Defined Pension Plans (Schedule of Net Periodic Pension Costs) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Defined Benefit Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost - benefits earned during the year	$ 963	$ 4,329
Interest cost on projected benefit obligations	3,069	3,908
Expected return on plan assets	(6,299)	(6,049)
Net amortization	360	1,946
Net periodic pension (benefit) cost	(1,907)	4,134
Unfunded Supplemental Executive Retirement Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost - benefits earned during the year	147	121
Interest cost on projected benefit obligations	291	347
Net amortization	203	112
Net periodic pension (benefit) cost	$ 641	$ 580