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Pay vs Performance Disclosure | 12 Months Ended
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Dec. 31, 2022 USD ($) $ / shares | Dec. 31, 2021 USD ($) $ / shares | Dec. 31, 2020 USD ($) $ / shares | Dec. 31, 2019 USD ($)
Pay vs Performance Disclosure [Table] |  |  |  |
Pay vs Performance [Table Text Block] | The Compensation Committee did not consider the pay versus performance disclosure below in making its pay decisions for any of the years shown.
|  |  |  |  |  |  |  |  | Value of initial Fixed $100 Investment Based on: |  |  |  | Company-Selected Performance Measure |  |
| Summary Compensation Table Total for Linden R. Evans (1) |  | Compensation Actually Paid to Linden R. Evans (1) (2) (3) |  | Average Summary Compensation Table Total for Non-PEO NEOs (1) |  | Average Compensation Actually Paid to Non-PEO NEOs (1) (2) (3) |  | Total Shareholder Return |  | Peer Group Total Shareholder Return (4) |  | Net income (GAAP), in millions |  | EPS from ongoing operations, as adjusted (non-GAAP) |  | (5)
2022 | $ | 4,486,548 |  | $ | 4,506,289 |  | $ | 1,208,492 |  | $ | 1,224,584 |  | $ | 99.15 |  | $ | 101.15 |  | $ | 270.8 |  | $ | 3.97 |  |
2021 | $ | 4,440,908 |  | $ | 5,151,457 |  | $ | 1,318,764 |  | $ | 1,453,664 |  | $ | 96.19 |  | $ | 117.12 |  | $ | 251.3 |  | $ | 3.74 |  |
2020 | $ | 4,221,114 |  | $ | 3,055,790 |  | $ | 1,565,573 |  | $ | 1,003,991 |  | $ | 80.92 |  | $ | 98.84 |  | $ | 242.8 |  | $ | 3.73 |  |
Named Executive Officers, Footnote [Text Block] | The individuals comprising the Non-PEO NEOs for each year presented are listed below:
2020 | 2021 | 2022
Richard W. Kinzley | Richard W. Kinzley | Richard W. Kinzley
Brian G. Iverson | Brian G. Iverson | Brian G. Iverson
Stuart A. Wevik | Stuart A. Wevik | Erik D. Keller
Scott A. Buchholz | Erik D. Keller | Jennifer C. Landis
Peer Group Issuers, Footnote [Text Block] | (4) The Peer Group TSR set forth in this table utilizes the Edison Electric Institute Index (“EEI Index”), which we also utilize in the stock performance graph required by Item 201(e) of Regulation S-K included in our Annual Report for the year ended December 31, 2022. The comparison assumes $100 was invested for the period starting December 31, 2019, through the end of the listed year in the Company and in the EEI Index, respectively. All dollar values assume reinvestment of the pre-tax value of dividends paid by companies, where applicable, included in the EEI Index. Historical stock performance is not necessarily indicative of future stock performance. |  |  |
PEO Total Compensation Amount | $ 4,486,548 | $ 4,440,908 | $ 4,221,114 |
PEO Actually Paid Compensation Amount | 4,506,289 | 5,151,457 | 3,055,790 |
Non-PEO NEO Average Total Compensation Amount | 1,208,492 | 1,318,764 | 1,565,573 |
Non-PEO NEO Average Compensation Actually Paid Amount | $ 1,224,584 | 1,453,664 | 1,003,991 |
Adjustment to Non-PEO NEO Compensation Footnote [Text Block] | (5) We determined EPS from ongoing operations, as adjusted (non-GAAP) to be the most important financial performance measure used to link Company performance to Compensation Actually Paid to our PEO and Non-PEO NEOs in 2022. This performance measure may not have been the most important financial performance measure for years 2021 and 2020 and we may determine a different financial performance measure to be the most important financial performance measure in future years. |  |  |
