Employee Benefit Plans (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Pension Benefits
Components of the net periodic benefit cost
Service cost	$ 0	$ 0	$ 0	$ 0
Interest cost	39	48	78	97
Recognized net actuarial loss	63	37	126	73
Benefit cost (income)	102	85	204	170
Postretirement Benefits
Components of the net periodic benefit cost
Service cost	106	167	229	380
Interest cost	282	370	582	775
Amortization of prior service cost	0	(89)	0	(177)
Recognized net actuarial loss	0	149	0	384
Benefit cost (income)	$ 388	$ 597	$ 811	$ 1,362