Employee Benefit Plans (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Pension Benefits
Components of the net periodic benefit cost
Service cost	$ 0	$ 0
Interest cost	39	48
Recognized net actuarial loss	63	36
Benefit cost (income)	102	84
Postretirement Benefits
Components of the net periodic benefit cost
Service cost	123	213
Interest cost	300	405
Amortization of prior service cost	0	(89)
Recognized net actuarial loss	0	235
Benefit cost (income)	$ 423	$ 764