| **Stock-Based Compensation (Summary Of Compensation Costs) (Details) - USD ($)**   | 3 Months Ended | 9 Months Ended |
|------------------------------------------------------------------------------------|----------------|----------------|
||
| 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                                                                 | $ 15,000       | $ 28,000       | 249,000 | 143,000 |
| Performance Share Units [Member]                                                   |           |           |   |   |
| **Share-based Compensation Arrangement by Share-based Payment Award [Line Items]** |           |           |   |   |
| Stock-based compensation within operations and maintenance expense                 | 1,012,000      | 836,000        | 2,504,000 | 3,475,000 |
| Income tax benefit                                                                 | 411,000        | 339,000        | 1,013,000 | 1,414,000 |
| Restricted Stock Units [Member]                                                    |           |           |   |   |
| **Share-based Compensation Arrangement by Share-based Payment Award [Line Items]** |           |           |   |   |
| Stock-based compensation within operations and maintenance expense                 | 299,000        | 209,000        | 763,000 | 888,000 |
| Income tax benefit                                                                 | 124,000        | $ 86,000       | 315,000 | 367,000 |
| Stock Compensation Plan [Member]                                                   |           |           |   |   |
| **Share-based Compensation Arrangement by Share-based Payment Award [Line Items]** |           |           |   |   |
| Stock-based compensation within operations and maintenance expense                 | 131,000        |           | 375,000 | 365,000 |
| Income tax benefit                                                                 | $ 54,000       |           | $ 155,000 | $ 151,000 |

| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Represents the expense recognized during the period arising from equity-based compensation arrangements (for example, shares of stock, unit, stock options or other equity instruments) with employees, directors and certain consultants qualifying for treatment as employees.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SAB Topic 14.F) -URI http://asc.fasb.org/extlink&oid=27013229&loc=d3e301413-122809Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5047-113901Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (h)(1)(i) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901
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| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
The total recognized tax benefit related to compensation cost for equity-based payment arrangements recognized in income during the period.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (h)(1)(i) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901
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| X                                                                                                                                                                                                                                                                                                                                                                                                                                                          |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.
+ References
No definition available.
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| X                                                                                                                                             |
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| X                                                                                                                                                   |
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| X                                                                                                                                                 |
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