Post-retirement Plan (Net Periodic Pension Expense) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Service Cost	$ 1,027	$ 1,104
Interest cost on projected benefit obligations	598	562
Expected return on plan assets	(811)	(865)
Net periodic pension expense	814	801
Other Postretirement Benefits Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Service Cost	367	412
Interest cost on projected benefit obligations	258	234
Amortization of prior service credit	(870)	(870)
Defined Benefit Plan, Amortization of Gain (Loss)	(20)	0
Net periodic post-retirement credit	$ (265)	$ (224)