Retirement Plans - Other Postretirement Benefit Plan (Details) - Other Postretirement Benefits Plan - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 1	$ 0	$ 1	$ 1
Interest cost	30	42	90	127
Amortization of gain	(20)	(42)	(64)	(125)
Total expense, net	$ 11	$ 0	$ 27	$ 3