Summary Of Significant Accounting Policies (Schedule Of Revenues From Sales To Non-Members) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Accounting Policies [Abstract]
Sales to non-members excluding renewable energy credit sales	$ 21,645	$ 42,556	$ 37,635
Renewable energy credit sales to non-members	9,132	8,547	5,908
Total Sales to Non-members	$ 30,777	$ 51,103	$ 43,543