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
	Mar. 31, 2021	Mar. 31, 2020
Pension Benefits
Plan expense for noncontributory benefit pension plan and post-retirement health and life plans
Service cost	$ 0	$ 0
Interest cost	166	242
Expected return on plan assets	(443)	(413)
Recognized actuarial loss (gain)	54	79
Net periodic (return) benefit cost	(223)	(92)
Other Benefits
Plan expense for noncontributory benefit pension plan and post-retirement health and life plans
Service cost	1	2
Interest cost	4	5
Expected return on plan assets	0	0
Recognized actuarial loss (gain)	0	(18)
Net periodic (return) benefit cost	$ 5	$ (11)