Employee Benefit Plans - Components of Net Period Benefit Cost (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 14	$ 20
Interest cost	604	727
Expected return on plan assets	(882)	(753)
Amortization of net loss	406	517
Amortization of prior service cost	8	7
Net pension benefit cost	150	518
Other Post-Retirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	0	0
Interest cost	4	6
Expected return on plan assets	0	0
Amortization of net loss	0	(1)
Amortization of prior service cost	0	0
Net pension benefit cost	4	5
Retirement Income Plan | Pension
Defined Benefit Plan Disclosure [Line Items]
Service cost	0	0
Interest cost	315	397
Expected return on plan assets	(500)	(440)
Amortization of net loss	254	377
Amortization of prior service cost	0	0
Net pension benefit cost	69	334
National Service-Related Pension Plan | Pension
Defined Benefit Plan Disclosure [Line Items]
Service cost	0	0
Interest cost	279	311
Expected return on plan assets	(366)	(294)
Amortization of net loss	152	141
Amortization of prior service cost	0	0
Net pension benefit cost	65	158
Superannuation | Pension
Defined Benefit Plan Disclosure [Line Items]
Service cost	14	20
Interest cost	6	13
Expected return on plan assets	(16)	(19)
Amortization of net loss	0	0
Amortization of prior service cost	8	7
Net pension benefit cost	$ 12	$ 21