Employee Benefit Plans (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Pension Benefits
Components of the net periodic benefit cost
Interest cost	$ 38	$ 49	$ 116	$ 145
Recognized net actuarial loss	63	36	189	109
Benefit cost (income)	101	85	305	254
Postretirement Benefits
Components of the net periodic benefit cost
Service cost	81	190	310	570
Interest cost	202	387	784	1,162
Amortization of prior service cost	(228)	(88)	(228)	(266)
Recognized net actuarial loss	0	192	0	576
Benefit cost (income)	$ 55	$ 681	$ 866	$ 2,042