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Financing - Financing Activities - TXNM (Narrative) (Details) |  |  |  |  |  |  |  |  |  | 3 Months Ended | 12 Months Ended |
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Dec. 31, 2024 USD ($) $ / shares shares | Dec. 30, 2024 shares | Aug. 05, 2024 USD ($) $ / shares | Jun. 21, 2024 USD ($) | Jun. 10, 2024 USD ($) d deferralPayment $ / shares | Jun. 04, 2024 | May 06, 2024 USD ($) $ / shares | Jun. 30, 2023 USD ($) | Nov. 10, 2022 USD ($) $ / shares | Dec. 31, 2024 USD ($) $ / shares shares | Sep. 30, 2024 $ / shares shares | Jun. 30, 2024 $ / shares shares | Dec. 31, 2024 USD ($) $ / shares shares | Dec. 31, 2023 $ / shares shares | Dec. 31, 2022 USD ($)
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Common stock, no par value (in dollars per share) | $ / shares | $ 0 |  |  |  |  |  |  |  |  | $ 0 |  |  | $ 0 | $ 0 |
Forward contracts, issuance costs |  |  |  |  |  |  |  |  |  |  |  |  | $ 1,000,000 |  |
Forward contracts, net cash proceeds | $ 198,200,000 |  |  |  |  |  |  |  |  | $ 198,200,000 |  |  | $ 198,200,000 |  |
Shares (in shares) | shares |  |  |  |  |  |  |  |  |  | 1,104,641 | 2,196,926 | 262,025 | 2,458,951 | 4,365,510 |
Initial forward price (in dollars per share) | $ / shares |  |  |  |  |  |  |  |  |  | $ 44.83 | $ 40.58 | $ 37.77 |  |  |
TXNM 2022 ATM Program |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Distribution agreement, aggregate value |  |  |  |  |  |  |  |  | $ 200,000,000 |  |  |  |  |  |
Common stock, no par value (in dollars per share) | $ / shares |  |  |  |  |  |  |  |  | $ 0 |  |  |  |  |  |
TXNM 2024 ATM Program |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Distribution agreement, aggregate value |  |  | $ 300,000,000 |  |  |  | $ 100,000,000 |  |  |  |  |  |  |  |
Common stock, no par value (in dollars per share) | $ / shares |  |  | $ 0 |  |  |  | $ 0 |  |  |  |  |  |  |  |
Forward contracts, issuance costs |  |  |  |  |  |  |  |  |  |  |  |  | $ 800,000 |  |
Forward contracts, net cash proceeds | $ 98,600,000 |  |  |  |  |  |  |  |  | $ 98,600,000 |  |  | $ 98,600,000 |  |
Shares (in shares) | shares | 1,104,641 | 2,458,951 |  |  |  |  |  |  |  |  |  |  |  |  |
TXNM 2021 Delayed-Draw Term Loan due May 2025 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Repayments of debt |  |  |  | $ 449,000,000 |  |  |  | $ 500,000,000 |  |  |  |  |  |  |
TXNM 2021 Delayed-Draw Term Loan due May 2025 | Bonds | TXNM |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Aggregate principal amount |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 1,000,000,000
TXNM 2021 Delayed-Draw Term Loan due May 2025 | Line of Credit | Revolving Credit Facility |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Interest rates on outstanding borrowings (as a percent) | 5.41% |  |  |  |  |  |  |  |  | 5.41% |  |  | 5.41% |  |
TXNM 2023 Term Loan |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Repayments of debt |  |  |  | 90,000,000 |  |  |  |  |  |  |  |  |  |  |
TXNM 2023 Term Loan | Line of Credit | Revolving Credit Facility |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Repayments of debt |  |  |  | 90,000,000 |  |  |  |  |  |  |  |  |  |  |
TXNM 2023 Term Loan | Secured Debt |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Aggregate principal amount |  |  |  |  |  |  |  | $ 500,000,000 |  |  |  |  |  |  |
Variable rate (as a percent) | 5.81% |  |  |  |  |  |  |  |  |  |  |  |  |  |
Five Point Seven Five Percent, Convertible Notes Due June Twenty Fifty Four | Convertible Debt |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Aggregate principal amount |  |  |  |  | $ 500,000,000 |  |  |  |  |  |  |  |  |  |
Stated percentage (as a percent) |  |  |  |  | 5.75% |  |  |  |  |  |  |  |  |  |
Conversion ratio |  |  |  |  |  | 0.0224911 |  |  |  |  |  |  |  |  |
Conversion price (in dollars per share) | $ / shares |  |  |  |  | $ 44.46 |  |  |  |  |  |  |  |  |  |
Conversion premium (as a percent) |  |  |  |  |  | 17.50% |  |  |  |  |  |  |  |  |
Number of deferral payments allowed | deferralPayment |  |  |  |  | 20 |  |  |  |  |  |  |  |  |  |
Five Point Seven Five Percent, Convertible Notes Due June Twenty Fifty Four | Convertible Debt | Debt Conversion Terms One |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Redemption price (as a percent) |  |  |  |  | 100.00% |  |  |  |  |  |  |  |  |  |
Five Point Seven Five Percent, Convertible Notes Due June Twenty Fifty Four | Convertible Debt | Debt Conversion Terms Two |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Redemption price (as a percent) |  |  |  |  | 100.00% |  |  |  |  |  |  |  |  |  |
Threshold stock price trigger (as a percent) |  |  |  |  | 130.00% |  |  |  |  |  |  |  |  |  |
Threshold trading days | d |  |  |  |  | 20 |  |  |  |  |  |  |  |  |  |
Threshold consecutive trading days | d |  |  |  |  | 30 |  |  |  |  |  |  |  |  |  |
Five Point Seven Five Percent, Convertible Notes Due June Twenty Fifty Four - Option | Convertible Debt |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Aggregate principal amount |  |  |  | 50,000,000 |  |  |  |  |  |  |  |  |  |  |
TXNM 2021 Delayed Draw Term Loan | Line of Credit | Revolving Credit Facility |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Repayments of debt |  |  |  | $ 449,000,000 |  |  |  |  |  |  |  |  |  |  |

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