Employee Benefit and Deferred Compensation Plans - Plan Expense for Non-Contributory Benefit Pension Plan and Post-Retirement Health and Life Plans (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Pension Benefits
Plan expense for noncontributory benefit pension plan and post-retirement health and life plans
Service cost	$ 0	$ 0	$ 0	$ 0
Interest cost	171	246	512	738
Expected return on plan assets	(442)	(412)	(1,326)	(1,238)
Recognized actuarial loss (gain)	67	87	199	262
Net periodic (return) benefit cost	(204)	(79)	(615)	(238)
Other Benefits
Plan expense for noncontributory benefit pension plan and post-retirement health and life plans
Service cost	2	2	4	5
Interest cost	4	3	11	10
Expected return on plan assets	0	0	0	0
Recognized actuarial loss (gain)	0	(23)	(2)	(68)
Net periodic (return) benefit cost	$ 6	$ (18)	$ 13	$ (53)