Significant Accounting Policies and Responsibility for Financial Statements (Details) - USD ($) |
3 Months Ended | 9 Months Ended | ||||
|---|---|---|---|---|---|---|
Sep. 30, 2026 |
Jun. 30, 2026 |
Sep. 30, 2025 |
Jun. 30, 2025 |
Sep. 30, 2026 |
Sep. 30, 2025 |
|
| Dividends Payable [Line Items] | ||||||
| Payment defaults under agreements | $ 0 | $ 0 | ||||
| Dividends declared per common share (in dollars per share) | $ 0.4225 | $ 0.4225 | $ 0.4075 | $ 0.4075 | $ 1.2675 | $ 1.2225 |
| Dividends declared on common stock | $ 90,065,000 | $ 85,884,000 | $ 136,839,000 | $ 124,644,000 | ||
| TXNM | ||||||
| Dividends Payable [Line Items] | ||||||
| Equity contribution from parent | 0 | 0 | 0 | 250,000,000.0 | ||
| Dividends declared on common stock | 0 | 0 | 0 | 0 | ||
| Public Service Company of New Mexico | ||||||
| Dividends Payable [Line Items] | ||||||
| Equity contribution from parent | 0 | 0 | 105,000,000 | 0 | ||
| Dividends declared on common stock | $ 0 | $ 0 | $ 0 | $ 0 | ||