Equity Valuation Assumption Difference, Footnote [Text Block] | The amounts in the Inclusion of Equity Values in the tables above are derived from the amounts set forth in the following tables:
Year |  | Year-End Fair Value of Equity Awards Granted During Year That Remained Unvested as of Last Day of Year for Linden R. Evans |  |  | Change in Fair Value from Last Day of Prior Year to Last Day of Year of Unvested Equity Awards for Linden R. Evans |  |  | Vesting-Date Fair Value of Equity Awards Granted During Year that Vested During Year for Linden R. Evans |  |  | Change in Fair Value from Last Day of Prior Year to Vesting Date of Unvested Equity Awards that Vested During Year for Linden R. Evans |  |  | Fair Value at Last Day of Prior Year of Equity Awards Forfeited During Year for Linden R. Evans |  |  | Value of Dividends or Other Earnings Paid on Stock or Option Awards Not Otherwise Included for Linden R. Evans |  |  | Total - Inclusion of Equity Values for Linden R. Evans |
2022 |  | $ | 2,543,388 |  |  | $ | 157,935 |  |  | $ | - |  |  | $ | (286,806 | ) |  | $ | - |  |  | $ | - |  |  | $ | 2,414,517 |
2021 |  | $ | 2,919,069 |  |  | $ | 80,463 |  |  | $ | - |  |  | $ | (50,454 | ) |  | $ | - |  |  | $ | - |  |  | $ | 2,949,078 |
2020 |  | $ | 1,183,535 |  |  | $ | (259,008 | ) |  | $ | - |  |  | $ | (190,152 | ) |  | $ | - |  |  | $ | - |  |  | $ | 734,375 |
Year |  | Average Year-End Fair Value of Equity Awards Granted During Year That Remained Unvested as of Last Day of Year for Non-PEO NEOs |  |  | Average Change in Fair Value from Last Day of Prior Year to Last Day of Year of Unvested Equity Awards for Non-PEO NEOs |  |  | Average Vesting-Date Fair Value of Equity Awards Granted During Year that Vested During Year for Non-PEO NEOs |  |  | Average Change in Fair Value from Last Day of Prior Year to Vesting Date of Unvested Equity Awards that Vested During Year for Non-PEO NEOs |  |  | Average Fair Value at Last Day of Prior Year of Equity Awards Forfeited During Year for Non-PEO NEOs |  |  | Average Value of Dividends or Other Earnings Paid on Stock or Option Awards Not Otherwise Included for Non-PEO NEOs |  |  | Total - Average Inclusion of Equity Values for Non-PEO NEOs |
2022 |  | $ | 511,412 |  |  | $ | 30,488 |  |  | $ | - |  |  | $ | (44,278 | ) |  | $ | - |  |  | $ | - |  |  | $ | 497,622 |
2021 |  | $ | 624,512 |  |  | $ | 23,290 |  |  | $ | - |  |  | $ | (5,655 | ) |  | $ | - |  |  | $ | - |  |  | $ | 642,147 |
2020 |  | $ | 263,362 |  |  | $ | (68,513 | ) |  | $ | - |  |  | $ | (80,427 | ) |  | $ | - |  |  | $ | - |  |  | $ | 114,422 |
Compensation Actually Paid vs. Total Shareholder Return [Text Block] | (3) Compensation Actually Paid reflects the exclusions and inclusions of certain amounts for the PEO and the Non-PEO NEOs as set forth below. Equity values are calculated in accordance with FASB ASC Topic 718. Amounts in the Exclusion of Stock Awards column are the totals from the Stock Awards column set forth in the Summary Compensation Table. Amounts in the Exclusion of Change in Pension Value column reflect the amounts attributable to the Change in Pension Value reported in the Summary Compensation Table. Amounts in the Inclusion of Pension Service Cost are based on the service cost for services rendered during the listed year.
