Income Taxes (Schedule of Net Deferred Tax Liability) (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Utility Plant Related	$ 69,019	$ 63,281
Customer Advances	(3,430)	(3,510)
Employee Benefits	6,904	5,796
Investment Tax Credits (ITC)	753	832
Net Operating Loss Carryforwards		2,311
Other	(421)	(176)
Total Deferred Tax Liability and ITC	$ 72,825	$ 68,534