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Stock-Based Compensation - Narrative (Details) - USD ($) $ in Millions |  |  |  |  | 12 Months Ended |  |  |
--- | --- | --- | --- | --- | --- | --- | --- | ---
Sep. 16, 2024 | May 03, 2024 | Apr. 08, 2024 | Dec. 04, 2023 | Dec. 31, 2024 | Dec. 31, 2023 | Dec. 31, 2022 | Dec. 04, 2024 | May 31, 2023 | May 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |
Compensation expense for stock-based arrangements |  |  |  |  | $ 9.5 | $ 7.2 | $ 7.9 |  |  |
Conversion of equity based awards to common stock |  |  |  |  |  |  |  | 1 |  |
Restricted Shares and Performance-Based Shares |  |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |
Unrecognized compensation expense |  |  |  |  | $ 5.0 |  |  |  |  |
Period to recognize compensation expense |  |  |  |  | 2 years 3 months 3 days |  |  |  |  |
Restricted Stock |  |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |
Nonvested (in shares) |  |  |  |  | 241,237 | 212,080 |  |  |  |
Granted (in shares) |  |  |  |  | 249,282 |  |  |  |  |
Vested (in shares) |  |  |  |  | 218,403 |  |  |  |  |
PNM |  |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |
Compensation expense for stock-based arrangements |  |  |  |  | $ 5.0 | $ 4.8 | 5.3 |  |  |
TNMP |  |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |
Compensation expense for stock-based arrangements |  |  |  |  | $ 2.7 | $ 2.4 | $ 2.6 |  |  |
Executive | Performance Shares |  |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |
Shares excluded in year two (in shares) |  |  |  |  | 150,976 |  |  |  |  |
Shares excluded in year three (in shares) |  |  |  |  | 227,472 |  |  |  |  |
Performance period |  |  |  |  | 3 years |  |  |  |  |
Executive | Performance Shares | Achieved Performance Target for 2021 Through 2023 |  |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |
Shares excluded (in shares) |  |  |  |  | 80,492 |  |  |  |  |
Executive | Performance Shares | Achieved Performance Target for 2022 Through 2024 |  |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |
Shares excluded (in shares) |  |  |  |  | 49,489 |  |  |  |  |
Executive | Restricted Stock |  |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |
Number of shares vested at one-time sign-on (in shares) |  |  |  |  | 8,791 |  |  |  |  |
President And Chief Operating Officer |  |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |
Retention bonus |  |  |  | $ 1.0 |  |  |  |  |  |
President And Chief Operating Officer | Restricted Stock |  |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |
Total fair value of restricted shares that vested |  |  | $ 0.8 |  |  |  |  |  |  |
Granted (in shares) |  | 19,851 |  |  |  |  |  |  |  |
Vested (in shares) |  | 6,617 |  |  |  |  |  |  |  |
General Counsel, Senior Vice President Regulatory and Public Policy, and Corporate Secretary | Restricted Stock |  |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |
Granted (in shares) | 9,300 |  |  |  |  |  |  |  |  |
General Counsel, Senior Vice President Regulatory and Public Policy, and Corporate Secretary | Restricted Stock | Share-Based Payment Arrangement, Tranche One |  |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |
Vesting percentage | 50.00% |  |  |  |  |  |  |  |  |
General Counsel, Senior Vice President Regulatory and Public Policy, and Corporate Secretary | Restricted Stock | Share-Based Payment Arrangement, Tranche Two |  |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |
Vesting percentage | 50.00% |  |  |  |  |  |  |  |  |
Performance Equity Plan |  |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |
Vesting period for awards |  |  |  |  | 3 years |  |  |  |  |
Vesting rate (as a percent) |  |  |  |  | 100.00% |  |  |  |  |
Number of shares authorized (in shares) |  |  |  |  |  |  |  |  | 2,500,000 | 13,500,000
Charge to share pool for each share awarded |  |  |  |  | 5 |  |  |  |  |
Performance Equity Plan | Performance Shares |  |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |
Vesting period for awards |  |  |  |  | 3 years |  |  |  |  |
Performance Equity Plan | Nonemployee Members of the Board of Directors |  |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |
Vesting period for awards |  |  |  |  | 1 year |  |  |  |  |
Retention Agreement | Restricted Stock | Share-Based Payment Arrangement, Tranche One |  |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |
Vesting period for awards |  |  |  | 24 months |  |  |  |  |  |
Retention Agreement | Restricted Stock | Share-Based Payment Arrangement, Tranche Two |  |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |
Vesting period for awards |  |  |  | 6 months |  |  |  |  |  |
Retention Agreement | Chairman And Chief Executive Officer | Restricted Stock |  |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |
Nonvested (in shares) |  |  |  | 26,766 |  |  |  |  |  |
Retention Agreement | Senior Vice President And General Counsel | Restricted Stock |  |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |
Nonvested (in shares) |  |  |  | 8,922 |  |  |  |  |  |

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