Post-retirement Plan (Net Periodic Pension Expense) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Defined Benefit Plan Disclosure [Line Items]
Service cost - benefit earned during the period	$ 1,117	$ 1,209	$ 3,321	$ 3,605
Interest cost on projected benefit obligations	428	450	1,287	1,325
Expected return on plan assets	(1,016)	(822)	(3,029)	(2,441)
Amortization of (gain) loss	0	15	0	45
Net periodic pension expense	529	852	1,579	2,534
Other Postretirement Benefits Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost - benefit earned during the period	451	387	1,352	1,161
Interest cost on projected benefit obligations	237	267	710	801
Amortization of prior service credit	(870)	(870)	(2,611)	(2,611)
Amortization of (gain) loss	13	(22)	38	(66)
Net periodic post-retirement credit	$ (169)	$ (238)	$ (511)	$ (715)