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Regulatory and Rate Matters - COVID-19 Regulatory Matters (Details) - USD ($) $ in Thousands | Feb. 03, 2021 | Dec. 31, 2020 | Dec. 31, 2019
--- | --- | --- | ---
Public Utilities, General Disclosures [Line Items] |  |  |
Regulatory assets |  | $ 557,790 | $ 556,930
Regulatory liabilities |  | 850,228 | 866,243
Public Service Company of New Mexico |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |
Regulatory assets |  | 457,953 | 435,467
Regulatory liabilities |  | 664,873 | 683,398
Public Service Company of New Mexico | COVID-19 cost savings |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |
Regulatory liabilities |  | 900 | 0
COVID-19 | Public Service Company of New Mexico | COVID-19 cost savings |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |
Regulatory liabilities |  | 900 |
Deferred COVID-19 costs | Public Service Company of New Mexico |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |
Regulatory assets |  | 8,761 | $ 0
Deferred COVID-19 costs | COVID-19 | Public Service Company of New Mexico |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |
Regulatory assets |  | $ 8,800 |
COVID-19 | Subsequent Event |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |
Temporary mandatory moratorium on disconnection period | 100 days |  |
Disconnection transition period | 90 days |  |

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