Employee Benefit Plans - Actuarial Assumptions (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Change in benefit obligation:
Beginning balance	$ (82,014)	$ (76,054)
Service cost	(66)	(78)
Interest cost	(2,420)	(2,907)
Actuarial gain (loss)	(6,903)	(7,557)
Benefits paid	2,459	4,440
Plan participants’ contributions	(19)	(12)
Foreign currency translation loss (gain)	(109)	2
Effect of settlement	1,266	152
Ending balance	(87,806)	(82,014)	$ (76,054)
Change in plan assets:
Beginning balance	69,308	59,737
Actual return on plan assets	9,981	11,597
Employer contributions	2,949	2,560
Benefits paid	(2,459)	(4,440)
Effect of settlement	(1,266)	(152)
Plan participants’ contributions	19	12
Foreign currency translation gain	129	(6)
Ending balance	78,661	69,308	59,737
Funded status	(9,145)	(12,706)
Amounts recognized on the consolidated balance sheet:
Pension and post-retirement liability	(9,145)	(12,706)
Accumulated other comprehensive loss (income)	9,586	10,959
Amounts in accumulated other comprehensive loss consist of:
Net loss	9,586	10,882
Prior service cost	53	77
Other changes in plan assets and benefit obligations recognized in other comprehensive (income) loss:
Net (gain) loss	342	(1,177)
Amortization of net gain	(1,624)	(2,069)
Amortization of prior service cost	(31)	(28)
Amount recognized due to special event	(134)	10
Foreign currency translation loss	14	(5)
Total recognized in other comprehensive (income) loss	(1,433)	(3,269)	901
Information for plans with accumulated benefit obligation in excess of plan assets:
Projected benefit obligation	87,806	82,014
Accumulated benefit obligation	87,679,000	81,900
Fair value of plan assets	78,661	69,308
Pension
Change in plan assets:
Beginning balance	69,308
Ending balance	78,661	69,308
Other Post-Retirement Benefits
Change in benefit obligation:
Beginning balance	(611)	(678)
Service cost	0	0
Interest cost	(14)	(23)
Actuarial gain (loss)	(27)	(62)
Benefits paid	5	0
Plan participants’ contributions	0	0
Foreign currency translation loss (gain)	0	0
Effect of settlement	0	152
Ending balance	(647)	(611)	(678)
Change in plan assets:
Beginning balance	0	0
Actual return on plan assets	0	0
Employer contributions	5	152
Benefits paid	(5)	0
Effect of settlement	0	(152)
Plan participants’ contributions	0	0
Foreign currency translation gain	0	0
Ending balance	0	0	0
Funded status	(647)	(611)
Amounts recognized on the consolidated balance sheet:
Pension and post-retirement liability	(647)	(611)
Accumulated other comprehensive loss (income)	6	(21)
Amounts in accumulated other comprehensive loss consist of:
Net loss	6	(21)
Prior service cost	0	0
Other changes in plan assets and benefit obligations recognized in other comprehensive (income) loss:
Net (gain) loss	(94)	(94)
Amortization of net gain	0	4
Amortization of prior service cost	0	0
Amount recognized due to special event	0	5
Foreign currency translation loss	0	0
Total recognized in other comprehensive (income) loss	(94)	(85)
Information for plans with accumulated benefit obligation in excess of plan assets:
Projected benefit obligation	647	611
Accumulated benefit obligation	647,000	611
Fair value of plan assets	0	0
Retirement Income Plan | Pension
Change in benefit obligation:
Beginning balance	(45,215)	(43,364)
Service cost	0	0
Interest cost	(1,261)	(1,590)
Actuarial gain (loss)	(3,657)	(3,251)
Benefits paid	1,358	2,990
Plan participants’ contributions	0	0
Foreign currency translation loss (gain)	0	0
Effect of settlement	1,266	0
Ending balance	(47,509)	(45,215)	(43,364)
Change in plan assets:
Beginning balance	40,111	34,958
Actual return on plan assets	5,903	6,804
Employer contributions	1,640	1,339
Benefits paid	(1,358)	(2,990)
Effect of settlement	(1,266)	0
Plan participants’ contributions	0	0
Foreign currency translation gain	0	0
Ending balance	45,030	40,111	34,958
Funded status	(2,479)	(5,104)
