Employee Benefit Plan (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Pension Plan
Components of net periodic benefit cost
Service cost	$ 0	$ 0	$ 0	$ 0
Interest cost	643	587	1,250	1,237
Expected return on plan assets	(1,256)	(1,207)	(2,523)	(2,422)
Amortization of net retirement plan actuarial loss	286	249	537	487
Amortization of net retirement plan prior service (credit) cost	(3)	(4)	(5)	(7)
Net periodic benefit (income) cost	(330)	(375)	(741)	(705)
Life and Health Three Months Ended
Components of net periodic benefit cost
Service cost	28	47	96	129
Interest cost	62	65	134	141
Expected return on plan assets	0	0	0	0
Amortization of net retirement plan actuarial loss	13	2	17	3
Amortization of net retirement plan prior service (credit) cost	(35)	4	(31)	8
Net periodic benefit (income) cost	68	118	216	281
SERP Benefits
Components of net periodic benefit cost
Service cost	29	14	83	86
Interest cost	217	205	426	416
Expected return on plan assets	0	0	0	0
Amortization of net retirement plan actuarial loss	98	75	199	179
Amortization of net retirement plan prior service (credit) cost	22	8	44	38
Net periodic benefit (income) cost	$ 366	$ 302	$ 752	$ 719