Employee Benefit Plans - Components of Net Period Benefit Cost (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 78	$ 246	$ 722
Interest cost	2,907	2,741	2,981
Expected return on plan assets	(3,010)	(3,588)	(3,106)
Amortization of net loss (gain)	2,069	1,959	2,703
Amortization of prior service cost	28	30	221
Effect of settlement	(10)	68	63
Net pension benefit cost	2,062	1,456	3,584
Pension | Retirement Income Plan
Defined Benefit Plan Disclosure [Line Items]
Service cost	0	31	65
Interest cost	1,590	1,418	1,583
Expected return on plan assets	(1,760)	(2,047)	(1,757)
Amortization of net loss (gain)	1,509	1,244	1,889
Amortization of prior service cost	0	0	0
Effect of settlement	0	0	0
Net pension benefit cost	1,339	646	1,780
Pension | National Service-Related Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Service cost	0	78	504
Interest cost	1,245	1,199	1,256
Expected return on plan assets	(1,176)	(1,369)	(1,175)
Amortization of net loss (gain)	564	715	815
Amortization of prior service cost	0	0	212
Effect of settlement	0	0	0
Net pension benefit cost	633	623	1,612
Pension | Superannuation
Defined Benefit Plan Disclosure [Line Items]
Service cost	78	137	153
Interest cost	49	104	120
Expected return on plan assets	(74)	(172)	(174)
Amortization of net loss (gain)	0	0	0
Amortization of prior service cost	28	30	9
Effect of settlement	(5)	68	67
Net pension benefit cost	76	167	175
Other Post-Retirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	0	0	0
Interest cost	23	20	22
Expected return on plan assets	0	0	0
Amortization of net loss (gain)	(4)	0	(1)
Amortization of prior service cost	0	0	0
Effect of settlement	(5)	0	(4)
Net pension benefit cost	$ 14	$ 20	$ 17