Defined Pension Plans (Schedule of Net Periodic Pension Costs) (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018
Defined Benefit Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost - benefits earned during the year	$ 3,708	$ 4,017
Interest cost on projected benefit obligation	4,083	3,703
Expected return on plan assets	(4,754)	(5,202)
Net amortization	1,634	1,522
Net periodic pension cost	4,671	4,040
Unfunded Supplemental Executive Retirement Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost - benefits earned during the year	97	92
Interest cost on projected benefit obligation	408	348
Net amortization	276	581
Net periodic pension cost	$ 781	$ 1,021