Retirement Plan (Effect of One Percent Change in Health Care Cost Trend Rates) (Details) - Defined Benefit Post-retirement Health Coverage [Member] $ in Thousands	12 Months Ended
	Dec. 31, 2016 USD ($)
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
One Percent Increase, Service Cost	$ 187
One Percentage Point Decrease on Service Cost	(156)
One Percent Increase, Interest Cost	56
One Percentage Point Decrease, Interest Cost	(49)
One Percentage Point Increase on Accumulated Post-retirement Benefit Obligation	1,286
One Percentage Point Decrease on Accumulated Post-retirement Benefit Obligation	$ (1,118)