Retirement Plans and Other Postretirement Benefits - Components of Net Periodic Benefit Cost (Income) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Retirement Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 164	$ 117	$ 425	$ 350
Interest cost	366	425	1,073	1,259
Expected return on plan assets	(946)	(816)	(2,739)	(2,450)
Amortization of net actuarial loss	318	300	952	882
Net periodic benefit (income) cost	(98)	26	(289)	41
Other Post Retirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	36	27	107	82
Interest cost	21	23	64	72
Expected return on plan assets	0	0	0	0
Amortization of net actuarial loss	11	7	35	19
Net periodic benefit (income) cost	$ 68	$ 57	$ 206	$ 173