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Construction Program and Jointly-Owned Electric Generating Plants - Construction Program and Jointly-Owned Electric Generating Plants (Details) $ in Thousands | 12 Months Ended |  |
--- | --- | --- | ---
Dec. 31, 2018 USD ($) generating_unit MW | Dec. 31, 2017 USD ($) | Dec. 31, 2016 USD ($) | Dec. 16, 2015 MW | Jul. 31, 2015 MW
Jointly Owned Utility Plant Interests [Line Items] |  |  |  |  |
Construction expenditures | $ 501,213 | $ 500,461 | $ 600,076 |  |
Plant in Service | 7,548,581 | 7,238,285 |  |  |
Accumulated depreciation | $ (2,604,177) | (2,592,692) |  |  |
Operating lease, option term extensions | 2 years |  |  |  |
Public Service Company of New Mexico |  |  |  |  |
Jointly Owned Utility Plant Interests [Line Items] |  |  |  |  |
Construction expenditures | $ 255,627 | 309,142 | 445,464 |  |
Plant in Service | 5,623,520 | 5,501,070 |  |  |
Accumulated depreciation | (2,006,266) | (2,029,534) |  |  |
Texas-New Mexico Power Company |  |  |  |  |
Jointly Owned Utility Plant Interests [Line Items] |  |  |  |  |
Construction expenditures | 223,448 | 145,495 | $ 122,518 |  |
Plant in Service | 1,686,119 | 1,504,778 |  |  |
Accumulated depreciation | (487,734) | $ (460,858) |  |  |
Joint Projects | Public Service Company of New Mexico |  |  |  |  |
Jointly Owned Utility Plant Interests [Line Items] |  |  |  |  |
Construction expenditures | 255,600 |  |  |  |
Joint Projects | Texas-New Mexico Power Company |  |  |  |  |
Jointly Owned Utility Plant Interests [Line Items] |  |  |  |  |
Construction expenditures | 223,400 |  |  |  |
Joint Projects | PNMR |  |  |  |  |
Jointly Owned Utility Plant Interests [Line Items] |  |  |  |  |
Construction expenditures | 501,200 |  |  |  |
San Juan Generating Station Unit 4 | Public Service Company of New Mexico |  |  |  |  |
Jointly Owned Utility Plant Interests [Line Items] |  |  |  |  |
Pre-tax impairment of investments | 121,800 |  |  |  |
San Juan Generating Station Unit 4 | Texas-New Mexico Power Company |  |  |  |  |
Jointly Owned Utility Plant Interests [Line Items] |  |  |  |  |
Pre-tax impairment of investments | $ 86,800 |  |  |  |
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 | $ 814,738 |  |  |  |
Accumulated depreciation | (443,517) |  |  |  |
Construction Work in Progress | $ 820 |  |  |  |
Composite Interest | 66.34% |  |  |  |
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 | $ 831,663 |  |  |  |
Accumulated depreciation | (365,708) |  |  |  |
Construction Work in Progress | $ 39,393 |  |  |  |
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 | Public Service Company of New Mexico |  |  |  |  |
Jointly Owned Utility Plant Interests [Line Items] |  |  |  |  |
Number of units (in generating units) | generating_unit | 2 |  |  |  |
Four Corners Units 4 and 5 (Coal) | Public Service Company of New Mexico |  |  |  |  |
Jointly Owned Utility Plant Interests [Line Items] |  |  |  |  |
Plant in Service | $ 276,960 |  |  |  |
Accumulated depreciation | (98,085) |  |  |  |
Construction Work in Progress | $ 7,455 |  |  |  |
Composite Interest | 13.00% |  |  |  |
Luna (Gas) | Public Service Company of New Mexico |  |  |  |  |
Jointly Owned Utility Plant Interests [Line Items] |  |  |  |  |
Plant in Service | $ 74,813 |  |  |  |
Accumulated depreciation | (28,609) |  |  |  |
Construction Work in Progress | $ 131 |  |  |  |
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% |  |  |  |
Clean Air Act, SNCR Hearing Examiner Recommended Denial | San Juan Generating Station Unit 4 | Public Service Company of New Mexico |  |  |  |  |
Jointly Owned Utility Plant Interests [Line Items] |  |  |  |  |
Additional ownership to be obtained (in megawatts) | MW | 132 |  |  | 132 |
Clean Air Act, SNCR | San Juan Generating Station Unit 4 | Public Service Company of New Mexico |  |  |  |  |
Jointly Owned Utility Plant Interests [Line Items] |  |  |  |  |
Additional ownership to be obtained (in megawatts) | MW | 65 |  |  | 65 | 132
Pre-tax impairment of investments | $ 35,000 |  |  |  |

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