| **Consolidated Statements Of Operations And Comprehensive Income - USD ($) shares in Thousands, $ in Thousands** | 3 Months Ended |
|------------------------------------------------------------------------------------------------------------------|----------------|
||
| **Consolidated Statements Of Net Income [Abstract]**                                                             |           |   |
| Operating revenues                                                                                               | $ 201,132      | $ 194,347 |
| **Operating expenses:**                                                                                          |           |   |
| Operations and maintenance                                                                                       | 79,314         | 73,946 |
| Depreciation                                                                                                     | 39,074         | 35,967 |
| Amortization                                                                                                     | 336            | 130 |
| Taxes other than income taxes                                                                                    | 14,969         | 14,967 |
| Total operating expenses                                                                                         | 133,693        | 125,010 |
| Operating income                                                                                                 | 67,439         | 69,337 |
| **Other expense (income):**                                                                                      |           |   |
| Interest expense, net                                                                                            | 27,850         | 23,471 |
| Allowance for funds used during construction                                                                     | (4,056)        | (2,867) |
| Change in fair value of interest rate swap agreements                                                            | 34,782         |   |
| Gain on sale of other assets                                                                                     | (220)          | (196) |
| Equity earnings in joint venture                                                                                 | (543)          | (382) |
| Other                                                                                                            | 872            | 603 |
| Provision for income tax benefit                                                                                 | 8,754          | 48,708 |
| Provision for income taxes                                                                                       | (8,170)        | (2,131) |
| Net income                                                                                                       | 16,924         | 50,839 |
| Comprehensive income                                                                                             | $ 16,924       | $ 50,839 |
| **Net income per common share:**                                                                                 |           |   |
| Basic                                                                                                            | $ 0.09         | $ 0.29 |
| Diluted                                                                                                          | $ 0.09         | $ 0.29 |
| **Average common shares outstanding during the period:**                                                         |           |   |
| Basic                                                                                                            | 178,213        | 177,801 |
| Diluted                                                                                                          | 178,552        | 178,238 |

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| - Definition
The aggregate amount of recurring noncash expense charged against earnings in the period to allocate the cost of assets over their estimated remaining economic lives.
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| - Definition
Amount after tax of increase (decrease) in equity from transactions and other events and circumstances from net income and other comprehensive income, attributable to parent entity. Excludes changes in equity resulting from investments by owners and distributions to owners.
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Total costs of sales and operating expenses for the period.
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The amount of expense recognized in the current period that reflects the allocation of the cost of tangible assets over the assets' useful lives. Includes production and non-production related depreciation.
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| - Definition
The amount of net income (loss) for the period per each share of common stock or unit outstanding during the reporting period.
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The amount of net income (loss) for the period available to each share of common stock or common unit outstanding during the reporting period and to each share or unit that would have been outstanding assuming the issuance of common shares or units for all dilutive potential common shares or units outstanding during the reporting period.
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Aggregate net gain (loss) on all derivative instruments recognized in earnings during the period, before tax effects.
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Amount of gain (loss) on sale or disposal of other assets.
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Amount of income (loss) from continuing operations before deduction of income tax expense (benefit) and income (loss) attributable to noncontrolling interest, and addition of income (loss) from equity method investments.
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Amount of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.
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| - Definition
Amount of the cost of borrowed funds accounted for as interest expense.
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The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.
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Amount after tax of income (loss) attributable to nonredeemable noncontrolling shareholder, unit holder, partner, or other equity holder of a joint venture.
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The net result for the period of deducting operating expenses from operating revenues.
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Amount of income (expense) related to nonoperating activities, classified as other.
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Total increase in earnings in the period representing the cost of equity (based on assumed rate of return) and/or borrowed funds (based on interest rate) used to finance construction of regulated assets, which is expected to be recovered through rate adjustments.
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Amount of revenue recognized from goods sold, services rendered, insurance premiums, or other activities that constitute an earning process. Includes, but is not limited to, investment and interest income before deduction of interest expense when recognized as a component of revenue, and sales and trading gain (loss).
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| - Definition
Amount of operating expense for routine plant maintenance, repairs and operations of regulated operation.
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| - Definition
Amount of operating expense for taxes other than income taxes of regulated operation.
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| - Definition
The average number of shares or units issued and outstanding that are used in calculating diluted EPS or earnings per unit (EPU), determined based on the timing of issuance of shares or units in the period.
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| - Definition
Number of [basic] shares or units, after adjustment for contingently issuable shares or units and other shares or units not deemed outstanding, determined by relating the portion of time within a reporting period that common shares or units have been outstanding to the total time in that period.
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