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Pension and Other Postretirement Benefits - Other Postretirement Benefits (Details) - USD ($) $ in Thousands | 12 Months Ended
--- | ---
Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018
401(k) plan |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Abstract] |  |  |
401(k) plan | $ 16,247 | $ 16,097 | $ 16,677
401(k) plan | Public Service Company of New Mexico |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Abstract] |  |  |
401(k) plan | 11,676 | 11,587 | 12,052
401(k) plan | Texas-New Mexico Power Company |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Abstract] |  |  |
401(k) plan | 4,572 | 4,511 | 4,625
Non-qualified plan |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Abstract] |  |  |
Non-qualified plan | 2,090 | 4,551 | 865
Non-qualified plan | Public Service Company of New Mexico |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Abstract] |  |  |
Non-qualified plan | 1,544 | 3,384 | 621
Non-qualified plan | Texas-New Mexico Power Company |  |  |
Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Abstract] |  |  |
Non-qualified plan | $ 547 | $ 1,167 | $ 244

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