Earnings Per Share (Schedule Of Computation Of Earnings Per Share) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Earnings Per Share[Abstract]
Earnings	$ 56,522	$ 82,101	$ 121,922	$ 137,992
Diluted earnings	$ 56,522	$ 82,101	$ 121,922	$ 137,992
Earnings, Shares	15,829	15,914	15,919	15,953
Dilutive stock options, Shares	235	383	242	415
Nonvested stock awards, Shares	37	76	44	77
Diluted earnings, Shares	16,101	16,373	16,205	16,445
Earnings, Earnings per Share	$ 3.57	$ 5.16	$ 7.66	$ 8.65
Diluted earnings, Earnings per Share	$ 3.51	$ 5.01	$ 7.52	$ 8.39