Income Taxes - Carryforwards (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2013	Dec. 31, 2012
Operating Loss Carryforwards [Line Items]
New Mexico corporate tax rate being phased in					7.60%
New Mexico Corporate tax rate, effective by 2018				5.90%
Regulatory liability			$ (10,109)
Income tax expense			(1,259)
Income Taxes, Impairment of Carryforwards
State tax credit carryforwards	$ 425	$ 0	0
State net operating loss carryforwards	0	0	819
Charitable contribution carryforwards	0	0	909
Compensation expense	(99)	410
Income Taxes, Reserve Balances
State tax credit carryforwards	425	0
State net operating loss carryforwards	0	0
Charitable contribution carryforwards	0	0
Compensation expense	311	410
Internal Revenue Service (IRS)
Operating Loss Carryforwards [Line Items]
Federal net operating loss carryforwards	286,600
Federal tax credit carryforwards that expire beginning in 2023	101,200
Public Service Company of New Mexico
Operating Loss Carryforwards [Line Items]
Regulatory liability			(10,109)
Income tax expense			(1,179)
Income Taxes, Impairment of Carryforwards
State tax credit carryforwards	0	0	0
State net operating loss carryforwards	0	0	627
Charitable contribution carryforwards	0	0	0
Compensation expense	(100)	298
Income Taxes, Reserve Balances
State tax credit carryforwards	0	0
State net operating loss carryforwards	0	0
Charitable contribution carryforwards	0	0
Compensation expense	198	298
Texas-New Mexico Power Company
Operating Loss Carryforwards [Line Items]
Regulatory liability			0
Income tax expense			0
Income Taxes, Impairment of Carryforwards
State tax credit carryforwards	0	0	0
State net operating loss carryforwards	0	0	0
Charitable contribution carryforwards	0	0	$ 0
Compensation expense	2	111
Income Taxes, Reserve Balances
State tax credit carryforwards	0	0
State net operating loss carryforwards	0	0
Charitable contribution carryforwards	0	0
Compensation expense	$ 113	$ 111