Retirement Plans and Other Postretirement Benefits - Components of Net Periodic Benefit Cost (Income) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Retirement Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 109	$ 140
Interest cost	476	441
Expected return on plan assets	(771)	(796)
Amortization of net actuarial loss	294	280
Accretion of prior service cost	(45)	(71)
Net periodic benefit cost (income)	63	(6)
Other Post Retirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	17	22
Interest cost	23	23
Expected return on plan assets	0	0
Amortization of net actuarial loss	0	1
Accretion of prior service cost	0	0
Net periodic benefit cost (income)	$ 40	$ 46