Retirement Plans and Other Postretirement Benefits - Components of Net Periodic Benefit Cost (Income) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Retirement Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 130	$ 117
Interest cost	354	417
Expected loss on plan assets	(892)	(816)
Amortization of net actuarial loss	317	291
Net periodic benefit (income) cost	(91)	9
Other Post Retirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	36	28
Interest cost	21	24
Expected loss on plan assets	0	0
Amortization of net actuarial loss	12	6
Net periodic benefit (income) cost	$ 69	$ 58