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		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 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	175	250	341	492
Expected return on plan assets	(441)	(413)	(884)	(826)
Recognized actuarial loss (gain)	78	96	132	175
Net periodic (return) benefit cost	(188)	(67)	(411)	(159)
Other Benefits
Plan expense for noncontributory benefit pension plan and post-retirement health and life plans
Service cost	1	1	2	3
Interest cost	3	2	7	7
Expected return on plan assets	0	0	0	0
Recognized actuarial loss (gain)	(2)	(27)	(2)	(45)
Net periodic (return) benefit cost	$ 2	$ (24)	$ 7	$ (35)