| **Regulatory Assets And Liabilities (Narrative) (Details) - USD ($)**    | 12 Months Ended |
|--------------------------------------------------------------------------|-----------------|
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| **Regulatory Assets And Liabilities [Line Items]**                       |            |   |   |
| Amortization of deferred repair tax adjustment                           | $ 38,000,000    |   |   |
| Amortization period                                                      | 10 years        |   |   |
| Increase in net income                                                   | $ 16,734,000    |   |   |
| Statutory federal tax rate                                               | 21.00%          | 35.00% | 35.00% |
| Regulatory assets                                                        | $ 788,076,000   | $ 713,971,000 |   |
| Regulatory liabilities                                                   | 531,027,000     | 541,910,000 |   |
| Change in Accounting Method Accounted for as Change in Estimate [Member] |            |   |   |
| **Regulatory Assets And Liabilities [Line Items]**                       |            |   |   |
| Regulatory assets                                                        | (357,262,000)   | (357,262,000) |   |
| Regulatory liabilities                                                   | 303,320,000     | 303,320,000 |   |
| Impact on cash flows                                                     | $ 0             | $ 0 |   |
| Scenario, Plan [Member]                                                  |            |   |   |
| **Regulatory Assets And Liabilities [Line Items]**                       |            |   |   |
| Statutory federal tax rate                                               | 21.00%          |   |   |
| Minimum [Member]                                                         |            |   |   |
| **Regulatory Assets And Liabilities [Line Items]**                       |            |   |   |
| Water tank painting costs amortization period                            | 1 year          |   |   |
| Maturity date                                                            | 2022            |   |   |
| Rate case filing expense amortization period                             | 1 year          |   |   |
| Maximum [Member]                                                         |            |   |   |
| **Regulatory Assets And Liabilities [Line Items]**                       |            |   |   |
| Water tank painting costs amortization period                            | 15 years        |   |   |
| Maturity date                                                            | 2029            |   |   |
| Rate case filing expense amortization period                             | 5 years         |   |   |
| Postretirement Benefits [Member]                                         |            |   |   |
| **Regulatory Assets And Liabilities [Line Items]**                       |            |   |   |
| Regulatory asset recovery period                                         | 10 years        |   |   |

| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                       |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Percentage of domestic federal statutory tax rate applicable to pretax income (loss).
+ References
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| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
The increase (decrease) during the reporting period in the value of assets that are created when regulatory agencies permits public utilities to defer costs (revenues) to the balance sheet. This element is a the increase (decrease) of regulatory assets and liabilities combined.
+ References
Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=109223946&loc=d3e3602-108585
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| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Carrying amount as of the balance sheet date of capitalized costs of regulated entities that are not expected to be recovered through revenue sources within one year or the normal operating cycle if longer.
+ References
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| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                 |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
The amount for the individual regulatory noncurrent liability as itemized in a table of regulatory noncurrent liabilities as of the end of the period.
+ References
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| X                                                                                                                                                                                                                                                                            |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amortizataion period of rate case filing expense
+ References
No definition available.
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| X                                                                                                                                                                                                                                                                            |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amortization of deferred repair tax adjustment
+ References
No definition available.
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| X                                                                                                                                                                                                                                                                                                                            |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amortization Of Deferred Repair Tax Adjustment Impact On Net Income Loss
+ References
No definition available.
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| X                                                                                                                                                                                                                                                 |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Debt Instrument, Maturity Date, Year
+ References
No definition available.
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| X                                                                                                                                                                                                                                               |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Regulatory Asset Recovery Period
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No definition available.
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| X                                                                                                                                                                                                                                                                     |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Regulatory Assets And Liabilities [Line Items]
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No definition available.
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| X                                                                                                                                                                                                                                                    |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Tax Adjustment, Amortization Period
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No definition available.
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| X                                                                                                                                                                                                                                                                             |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Water tank painting costs amortized over a period.
+ References
No definition available.
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| X                                                                                                                                                                                                         |
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| X                                                                                                                                                |
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| X                                                                                                                       |
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| X                                                                                                                       |
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| X                                                                                                                                                            |
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