Retirement Plans - Change in Benefit Obligations and Plan Assets (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Pension plan
Change in benefit obligation - Pension
Benefit obligation at beginning of year	$ 9,905	$ 8,970
Service cost	15	223	$ 265
Interest cost	386	406	466
Actuarial gain/assumption changes	1,505	378
Benefits paid	(124)	(50)
Settlements paid	(1,588)	(22)
Benefit obligation at end of year	10,099	9,905	8,970
Accumulated benefit obligation at end of year	10,099	8,475
Change in Plan Assets
Fair value of plan assets at beginning of year	6,974	6,707
Actual return on plan assets	804	339
Employer contribution	165	0
Benefits/expenses paid	(124)	(50)
Settlements paid	0	(22)
Fair value of plan assets at end of year	7,819	6,974	6,707
Funded status - liability	(2,280)	(2,931)
Amounts recorded in stockholders’ equity
Net actuarial loss	2,973	3,465
Prior service cost	0	(61)
Total amount recorded	2,973	3,404
Amount recorded, net taxes	1,784	2,042
SERP
Change in benefit obligation - Pension
Benefit obligation at beginning of year	8,015	7,999
Service cost	0	0	0
Interest cost	287	323	278
Actuarial gain/assumption changes	466	129
Benefits paid	(444)	(436)
Curtailments	(565)	0
Benefit obligation at end of year	7,759	8,015	$ 7,999
Accumulated benefit obligation at end of year	7,759	7,482
Change in Plan Assets
Funded status - liability	(7,759)	(8,015)
Amounts recorded in stockholders’ equity
Net actuarial loss	1,935	2,248
Prior service cost	0	0
Total amount recorded	1,935	2,248
Amount recorded, net taxes	$ 1,161	$ 1,349