Retirement Plans and Other Postretirement Benefits - Components of Net Periodic Benefit Cost (Income) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Retirement Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 117	$ 109
Interest cost	417	476
Expected return on plan assets	(816)	(771)
Amortization of net actuarial loss	291	294
Accretion of prior service cost	0	(45)
Net periodic benefit cost	9	63
Other Post Retirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	28	17
Interest cost	24	23
Expected return on plan assets	0	0
Amortization of net actuarial loss	6	0
Accretion of prior service cost	0	0
Net periodic benefit cost	$ 58	$ 40