Amounts recognized on the consolidated balance sheet:
Pension and post-retirement liability	(2,479)	(5,104)
Accumulated other comprehensive loss (income)	5,021	6,417
Amounts in accumulated other comprehensive loss consist of:
Net loss	5,021	6,417
Prior service cost	0	0
Other changes in plan assets and benefit obligations recognized in other comprehensive (income) loss:
Net (gain) loss	(244)	(1,793)
Amortization of net gain	(1,017)	(1,509)
Amortization of prior service cost	0	0
Amount recognized due to special event	(134)	0
Foreign currency translation loss	0	0
Total recognized in other comprehensive (income) loss	(1,395)	(3,302)
Information for plans with accumulated benefit obligation in excess of plan assets:
Projected benefit obligation	47,509	45,215
Accumulated benefit obligation	47,508,000	45,215
Fair value of plan assets	45,030	40,111
National Service-Related Pension Plan | Pension
Change in benefit obligation:
Beginning balance	(35,036)	(30,627)
Service cost	0	0
Interest cost	(1,117)	(1,245)
Actuarial gain (loss)	(3,147)	(4,167)
Benefits paid	1,073	1,003
Plan participants’ contributions	0	0
Foreign currency translation loss (gain)	0	0
Effect of settlement	0	0
Ending balance	(38,227)	(35,036)	(30,627)
Change in plan assets:
Beginning balance	27,841	23,277
Actual return on plan assets	4,034	4,556
Employer contributions	1,259	1,011
Benefits paid	(1,073)	(1,003)
Effect of settlement	0	0
Plan participants’ contributions	0	0
Foreign currency translation gain	0	0
Ending balance	32,061	27,841	23,277
Funded status	(6,166)	(7,195)
Amounts recognized on the consolidated balance sheet:
Pension and post-retirement liability	(6,166)	(7,195)
Accumulated other comprehensive loss (income)	4,473	4,501
Amounts in accumulated other comprehensive loss consist of:
Net loss	4,473	4,501
Prior service cost	0	0
Other changes in plan assets and benefit obligations recognized in other comprehensive (income) loss:
Net (gain) loss	578	788
Amortization of net gain	(607)	(564)
Amortization of prior service cost	0	0
Amount recognized due to special event	0	0
Foreign currency translation loss	0	0
Total recognized in other comprehensive (income) loss	(29)	224
Information for plans with accumulated benefit obligation in excess of plan assets:
Projected benefit obligation	38,227	35,036
Accumulated benefit obligation	38,227,000	35,036
Fair value of plan assets	32,061	27,841
Superannuation | Pension
Change in benefit obligation:
Beginning balance	(1,152)	(1,385)
Service cost	(66)	(78)
Interest cost	(28)	(49)
Actuarial gain (loss)	(72)	(77)
Benefits paid	23	447
Plan participants’ contributions	(19)	(12)
Foreign currency translation loss (gain)	(109)	2
Effect of settlement	0	0
Ending balance	(1,423)	(1,152)	(1,385)
Change in plan assets:
Beginning balance	1,356	1,502
Actual return on plan assets	44	237
Employer contributions	45	58
Benefits paid	(23)	(447)
Effect of settlement	0	0
Plan participants’ contributions	19	12
Foreign currency translation gain	129	(6)
Ending balance	1,570	1,356	$ 1,502
Funded status	147	204
Amounts recognized on the consolidated balance sheet:
Pension and post-retirement liability	147	204
Accumulated other comprehensive loss (income)	86	62
Amounts in accumulated other comprehensive loss consist of:
Net loss	86	(15)
Prior service cost	53	77
Other changes in plan assets and benefit obligations recognized in other comprehensive (income) loss:
Net (gain) loss	102	(78)
Amortization of net gain	0	0
Amortization of prior service cost	(31)	(28)
Amount recognized due to special event	0	5
Foreign currency translation loss	14	(5)
Total recognized in other comprehensive (income) loss	85	(106)
Information for plans with accumulated benefit obligation in excess of plan assets:
Projected benefit obligation	1,423	1,152
Accumulated benefit obligation	1,297,000	1,038
Fair value of plan assets	$ 1,570	$ 1,356