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, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Retirement Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 116	$ 110	$ 233	$ 219
Interest cost	417	476	834	952
Expected return on plan assets	(818)	(770)	(1,634)	(1,541)
Amortization of net actuarial loss	291	294	582	588
Accretion of prior service cost	0	(46)	0	(91)
Net periodic benefit cost	6	64	15	127
Other Post Retirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	27	16	55	33
Interest cost	25	24	49	47
Expected return on plan assets	0	0	0	0
Amortization of net actuarial loss	6	0	12	0
Accretion of prior service cost	0	0	0	0
Net periodic benefit cost	$ 58	$ 40	$ 116	$ 80