Retirement Plans - Other Postretirement Benefit Plan (Details) - Other Postretirement Benefits Plan - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 0	$ 0	$ 0	$ 0
Interest cost	20	30	43	60
Amortization of gain	0	(21)	0	(42)
Total expense, net	$ 20	$ 9	$ 43	$ 18