Stock-Based Compensation (Summary Of Compensation Costs) (Details) (USD $)	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation within operations and maintenance expense	$ 0	$ 0
Income tax benefit	104,000	73,000
Performance Share Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation within operations and maintenance expense	1,078,000	1,002,000
Income tax benefit	439,000	410,000
Restricted Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation within operations and maintenance expense	263,000	236,000
Income tax benefit	109,000	98,000
Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation within operations and maintenance expense	0	92,000
Income tax benefit		$ 38,000