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Share-based Compensation Plans (Tables) | 12 Months Ended
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Dec. 31, 2023
Share-Based Payment Arrangement [Abstract] |
Share-based Payment Arrangement, Expensed Amount | Stock-based compensation expense, which is included in Operations and maintenance on the accompanying Consolidated Statements of Income, was as follows for the ye ars ended December 31 (in millions):
| 2023 |  | 2022 |  | 2021 |
Stock-based compensation expense | $ | 7.0 |  | $ | 8.6 |  | $ | 9.7 |
Schedule of Share-based Compensation, Restricted Stock and Restricted Stock Units Activity | A summary of the status of the restricted stock and restricted stock units at December 31, 2023, was as follows:
| Restricted Stock |  | Weighted-Average Grant Date Fair Value |
Balance at January 1, 2023 |  | 178,129 |  | $ | 67.23 |
Granted |  | 110,198 |  |  | 63.33 |
Vested |  | (97,084 | ) |  | 67.56 |
Forfeited |  | (26,556 | ) |  | 65.10 |
Balance at December 31, 2023 |  | 164,687 |  | $ | 64.81 |
The weighted-average grant-date fair value of restricted stock granted, and the total fair value of shares vested during the years ended December 31, were as follows:
| Weighted-Average Grant Date Fair Value |  | Total Fair Value of Shares Vested |
|  |  | (in millions) |
2023 | $ | 63.33 |  | $ | 5.9 |
2022 | $ | 69.03 |  | $ | 6.4 |
2021 | $ | 65.64 |  | $ | 5.4 |
Disclosure of Share-based Compensation Arrangements by Share-based Payment Award | The outstanding performance periods at December 31, 2023 were as follows:
|  |  | Possible Payout Range of Target
Grant Date | Performance Period | Target Grant of Shares | Minimum | Maximum
January 1, 2020 | January 1, 2020 - December 31, 2022 | 35,571 | 0% | 200%
A summary of the status of the Performance Share Plan at December 31, 2023 was as follows:
| Equity Portion |  | Liability Portion |
|  |  | Weighted-Average Grant Date |  |  |  | Weighted-Average Fair Value at |
| Shares |  | Fair Value (a) |  | Shares |  | December 31, 2023 |
Performance Shares balance at beginning of period |  | 18,105 |  | $ | 81.42 |  |  | 18,105 |  |  |
Granted |  | — |  |  | — |  |  | — |  |  |
Forfeited |  | — |  |  | — |  |  | — |  |  |
Vested |  | (18,105 | ) |  | 81.42 |  |  | (18,105 | ) |  |
Performance Shares balance at end of period |  | — |  | $ | — |  |  | — |  | $ | — |
(a) The grant date fair values for the performance shares granted in 2020 were determined by Monte Carlo simulation using a blended volatility o f 18%, comprised of 50% historical volatility and 50% implied volatility and the average risk-free interest rate of the three-year United States Treasury security rate in effect as of the grant date.
Performance Plan Payouts | Performance plan payouts have been as follows (in millions, except stock issued):
Performance Period | Year Paid | Stock Issued |  | Cash Paid |  | Total Intrinsic Value |
January 1, 2020 to December 31, 2022 | 2023 |  | 4,958 |  | $ | 0.3 |  | $ | 0.7 |
January 1, 2019 to December 31, 2021 | 2022 |  | 7,582 |  | $ | 0.5 |  | $ | 1.0 |
January 1, 2018 to December 31, 2020 | 2021 |  | 27,515 |  | $ | 1.6 |  | $ | 3.3 |
Schedule of Share-based Payment Award, Stock Options, Valuation Assumptions | The Monte Carlo simulation is used to estimate expected share payout based on the Company’s TSR for a three-year performance period relative to the designated peer group beginning January 1 of the award year. The significant assumptions included in the company's Monte Carlo simulations were as follows:
| 2023 | 2022
Fair value of share units award | $77.95 | $74.48
Risk-free rate | 3.84% | 0.97%
Black Hills Corporation’s common stock volatility | 31% | 30%
Volatility range for the peer group | 24-39% | 22-67%
Schedule of Nonvested Share Activity | The following table summarizes the performance share unit activity for the year ended December 31, 2023:
| Performance Share Units - Market Condition |  | Performance Share Units - Performance Condition |
| Share Units |  | Weighted-Average Fair Value per Share Unit |  | Share Units |  | Weighted-Average Fair Value per Share Unit |
Nonvested at January 1, 2023 |  | 68,474 |  | $ | 69.91 |  |  | 45,666 |  | $ | 66.19 |
Granted |  | 50,440 |  |  | 77.95 |  |  | 21,615 |  |  | 71.50 |
Forfeited |  | (8,167 | ) |  | 73.43 |  |  | (4,627 | ) |  | 68.03 |
Nonvested at December 31, 2023 |  | 110,747 |  | $ | 73.31 |  |  | 62,654 |  | $ | 67.88 |

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