Post-retirement Plan (Net Periodic Pension Expense) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Service Cost	$ 1,117	$ 1,027
Interest cost on projected benefit obligations	437	598
Expected return on plan assets	(1,021)	(811)
Net periodic pension expense	533	814
Other Postretirement Benefits Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Service Cost	451	367
Interest cost on projected benefit obligations	237	258
Amortization of prior service credit	(870)	(870)
Amortization of (gain) loss	13	(20)
Net periodic post-retirement credit	$ (169)	$ (265)