Other Postretirement Benefits (Components of Net Periodic Postretirement Benefit Cost) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Interest cost	$ 59	$ 66	$ 88
Amortization of unrecognized prior service cost	6	14	15
Loss amortization (2)	(13)	0	0
Net periodic pension cost	$ 52	$ 80	$ 103
Discount rate	3.81%	3.94%	3.74%
Ultimate healthcare trend rates	4.00%
Other Postretirement Benefits
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	$ 22	$ 26	$ 16
Interest cost	272	300	255
Amortization of unrecognized prior service cost	44	44	44
Loss amortization (2)	134	197	78
Net periodic pension cost	$ 472	$ 567	$ 393
Discount rate	3.80%	3.90%	3.70%
Annual rate of increase in the per capita cost of: Medical costs before age 65	7.50%	7.80%	8.00%
Annual rate of increase in the per capita cost of: Medical costs after age 65	6.50%	6.80%	7.00%
Annual rate of increase in the per capita cost of: Prescription drug costs	10.50%	11.00%	9.00%