Construction Program and Jointly-Owned Electric Generating Plants - Construction Program and Jointly-Owned Electric Generating Plants (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2017 USD ($) generating_unit	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Jointly Owned Utility Plant Interests [Line Items]
Construction expenditures	$ 500,461	$ 600,076	$ 558,589
Plant in Service	7,238,285	6,944,534
Accumulated depreciation	(2,592,692)	(2,334,938)
Regulatory disallowance	27,036	15,011	167,471
Regulatory assets	$ 600,672	501,223
Operating lease, option term extensions	2 years
Public Service Company of New Mexico
Jointly Owned Utility Plant Interests [Line Items]
Construction expenditures	$ 309,142	445,464	404,840
Plant in Service	5,501,070	5,359,211
Accumulated depreciation	(2,029,534)	(1,809,528)
Regulatory disallowance	27,036	15,011	167,471
Regulatory assets	459,239	365,413
Public Service Company of New Mexico | Clean Air Act, SNCR
Jointly Owned Utility Plant Interests [Line Items]
Regulatory disallowance			21,600
Texas-New Mexico Power Company
Jointly Owned Utility Plant Interests [Line Items]
Construction expenditures	145,495	122,518	124,584
Plant in Service	1,504,778	1,380,584
Accumulated depreciation	(460,858)	(429,397)
Regulatory assets	141,433	135,810
Joint Projects | Public Service Company of New Mexico
Jointly Owned Utility Plant Interests [Line Items]
Construction expenditures	309,100
Joint Projects | Texas-New Mexico Power Company
Jointly Owned Utility Plant Interests [Line Items]
Construction expenditures	145,500
Joint Projects | PNMR
Jointly Owned Utility Plant Interests [Line Items]
Construction expenditures	$ 500,500
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	$ 920,950
Accumulated depreciation	(522,750)
Construction Work in Progress	$ 8,512
Composite Interest	46.30%
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	$ 918,830
Accumulated depreciation	(353,054)
Construction Work in Progress	$ 35,038
Composite Interest	10.20%
Period of time for the original full power operating licenses	40 years
Number of units (in generating units) | generating_unit	3
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	$ 204,432
Accumulated depreciation	(100,914)
Construction Work in Progress	$ 61,755
Composite Interest	13.00%
Luna (Gas) | Public Service Company of New Mexico
Jointly Owned Utility Plant Interests [Line Items]
Plant in Service	$ 70,995
Accumulated depreciation	(27,023)
Construction Work in Progress	$ (13)
Composite Interest	33.33%
San Juan Generating Station Units 2 and 3 | Public Service Company of New Mexico
Jointly Owned Utility Plant Interests [Line Items]
Plant in Service	$ 439,400	471,800	468,200
Accumulated depreciation	(188,300)	(203,900)	(193,300)
Construction Work in Progress			2,200
Net book value	251,100	$ 139,300	277,100
Regulatory assets	$ 125,500
San Juan Generating Station Units 2 and 3 | Public Service Company of New Mexico | Clean Air Act, SNCR
Jointly Owned Utility Plant Interests [Line Items]
Regulatory disallowance			$ 127,600
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%