Selected Quarterly Financial Data (Unaudited) (Schedule Of Quarterly Results Of Operations) (Details) - USD ($) $ in Thousands	3 Months Ended												12 Months Ended
	Dec. 31, 2016		Sep. 30, 2016		Jun. 30, 2016		Mar. 31, 2016		Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016		Dec. 31, 2015	Dec. 31, 2014
Quarterly Financial Information Disclosure [Abstract]
Operating Revenues	$ 199,461		$ 222,802		$ 199,149		$ 256,459		$ 224,166	$ 254,265	$ 249,341	$ 292,256	$ 877,871		$ 1,020,028	$ 951,576
Operating Margin	14,062		9,022		9,884		12,224		6,249	13,297	14,214	15,193	45,192		48,953	50,525
Net Margin attributable to ODEC	$ 8,738	[1]	$ 2,991	[1]	$ 2,955	[1]	$ 2,953	[1]	$ 2,988	$ 3,005	$ 2,992	$ 2,894	$ 17,637	[1]	$ 11,879	$ 9,100

[1] For the fourth quarter of 2016, includes an equity contribution of $5.8 million.