Benefit Plans - Net Periodic Benefit Cost (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Defined Benefit Pension Plans | United States
Defined Benefit Plan, Net Periodic Benefit Cost (Credit)
Service cost	$ 769	$ 978	$ 1,019
Interest cost	8,595	10,281	9,599
Expected return on plan assets	(12,547)	(11,508)	(12,851)
Amortization of prior service cost	0	0	0
Amortization of net (gain) loss	0	0	0
Curtailment gain recognized	0	0	(576)
Settlement (gain) loss recognized	78	49	0
Net periodic expense (benefit)	(3,105)	(200)	(2,809)
Defined Benefit Pension Plans | Foreign
Defined Benefit Plan, Net Periodic Benefit Cost (Credit)
Service cost	3,895	3,210	3,104
Interest cost	2,193	2,627	2,637
Expected return on plan assets	(2,270)	(2,427)	(2,490)
Amortization of prior service cost	0	24	0
Amortization of net (gain) loss	148	(29)	49
Curtailment gain recognized	0	0	0
Settlement (gain) loss recognized	(14)	(1)	0
Net periodic expense (benefit)	3,952	3,404	3,300
Supplemental Retirement Plans
Defined Benefit Plan, Net Periodic Benefit Cost (Credit)
Interest cost	352	465	450
Amortization of net (gain) loss	0	(10)	0
Net periodic expense (benefit)	352	455	450
Other Postretirement Benefits Plans
Defined Benefit Plan, Net Periodic Benefit Cost (Credit)
Service cost	0	10	16
Interest cost	99	152	150
Amortization of prior service cost	(232)	(157)	(112)
Amortization of net (gain) loss	(29)	(33)	(26)
Net periodic expense (benefit)	$ (162)	$ (28)	$ 28