,292
Effect of potentially dilutive common shares (in shares)	298				396			263	459
Weighted average number of shares outstanding, diluted (in shares)	220,583				220,620			220,642	220,751
EARNINGS PER COMMON SHARE:
Basic (in dollars per share)	$ 0.38				$ 0.41			$ 1.23	$ 1.07
Diluted (in dollars per share)	$ 0.38				$ 0.41			$ 1.23	$ 1.07