Retirement Plans - Other Postretirement Benefit Plan (Details) - Other Postretirement Benefits Plan [Member] - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Defined Benefit Plan Disclosure
Service cost	$ 1	$ 0	$ 1	$ 1
Interest cost	43	39	85	78
Amortization of gain	(42)	(11)	(83)	(23)
(Income) expense, net	$ 2	$ 28	$ 3	$ 56