Retirement Plans - Other Postretirement Benefit Plan (Details) - Other Postretirement Benefits Plan - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 0	$ 1	$ 0	$ 1
Interest cost	20	30	63	90
Amortization of gain	0	(20)	0	(64)
Total expense, net	$ 20	$ 11	$ 63	$ 27