Employee Stock And Incentive Plan (Summary Of Compensation Costs) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Income tax benefit	$ 167	$ 414	$ 595
Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation within opertions and maintenance expense	2,280	546	245
Income tax benefit	643	184	208
Performance Share Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation within opertions and maintenance expense	2,741	4,817	4,351
Income tax benefit	767	1,344	1,766
Restricted Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation within opertions and maintenance expense	1,650	1,605	1,183
Income tax benefit	466	456	489
Stock Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation within opertions and maintenance expense	698	600	563
Income tax benefit	$ 202	$ 173	$ 233