Employee Benefit Plans (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Pension Benefits
Components of the net periodic benefit cost
Interest cost	$ 32	$ 39	$ 65	$ 78
Recognized net actuarial loss	61	63	122	126
Benefit cost (income)	93	102	187	204
Postretirement Benefits
Components of the net periodic benefit cost
Interest cost	190	282	377	582
Service cost	75	106	162	229
Amortization of prior service cost	(228)	0	(456)	0
Benefit cost (income)	$ 37	$ 388	$ 83	$ 811