| **Regulatory Assets And Liabilities (Components Of Regulatory Assets And Regulatory Liabilities) (Details) - USD ($) $ in Thousands** | Dec. 31, 2018 | Dec. 31, 2017 |
|---------------------------------------------------------------------------------------------------------------------------------------|---------------|---------------|
| **Regulatory Of Assets And Liabilities [Line Items]**                                                                                 |          |          |
| Regulatory Assets                                                                                                                     | $ 788,076     | $ 713,971     |
| Regulatory Liabilities                                                                                                                | 531,027       | 541,910       |
| Income Taxes [Member]                                                                                                                 |          |          |
| **Regulatory Of Assets And Liabilities [Line Items]**                                                                                 |          |          |
| Regulatory Assets                                                                                                                     | 657,378       | 584,067       |
| Regulatory Liabilities                                                                                                                | 414,787       | 438,750       |
| Customer Refunds Resulting From TCJA [Member]                                                                                         |          |          |
| **Regulatory Of Assets And Liabilities [Line Items]**                                                                                 |          |          |
| Regulatory Liabilities                                                                                                                | 4,593         |          |
| Utility Plant Retirement Costs [Member]                                                                                               |          |          |
| **Regulatory Of Assets And Liabilities [Line Items]**                                                                                 |          |          |
| Regulatory Assets                                                                                                                     | 6,743         | 5,367         |
| Regulatory Liabilities                                                                                                                | 38,435        | 35,249        |
| Postretirement Benefits [Member]                                                                                                      |          |          |
| **Regulatory Of Assets And Liabilities [Line Items]**                                                                                 |          |          |
| Regulatory Assets                                                                                                                     | 110,719       | 112,532       |
| Regulatory Liabilities                                                                                                                | 71,285        | 65,964        |
| Accrued Vacation [Member]                                                                                                             |          |          |
| **Regulatory Of Assets And Liabilities [Line Items]**                                                                                 |          |          |
| Regulatory Assets                                                                                                                     | 2,447         | 2,198         |
| Water Tank Painting [Member]                                                                                                          |          |          |
| **Regulatory Of Assets And Liabilities [Line Items]**                                                                                 |          |          |
| Regulatory Assets                                                                                                                     | 2,864         | 3,259         |
| Regulatory Liabilities                                                                                                                | 1,855         | 1,855         |
| Fair Value Adjustment Of Long-Term Debt Assumed In Acquisition [Member]                                                               |          |          |
| **Regulatory Of Assets And Liabilities [Line Items]**                                                                                 |          |          |
| Regulatory Assets                                                                                                                     | 2,533         | 2,901         |
| Rate Case Filing Expenses And Other [Member]                                                                                          |          |          |
| **Regulatory Of Assets And Liabilities [Line Items]**                                                                                 |          |          |
| Regulatory Assets                                                                                                                     | 5,392         | 3,647         |
| Regulatory Liabilities                                                                                                                | $ 72          | $ 92          |

| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
The amount for the individual regulatory asset as itemized in a table of regulatory assets as of the end of the period.
+ References
Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 980 -SubTopic 340 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6499975&loc=d3e44250-110382
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| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
The amount for the individual regulatory liability as itemized in a table of regulatory liabilities as of the end of the period.
+ References
Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 980 -SubTopic 405 -Section 25 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6500807&loc=d3e48068-110394
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| X                                                                                                                                                                                                                                                                          |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Regulatory Of Assets And Liabilities [Line Items]
+ 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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| X                                                                                                                                               |
|-------------------------------------------------------------------------------------------------------------------------------------------------|
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| X                                                                                                                                                                                   |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
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| X                                                                                                                                                            |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------|
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