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, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Pension Benefits
Plan expense for noncontributory benefit pension plan and post-retirement health and life plans
Service cost	$ 0	$ 0	$ 0	$ 0
Interest cost	294	261	882	783
Expected return on plan assets	(362)	(520)	(1,087)	(1,558)
Recognized actuarial loss (gain)	110	82	331	246
Net periodic benefit cost (return)	42	(177)	126	(529)
Other Benefits
Plan expense for noncontributory benefit pension plan and post-retirement health and life plans
Service cost	2	2	5	6
Interest cost	7	7	23	23
Expected return on plan assets	0	0	0	0
Recognized actuarial loss (gain)	(6)	0	(17)	0
Net periodic benefit cost (return)	$ 3	$ 9	$ 11	$ 29