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, 2019	Mar. 31, 2018
Pension Benefits
Plan expense for noncontributory benefit pension plan and post-retirement health and life plans
Service cost	$ 0	$ 0
Interest cost	273	266
Expected return on plan assets	(363)	(518)
Recognized actuarial loss (gain)	86	87
Net periodic benefit (return) cost	(4)	(165)
Other Benefits
Plan expense for noncontributory benefit pension plan and post-retirement health and life plans
Service cost	2	2
Interest cost	8	9
Expected return on plan assets	0	0
Recognized actuarial loss (gain)	(14)	0
Net periodic benefit (return) cost	$ (4)	$ 11