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, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Pension Benefits
Plan expense for noncontributory benefit pension plan and post-retirement health and life plans
Service cost	$ 0	$ 0	$ 0	$ 0
Interest cost	246	294	738	882
Expected return on plan assets	(412)	(362)	(1,238)	(1,087)
Recognized actuarial loss (gain)	87	110	262	331
Net periodic (return) benefit cost	(79)	42	(238)	126
Other Benefits
Plan expense for noncontributory benefit pension plan and post-retirement health and life plans
Service cost	2	2	5	5
Interest cost	3	7	10	23
Expected return on plan assets	0	0	0	0
Recognized actuarial loss (gain)	(23)	(6)	(68)	(17)
Net periodic (return) benefit cost	$ (18)	$ 3	$ (53)	$ 11