Stock-Based Compensation (Summary Of Compensation Costs) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation for stock options within operations and maintenance expenses	$ 124	$ 329	$ 371	$ 769
Income tax benefit	162	46	295	420
Performance Share Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation for stock options within operations and maintenance expenses	610	260	1,058	361
Restricted Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation for stock options within operations and maintenance expenses	172	102	301	141
Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation for stock options within operations and maintenance expenses	$ 741	$ 711	$ 1,136	$ 1,100