Employee Benefit Plan (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Pension Plan
Components of net periodic benefit cost
Service cost	$ 0	$ 0
Interest cost	607	649
Expected return on plan assets	(1,267)	(1,215)
Amortization of net retirement plan actuarial loss	252	239
Amortization of net retirement plan prior service (credit) cost	(3)	(4)
Net periodic benefit (income) cost	(411)	(331)
Life and Health
Components of net periodic benefit cost
Service cost	68	82
Interest cost	71	77
Expected return on plan assets	0	0
Amortization of net retirement plan actuarial loss	4	1
Amortization of net retirement plan prior service (credit) cost	4	4
Net periodic benefit (income) cost	147	164
SERP Benefits
Components of net periodic benefit cost
Service cost	54	72
Interest cost	209	211
Expected return on plan assets	0	0
Amortization of net retirement plan actuarial loss	101	104
Amortization of net retirement plan prior service (credit) cost	22	30
Net periodic benefit (income) cost	$ 386	$ 417