Year |  | Summary Compensation Table Total for Linden R. Evans |  |  | Exclusion of Change in Pension Value for Linden R. Evans |  |  | Exclusion of Stock Awards for Linden R. Evans |  |  | Inclusion of Pension Service Cost for Linden R. Evans |  |  | Inclusion of Equity Values for Linden R. Evans |  |  | Compensation Actually Paid to Linden R. Evans |
2022 |  | $ | 4,486,548 |  |  | $ | - |  |  | $ | (2,394,776 | ) |  | $ | - |  |  | $ | 2,414,517 |  |  | $ | 4,506,289 |
2021 |  | $ | 4,440,908 |  |  | $ | - |  |  | $ | (2,238,529 | ) |  | $ | - |  |  | $ | 2,949,078 |  |  | $ | 5,151,457 |
2020 |  | $ | 4,221,114 |  |  | $ | (79,100 | ) |  | $ | (1,820,599 | ) |  | $ | - |  |  | $ | 734,375 |  |  | $ | 3,055,790 |
Year |  | Average Summary Compensation Table Total for Non-PEO NEOs |  |  | Average Exclusion of Change in Pension Value for Non-PEO NEOs |  |  | Average Exclusion of Stock Awards and Option Awards for Non-PEO NEOs |  |  | Average Inclusion of Pension Service Cost for Non-PEO NEOs |  |  | Average Inclusion of Equity Values for Non-PEO NEOs |  |  | Average Compensation Actually Paid to Non-PEO NEOs |
2022 |  | $ | 1,208,492 |  |  | $ | - |  |  | $ | (481,530 | ) |  | $ | - |  |  | $ | 497,622 |  |  | $ | 1,224,584 |
2021 |  | $ | 1,318,764 |  |  | $ | (37,453 | ) |  | $ | (478,922 | ) |  | $ | 9,128 |  |  | $ | 642,147 |  |  | $ | 1,453,664 |
2020 |  | $ | 1,565,573 |  |  | $ | (304,177 | ) |  | $ | (405,174 | ) |  | $ | 33,347 |  |  | $ | 114,422 |  |  | $ | 1,003,991 |
Total Shareholder Return Vs Peer Group [Text Block] | As presented, the first chart below compares the Company's TSR and peer group TSR, assumes an initial investment of $100 on December 31, 2019, assumes all dividends were reinvested and depicts performance at the end of each applicable year. |  |  |
Tabular List [Table Text Block] | Financial Performance Measures The following table presents the financial performance measures that the Company considers to have been the most important in linking Compensation Actually Paid to our PEO and other NEOs for 2022 to Company performance. The measures in this table are not ranked.
Most Important Performance Measures
EPS from ongoing operations, as adjusted (non-GAAP)
Net income
Total Shareholder Return
Total Shareholder Return Amount | $ 99.15 | 96.19 | 80.92 |
Peer Group Total Shareholder Return Amount | 101.15 | 117.12 | 98.84 |
Net Income (Loss) | $ 270,800,000 | $ 251,300,000 | $ 242,800,000 |
Company Selected Measure Amount | 397 | 374 | 373 |
Adjustment to Compensation Amount |  |  |  | $ 100
Additional 402(v) Disclosure [Text Block] | (2) The amounts shown for Compensation Actually Paid have been calculated in accordance with Item 402(v) of Regulation S-K and do not reflect compensation actually earned, realized, or received by the Company's NEOs. These amounts reflect the Summary Compensation Table Total with certain adjustments as described in footnote (3) below. |  |  |
Earnings per share available for common stock | $ / shares | $ 3.97 | $ 3.74 | $ 3.65 |
Impairment of investment | $ / shares |  |  | 0.08 |
Earnings per share from ongoing operations, as adjusted | $ / shares | $ 3.97 | $ 3.74 | $ 3.73 |
Measure [Axis]: 1 |  |  |  |
Pay vs Performance Disclosure [Table] |  |  |  |
Measure Name | EPS from ongoing operations, as adjusted (non-GAAP) |  |  |
Non-GAAP Measure Description [Text Block] | A non-GAAP reconciliation to GAAP EPS is shown below:
EPS from ongoing operations, as adjusted (Non-GAAP Measure) |  |  |  |  |  |
| Year Ended December 31, |
| 2022 |  | 2021 |  | 2020 |
EPS available for common stock (GAAP) | $ | 3.97 |  | $ | 3.74 |  | $ | 3.65 |
Impairment of investment |  | — |  |  | — |  |  | 0.08 |
