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Construction Program and Jointly-Owned Electric Generating Plants (Details) $ in Thousands | 12 Months Ended
--- | ---
Dec. 31, 2020 USD ($) generating_unit | Dec. 31, 2019 USD ($) | Dec. 31, 2018 USD ($)
Jointly Owned Utility Plant Interests [Line Items] |  |  |
Construction expenditures | $ 679,028 | $ 616,273 | $ 501,213
Plant in Service | 8,480,799 | 7,918,601 |
Accumulated depreciation | (2,835,170) | (2,713,503) |
Public Service Company of New Mexico |  |  |
Jointly Owned Utility Plant Interests [Line Items] |  |  |
Construction expenditures | 335,055 | 341,847 | 255,627
Plant in Service | 6,022,753 | 5,753,267 |
Accumulated depreciation | (2,158,915) | (2,076,291) |
Texas-New Mexico Power Company |  |  |
Jointly Owned Utility Plant Interests [Line Items] |  |  |
Construction expenditures | 321,505 | 254,006 | $ 223,448
Plant in Service | 2,193,270 | 1,919,256 |
Accumulated depreciation | (537,707) | $ (516,795) |
Joint Projects | Public Service Company of New Mexico |  |  |
Jointly Owned Utility Plant Interests [Line Items] |  |  |
Construction expenditures | 335,100 |  |
Joint Projects | Texas-New Mexico Power Company |  |  |
Jointly Owned Utility Plant Interests [Line Items] |  |  |
Construction expenditures | 321,500 |  |
Joint Projects | PNMR |  |  |
Jointly Owned Utility Plant Interests [Line Items] |  |  |
Construction expenditures | $ 679,000 |  |
SJGS (Coal) | Unit 4 | Other Unrelated Entities 2 |  |  |
Jointly Owned Utility Plant Interests [Line Items] |  |  |
Jointly owned utility plant, ownership percentage | 12.80% |  |
SJGS (Coal) | Unit 4 | Other Unrelated Entities 3 |  |  |
Jointly Owned Utility Plant Interests [Line Items] |  |  |
Jointly owned utility plant, ownership percentage | 8.475% |  |
SJGS (Coal) | Unit 4 | Other Unrelated Entities 4 |  |  |
Jointly Owned Utility Plant Interests [Line Items] |  |  |
Jointly owned utility plant, ownership percentage | 7.20% |  |
SJGS (Coal) | Unit 4 | Other Unrelated Entities 5 |  |  |
Jointly Owned Utility Plant Interests [Line Items] |  |  |
Jointly owned utility plant, ownership percentage | 7.028% |  |
SJGS (Coal) | Public Service Company of New Mexico |  |  |
Jointly Owned Utility Plant Interests [Line Items] |  |  |
Plant in Service | $ 780,544 |  |
Accumulated depreciation | (448,213) |  |
Construction Work in Progress | $ 659 |  |
Composite Interest | 66.35% |  |
SJGS (Coal) | Public Service Company of New Mexico | Unit 4 |  |  |
Jointly Owned Utility Plant Interests [Line Items] |  |  |
Composite Interest | 77.297% |  |
Palo Verde Nuclear Generating Station | Public Service Company of New Mexico |  |  |
Jointly Owned Utility Plant Interests [Line Items] |  |  |
Plant in Service | $ 828,191 |  |
Accumulated depreciation | (387,436) |  |
Construction Work in Progress | $ 37,235 |  |
Composite Interest | 10.20% |  |
Number of units (in generating units) | generating_unit | 3 |  |
Period of time for the original full power operating licenses | 40 years |  |
Operating lease, option term extensions | 20 years |  |
Four Corners Units 4 and 5 (Coal) | Public Service Company of New Mexico |  |  |
Jointly Owned Utility Plant Interests [Line Items] |  |  |
Plant in Service | $ 301,867 |  |
Accumulated depreciation | (100,187) |  |
Construction Work in Progress | $ 7,820 |  |
Composite Interest | 13.00% |  |
Luna (Gas) | Public Service Company of New Mexico |  |  |
Jointly Owned Utility Plant Interests [Line Items] |  |  |
Plant in Service | $ 76,917 |  |
Accumulated depreciation | (29,758) |  |
Construction Work in Progress | $ 57 |  |
Composite Interest | 33.33% |  |
SJGS Units 1 and 2 | Other Unrelated Entities 1 |  |  |
Jointly Owned Utility Plant Interests [Line Items] |  |  |
Composite Interest | 50.00% |  |
SJGS Units 1 and 2 | Public Service Company of New Mexico |  |  |
Jointly Owned Utility Plant Interests [Line Items] |  |  |
Composite Interest | 50.00% |  |
Four Corners | Public Service Company of New Mexico |  |  |
Jointly Owned Utility Plant Interests [Line Items] |  |  |
Number of units (in generating units) | generating_unit | 2 |  |

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