Employee Benefit Plan - Components of Net Periodic Benefit Cost (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Pension Plan
Components of net periodic benefit cost
Service cost	$ 0	$ 0
Interest cost	745	591
Expected return on plan assets	(1,234)	(1,417)
Amortization of net retirement plan actuarial loss	337	267
Amortization of net retirement plan prior service (credit) cost	(3)	(3)
Net periodic benefit (income) cost	(155)	(562)
Life and Health
Components of net periodic benefit cost
Service cost	50	53
Interest cost	73	65
Expected return on plan assets	0	0
Amortization of net retirement plan actuarial loss	0	15
Amortization of net retirement plan prior service (credit) cost	(15)	(15)
Net periodic benefit (income) cost	108	118
SERP Benefits
Components of net periodic benefit cost
Service cost	37	45
Interest cost	229	206
Expected return on plan assets	0	0
Amortization of net retirement plan actuarial loss	85	135
Amortization of net retirement plan prior service (credit) cost	22	22
Net periodic benefit (income) cost	$ 373	$ 408