EPS from ongoing operations, as adjusted (Non-GAAP) | $ | 3.97 |  | $ | 3.74 |  | $ | 3.73 |
Measure [Axis]: 2 |  |  |  |
Pay vs Performance Disclosure [Table] |  |  |  |
Measure Name | Net income |  |  |
Measure [Axis]: 3 |  |  |  |
Pay vs Performance Disclosure [Table] |  |  |  |
Measure Name | Total Shareholder Return |  |  |
PEO [Member] |  |  |  |
Pay vs Performance Disclosure [Table] |  |  |  |
PEO Name | Linden R. Evans |  |  |
Peo Exclusion of Change in Pension Value | $ 0 | $ 0 | $ (79,100) |
Peo Exclusion of Stock Awards | (2,394,776) | (2,238,529) | (1,820,599) |
Peo Inclusion of Pension Service Cost | 0 | 0 | 0 |
Peo Inclusion of Equity Values | 2,414,517 | 2,949,078 | 734,375 |
Peo Year-End Fair Value of Equity Awards Granted During Year That Remained Unvested | 2,543,388 | 2,919,069 | 1,183,535 |
Peo Change in Fair Value from Last Day of Prior Year to Last Day of Year of Unvested Equity Awards | 157,935 | 80,463 | (259,008) |
Peo Vesting-Date Fair Value of Equity Awards Granted During Year that Vested During Year | 0 | 0 | 0 |
Peo Change in Fair Value from Last Day of Prior Year to Vesting Date of Unvested Equity Awards that Vested During Year | (286,806) | (50,454) | (190,152) |
Peo Fair Value at Last Day of Prior Year of Equity Awards Forfeited During Year | 0 | 0 | 0 |
Peo Value of Dividends or Other Earnings Paid on Stock or Option Awards Not Otherwise Included | 0 | 0 | 0 |
Peo Total - Inclusion of Equity Values | 2,414,517 | 2,949,078 | 734,375 |
Non-PEO NEO [Member] |  |  |  |
Pay vs Performance Disclosure [Table] |  |  |  |
Non Peo Neo Average Exclusion of Change in Pension Value | 0 | (37,453) | (304,177) |
Non Peo Neo Average Exclusion of Stock Awards and Option Awards | (481,530) | (478,922) | (405,174) |
Non Peo Neo Average Inclusion of Pension Service Cost | 0 | 9,128 | 33,347 |
Non Peo Neo Average Inclusion of Equity Values | 497,622 | 642,147 | 114,422 |
Non Peo Neo Average Year-End Fair Value of Equity Awards Granted During Year That Remained Unvested | 511,412 | 624,512 | 263,362 |
Non Peo Neo Average Change in Fair Value from Last Day of Prior Year to Last Day of Year of Unvested Equity Awards | 30,488 | 23,290 | (68,513) |
Non Peo Neo Average Vesting-Date Fair Value of Equity Awards Granted During Year that Vested During Year | 0 | 0 | 0 |
Non Peo Neo Average Change in Fair Value from Last Day of Prior Year to Vesting Date of Unvested Equity Awards that Vested During Year | (44,278) | (5,655) | (80,427) |
Non Peo Neo Average Fair Value at Last Day of Prior Year of Equity Awards Forfeited During Year | 0 | 0 | 0 |
Non Peo Neo Average Value of Dividends or Other Earnings Paid on Stock or Option Awards Not Otherwise Included | 0 | 0 | 0 |
Non Peo Neo Total - Average Inclusion of Equity Values | $ 497,622 | $ 642,147 | $ 114,422 |
Non-PEO NEO [Member] | Richard W. Kinzley |  |  |  |
Pay vs Performance Disclosure [Table] |  |  |  |
PEO Name | Richard W. Kinzley | Richard W. Kinzley | Richard W. Kinzley |
Non-PEO NEO [Member] | Brian G. Iverson |  |  |  |
Pay vs Performance Disclosure [Table] |  |  |  |
PEO Name | Brian G. Iverson | Brian G. Iverson | Brian G. Iverson |
Non-PEO NEO [Member] | Stuart A. Wevik |  |  |  |
Pay vs Performance Disclosure [Table] |  |  |  |
PEO Name |  | Stuart A. Wevik | Stuart A. Wevik |
Non-PEO NEO [Member] | Erik D. Keller |  |  |  |
Pay vs Performance Disclosure [Table] |  |  |  |
PEO Name | Erik D. Keller | Erik D. Keller |  |
Non-PEO NEO [Member] | Scott A. Buchholz |  |  |  |
Pay vs Performance Disclosure [Table] |  |  |  |
PEO Name |  |  | Scott A. Buchholz |
Non-PEO NEO [Member] | Jennifer C. Landis |  |  |  |
Pay vs Performance Disclosure [Table] |  |  |  |
PEO Name | Jennifer C. Landis |  |  |

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