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Income Taxes - Schedule of Deferred Income Tax Components (Details) - USD ($) $ in Thousands | 12 Months Ended
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Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018
Income Taxes [Line Items] |  |  |
Net change in deferred income tax liability per above table | $ 68,454 |  |
Change in tax effects of income tax related regulatory assets and liabilities | (11,602) |  |
Amortization of excess deferred income tax | (30,723) |  |
Tax effect of mark-to-market adjustments | (3,206) |  |
Tax effect of excess pension liability | (3,670) |  |
Adjustment for uncertain income tax positions | 2,459 |  |
Reclassification of unrecognized tax benefits | (2,459) |  |
Amortization of state net operating loss recovered in prior years | 1,367 |  |
Refundable alternative minimum tax credit carryforward reclassified to receivable | 0 |  |
Other | (215) |  |
Deferred income taxes (benefits) | 20,405 | $ (25,385) | $ 8,019
Public Service Company of New Mexico |  |  |
Income Taxes [Line Items] |  |  |
Net change in deferred income tax liability per above table | 57,160 |  |
Change in tax effects of income tax related regulatory assets and liabilities | (7,936) |  |
Amortization of excess deferred income tax | (21,609) |  |
Tax effect of mark-to-market adjustments | (3,325) |  |
Tax effect of excess pension liability | (3,670) |  |
Adjustment for uncertain income tax positions | 2,454 |  |
Reclassification of unrecognized tax benefits | (1,999) |  |
Amortization of state net operating loss recovered in prior years | 1,367 |  |
Other | 0 |  |
Deferred income taxes (benefits) | 22,442 | (20,145) | 3,334
Texas-New Mexico Power Company |  |  |
Income Taxes [Line Items] |  |  |
Net change in deferred income tax liability per above table | 5,218 |  |
Change in tax effects of income tax related regulatory assets and liabilities | (3,666) |  |
Amortization of excess deferred income tax | (9,113) |  |
Other | (212) |  |
Deferred income taxes (benefits) | $ (7,773) | $ (7,650) | $ 1,780

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