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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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