Retirement Plans and Other Postretirement Benefits - Components of Net Periodic Benefit Cost (Income) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Retirement Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 131	$ 116	$ 261	$ 233
Interest cost	353	417	707	834
Expected loss on plan assets	(901)	(818)	(1,793)	(1,634)
Amortization of net actuarial loss	317	291	634	582
Net periodic benefit (income) cost	(100)	6	(191)	15
Other Post Retirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	35	27	71	55
Interest cost	22	25	43	49
Expected loss on plan assets	0	0	0	0
Amortization of net actuarial loss	12	6	24	12
Net periodic benefit (income) cost	$ 69	$ 58	$ 138	$ 116