Retirement Plans - Net Pension Expense Domestic and Foreign (Details) - Pension Plans - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Net pension expense (income)
Total expense, net	$ 1,957	$ 664
UNITED STATES
Net pension expense (income)
Service cost	0	0
Interest cost	1,253	1,443
Expected return on plan assets	(1,113)	(2,454)
Amortization of loss	1,767	1,622
Total expense, net	1,907	611
Foreign Plan
Net pension expense (income)
Service cost	6	7
Interest cost	4	7
Expected return on plan assets	(3)	(4)
Amortization of loss	43	43
Total expense, net	$ 50	$ 53