Employee Benefit Plans - Actuarial Assumptions (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Change in benefit obligation:
Beginning balance	$ (76,054)	$ (82,484)
Service cost	(78)	(246)	$ (722)
Interest cost	(2,907)	(2,741)	(2,981)
Actuarial gain (loss)	(7,557)	4,090
Benefits paid	4,440	5,039
Plan participants’ contributions	(12)	(21)
Foreign currency translation loss (gain)	2	309
Effect of settlement	152
Ending balance	(82,014)	(76,054)	(82,484)
Change in plan assets:
Beginning balance	59,737	65,728
Actual return on plan assets	11,597	(3,438)
Employer contributions	2,560	2,759
Benefits paid	(4,440)	(5,038)
Effect of settlement	(152)
Plan participants’ contributions	12	21
Foreign currency translation loss	(6)	(295)
Ending balance	69,308	59,737	65,728
Funded status	(12,706)	(16,317)
Amounts recognized on the consolidated balance sheet:
Pension and post-retirement liability	(12,706)	(16,317)
Accumulated other comprehensive loss (income)	10,959	14,074
Amounts in accumulated other comprehensive loss consist of:
Net loss (gain)	10,882	13,969
Prior service cost	77	105
Other changes in plan assets and benefit obligations recognized in other comprehensive income (loss):
Net (gain) loss	(1,177)	2,926
Amortization of net (loss) gain	(2,069)	(1,959)
Amortization of prior service cost	(28)	(28)
Amount recognized due to special event	10	(64)
Foreign currency translation loss	(5)	26
Total recognized in other comprehensive loss (income)	(3,269)	901	(5,754)
Information for plans with accumulated benefit obligation in excess of plan assets:
Projected benefit obligation	82,014	76,054
Accumulated benefit obligation	81,900	75,855
Fair value of plan assets	69,308	59,737
Pension
Change in plan assets:
Beginning balance	59,737
Ending balance	69,308	59,737
Other Post-Retirement Benefits
Change in benefit obligation:
Beginning balance	(678)	(691)
Service cost	0	0	0
Interest cost	(23)	(20)	(22)
Actuarial gain (loss)	(62)	33
Benefits paid	0	0
Plan participants’ contributions	0	0
Foreign currency translation loss (gain)	0	0
Effect of settlement	152
Ending balance	(611)	(678)	(691)
Change in plan assets:
Beginning balance	0	0
Actual return on plan assets	0	0
Employer contributions	152	0
Benefits paid	0	0
Effect of settlement	(152)
Plan participants’ contributions	0	0
Foreign currency translation loss	0	0
Ending balance	0	0	0
Funded status	(611)	(678)
Amounts recognized on the consolidated balance sheet:
Pension and post-retirement liability	(611)	(678)
Accumulated other comprehensive loss (income)	(21)	(92)
Amounts in accumulated other comprehensive loss consist of:
Net loss (gain)	(21)	(92)
Prior service cost	0	0
Other changes in plan assets and benefit obligations recognized in other comprehensive income (loss):
Net (gain) loss	(94)	(34)
Amortization of net (loss) gain	4	0
Amortization of prior service cost	0	0
Amount recognized due to special event	5	0
Foreign currency translation loss	0	0
Total recognized in other comprehensive loss (income)	(85)	(34)
Information for plans with accumulated benefit obligation in excess of plan assets:
Projected benefit obligation	611	678
Accumulated benefit obligation	611	678
Fair value of plan assets	0	0
Retirement Income Plan | Pension
Change in benefit obligation:
Beginning balance	(43,364)	(45,386)
Service cost	0	(31)	(65)
Interest cost	(1,590)	(1,418)	(1,583)
Actuarial gain (loss)	(3,251)	753
Benefits paid	2,990	2,718
Plan participants’ contributions	0	0
Foreign currency translation loss (gain)	0	0
Effect of settlement	0
Ending balance	(45,215)	(43,364)	(45,386)
Change in plan assets:
Beginning balance	34,958	38,218
Actual return on plan assets	6,804	(2,042)
Employer contributions	1,339	1,499
Benefits paid	(2,990)	(2,717)
Effect of settlement	0
Plan participants’ contributions	0	0
