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, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 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	315	256	588	522
Expected return on plan assets	(362)	(520)	(725)	(1,038)
Recognized actuarial loss (gain)	135	77	221	164
Net periodic benefit (return) cost	88	(187)	84	(352)
Other Benefits
Plan expense for noncontributory benefit pension plan and post-retirement health and life plans
Service cost	1	2	3	4
Interest cost	8	7	16	16
Expected return on plan assets	0	0	0	0
Recognized actuarial loss (gain)	3	0	(11)	0
Net periodic benefit (return) cost	$ 12	$ 9	$ 8	$ 20