Postretirement Benefits (Details 2) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Defined Benefit Plan Disclosure [Line Items]
Service cost-benefits attributable to service during the period	$ 58	$ 53	$ 65
Interest cost on accumulated postretirement benefit obligation	117	128	130
Net amortization and deferral	19	30	47
Net periodic postretirement benefit cost	194	211	242
Net (gain) / loss during the year	166	(184)	(204)
Plan amendment for acquisition	0	12	0
Amortization of prior service cost and actuarial losses	(19)	(30)	(47)
Total recognized in comprehensive income	147	(202)	(251)
Total recognized in net periodic postretirement benefit cost and other comprehensive income	$ 341	$ 9	$ (9)