Stock-Based Compensation (Summary Of Compensation Costs) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation within operations and maintenance expenses	$ 279	$ 637	$ 1,046	$ 1,625
Income tax benefit	79	180	296	458
Performance Share Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation within operations and maintenance expenses	918	584	2,364	2,434
Income tax benefit	252	166	660	682
Restricted Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation within operations and maintenance expenses	550	395	1,582	1,231
Income tax benefit	148	112	438	348
Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation within operations and maintenance expenses	103		220
Income tax benefit	30		64
Stock Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation within operations and maintenance expenses	175	158	520	540
Income tax benefit	$ 50	$ 46	$ 150	$ 156