Benefit Plan (Components Of Net Periodic Benefit Expense) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Defined Benefit Plan Disclosure [Line Items]
Pension plan contributions	$ 0	$ 0
Service cost	2,479	2,080
Interest cost	1,340	1,320
Defined Benefit Plan, Net Periodic Benefit Cost (Credit)	441	92
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Service cost	2,479	2,080
Interest cost	1,340	1,320
Expected return on plan assets	(3,933)	(3,602)
Recognized net actuarial loss	555	294
Benefit expense	441	92
Supplemental Employee Retirement Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	204	364
Interest cost	149	134
Defined Benefit Plan, Net Periodic Benefit Cost (Credit)	353	498
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Service cost	204	364
Interest cost	149	134
Benefit expense	$ 353	$ 498