Employee Benefit Plans - Components of Net Period Benefit Cost (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 15	$ 18	$ 47	$ 46
Interest cost	477	606	1,433	1,815
Expected return on plan assets	(1,042)	(886)	(3,126)	(2,651)
Amortization of net loss	382	407	1,144	1,218
Amortization of prior service cost	7	7	22	22
Net pension benefit cost	(161)	152	(480)	450
Pension | Retirement Income Plan
Defined Benefit Plan Disclosure [Line Items]
Service cost	0	0	0	0
Interest cost	236	315	710	946
Expected return on plan assets	(596)	(500)	(1,788)	(1,501)
Amortization of net loss	219	255	655	763
Amortization of prior service cost	0	0	0	0
Net pension benefit cost	(141)	70	(423)	208
Pension | National Service-Related Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Service cost	0	0	0	0
Interest cost	234	279	702	838
Expected return on plan assets	(428)	(366)	(1,282)	(1,099)
Amortization of net loss	163	152	489	455
Amortization of prior service cost	0	0	0	0
Net pension benefit cost	(31)	65	(91)	194
Pension | Superannuation
Defined Benefit Plan Disclosure [Line Items]
Service cost	15	18	47	46
Interest cost	5	8	15	20
Expected return on plan assets	(18)	(20)	(56)	(51)
Amortization of net loss	0	0	0	0
Amortization of prior service cost	7	7	22	22
Net pension benefit cost	9	13	28	37
Other Post-Retirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	0	0	0	0
Interest cost	2	4	6	11
Expected return on plan assets	0	0	0	0
Amortization of net loss	0	0	0	0
Amortization of prior service cost	0	0	0	0
Net pension benefit cost	$ 2	$ 4	$ 6	$ 11