Foreign currency translation loss	0	0
Ending balance	40,111	34,958	38,218
Funded status	(5,104)	(8,406)
Amounts recognized on the consolidated balance sheet:
Pension and post-retirement liability	(5,104)	(8,406)
Accumulated other comprehensive loss (income)	6,417	9,718
Amounts in accumulated other comprehensive loss consist of:
Net loss (gain)	6,417	9,718
Prior service cost	0	0
Other changes in plan assets and benefit obligations recognized in other comprehensive income (loss):
Net (gain) loss	(1,793)	3,337
Amortization of net (loss) gain	(1,509)	(1,244)
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 loss (income)	(3,302)	2,093
Information for plans with accumulated benefit obligation in excess of plan assets:
Projected benefit obligation	45,215	43,364
Accumulated benefit obligation	45,215	43,364
Fair value of plan assets	40,111	34,958
National Service-Related Pension Plan | Pension
Change in benefit obligation:
Beginning balance	(30,627)	(33,405)
Service cost	0	(78)	(504)
Interest cost	(1,245)	(1,199)	(1,256)
Actuarial gain (loss)	(4,167)	3,125
Benefits paid	1,003	930
Plan participants’ contributions	0	0
Foreign currency translation loss (gain)	0	0
Effect of settlement	0
Ending balance	(35,036)	(30,627)	(33,405)
Change in plan assets:
Beginning balance	23,277	24,518
Actual return on plan assets	4,556	(1,446)
Employer contributions	1,011	1,135
Benefits paid	(1,003)	(930)
Effect of settlement	0
Plan participants’ contributions	0	0
Foreign currency translation loss	0	0
Ending balance	27,841	23,277	24,518
Funded status	(7,195)	(7,350)
Amounts recognized on the consolidated balance sheet:
Pension and post-retirement liability	(7,195)	(7,350)
Accumulated other comprehensive loss (income)	4,501	4,278
Amounts in accumulated other comprehensive loss consist of:
Net loss (gain)	4,501	4,278
Prior service cost	0	0
Other changes in plan assets and benefit obligations recognized in other comprehensive income (loss):
Net (gain) loss	788	(311)
Amortization of net (loss) gain	(564)	(715)
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 loss (income)	224	(1,026)
Information for plans with accumulated benefit obligation in excess of plan assets:
Projected benefit obligation	35,036	30,627
Accumulated benefit obligation	35,036	30,627
Fair value of plan assets	27,841	23,277
Superannuation | Pension
Change in benefit obligation:
Beginning balance	(1,385)	(3,002)
Service cost	(78)	(137)	(153)
Interest cost	(49)	(104)	(120)
Actuarial gain (loss)	(77)	179
Benefits paid	447	1,391
Plan participants’ contributions	(12)	(21)
Foreign currency translation loss (gain)	2	309
Effect of settlement	0
Ending balance	(1,152)	(1,385)	(3,002)
Change in plan assets:
Beginning balance	1,502	2,992
Actual return on plan assets	237	50
Employer contributions	58	125
Benefits paid	(447)	(1,391)
Effect of settlement	0
Plan participants’ contributions	12	21
Foreign currency translation loss	(6)	(295)
Ending balance	1,356	1,502	$ 2,992
Funded status	204	117
Amounts recognized on the consolidated balance sheet:
Pension and post-retirement liability	204	117
Accumulated other comprehensive loss (income)	62	170
Amounts in accumulated other comprehensive loss consist of:
Net loss (gain)	(15)	65
Prior service cost	77	105
Other changes in plan assets and benefit obligations recognized in other comprehensive income (loss):
Net (gain) loss	(78)	(66)
Amortization of net (loss) gain	0	0
Amortization of prior service cost	(28)	(28)
Amount recognized due to special event	5	(64)
Foreign currency translation loss	(5)	26
Total recognized in other comprehensive loss (income)	(106)	(132)
Information for plans with accumulated benefit obligation in excess of plan assets:
Projected benefit obligation	1,152	1,385
Accumulated benefit obligation	1,038	1,186
Fair value of plan assets	$ 1,356	$ 1,502