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Regulatory and Rate Matters - COVID-19 Electricity Relief Program (Details) - Texas-New Mexico Power Company $ in Thousands | Apr. 14, 2020 USD ($) | Dec. 31, 2020 USD ($) | Mar. 30, 2020 MWh | Dec. 31, 2019 USD ($)
--- | --- | --- | --- | ---
Public Utilities, General Disclosures [Line Items] |  |  |  |
Rider charge from electricity relief program | MWh |  |  | 0.33 |
Regulatory liabilities |  | $ 187,407 |  | $ 182,979
Proceeds from short-term debt | $ 500 |  |  |
COVID-19 |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |
Regulatory liabilities |  | 100 |  |
Other deferred costs, gross, CARES Act |  | $ 700 |  |

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