| **Consolidation and Nature of Operations (Details) - USD ($) $ in Thousands** | 9 Months Ended |          |
|-------------------------------------------------------------------------------|----------------|----------|
||
| **Cash paid during the period for:**                                          |           |     |   |
| Income taxes, net of refunds                                                  | $ 10,091       | $ 2,185  |   |
| Interest, net of amounts capitalized                                          | 161,875        | 147,149  |   |
| **Significant non-cash investing and financing activities:**                  |           |     |   |
| Accrued capital expenditures                                                  | 99,405         | 93,031   |   |
| Sale of 4CA's 7% interest in Four Corners                                     | 68,907         | 0        |   |
| APS                                                                           |           |     |   |
| **Cash paid during the period for:**                                          |           |     |   |
| Income taxes, net of refunds                                                  | 24,746         | 132      |   |
| Interest, net of amounts capitalized                                          | 154,788        | 142,779  |   |
| **Significant non-cash investing and financing activities:**                  |           |     |   |
| Accrued capital expenditures                                                  | $ 99,405       | $ 94,769 |   |
| APS | Four Corners                                                            |           |     |   |
| **Investment [Line Items]**                                                   |           |     |   |
| Ownership percentage                                                          | 7.00%          |     | 7.00% |

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| - Definition
Future cash outflow to pay for purchases of fixed assets that have occurred.
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| - Definition
The amount of cash paid during the current period to foreign, federal, state, and local authorities as taxes on income, net of any cash received during the current period as refunds for the overpayment of taxes.
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| - Definition
Amount of cash paid for interest, excluding capitalized interest, classified as operating activity. Includes, but is not limited to, payment to settle zero-coupon bond for accreted interest of debt discount and debt instrument with insignificant coupon interest rate in relation to effective interest rate of borrowing attributable to accreted interest of debt discount.
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The proportionate share of interest (percent) in a jointly owned utility plant.
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Amount of noncash consideration received for selling an asset or business through a noncash (or part noncash) transaction.
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