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Regulatory and Rate Matters - TNMP Narrative (Details) advanced_meter in Thousands, $ in Thousands								1 Months Ended			12 Months Ended
	Feb. 05, 2021 USD ($)	Jun. 26, 2020 USD ($)	Apr. 06, 2020 USD ($)	Dec. 20, 2018 USD ($)	May 30, 2018 USD ($)	Jan. 10, 2018 USD ($)	Dec. 07, 2016 USD ($)	Oct. 31, 2019 USD ($)	Aug. 31, 2019 USD ($)	Jul. 31, 2011 USD ($)	Dec. 31, 2020 USD ($) advanced_meter	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Oct. 02, 2020 USD ($)	Jul. 27, 2020 USD ($)	May 29, 2020 USD ($)	Dec. 31, 2019 USD ($)
Public Utilities, General Disclosures [Line Items]
Net increase (decrease) in regulatory liabilities												$ 7,175
Public Service Company of New Mexico
Public Utilities, General Disclosures [Line Items]
Regulatory liabilities											$ 670,292						$ 683,769
Net increase (decrease) in regulatory liabilities												11,244
Texas-New Mexico Power Company
Public Utilities, General Disclosures [Line Items]
Regulatory liabilities											$ 187,407						182,979
Net increase (decrease) in regulatory liabilities												(4,069)
Refund of regulatory liability to customers													$ 37,800
Estimate of possible upgrades														$ 46,000
Energy efficiency cost recovery factor, requested change amount																$ 5,900
Energy efficiency cost recovery factor, requested performance bonus															$ 1,000	$ 1,000
Requested increase annual distribution revenue requirement			$ 14,700
Incremental distribution investments			$ 149,200
Annual distribution revenue requirement		$ 14,300
CTC Funding amount interest minimum											15.00%
Reduction to revenue												$ 5,400
Texas-New Mexico Power Company | 2018 TNMP Rate Case
Public Utilities, General Disclosures [Line Items]
Requested rate increase (decrease)				$ 10,000	$ 25,900
Requested return on equity				9.65%	10.50%
Requested cost of debt, percentage					7.20%
Requested debt capital structure, percentage				55.00%	50.00%
Requested equity capital structure, percentage				45.00%	50.00%
Regulatory liabilities													146,500
Net increase (decrease) in regulatory liabilities													$ 14,400
Refund of federal income tax rates period												3 years	5 years
Investments excluded from rate, amount				$ 10,600
Recovery of direct costs								$ 3,300	$ 3,800
Remaining recovery period of regulatory assets for which no return investment during recovery period is provided									3 years
Write off regulatory dissallowance																	$ 500
Texas-New Mexico Power Company | Advanced Meter System Deployment and Surcharge Request
Public Utilities, General Disclosures [Line Items]
Approved deployment costs										$ 113,400
Period of time to collect deployment costs through surcharge period										12 years
Number of advanced meters installed | advanced_meter											242
Texas-New Mexico Power Company | Transmission Cost of Service Rates | Subsequent Event
Public Utilities, General Disclosures [Line Items]
Requested rate increase (decrease)	$ 112,600
Requested increase in annual transmission service revenue	$ 14,100
NMPRC
Public Utilities, General Disclosures [Line Items]
Requested rate increase (decrease)							$ 99,200
Requested return on equity							10.125%
Proposed term for providing benefits to customers related to reduction in state corporate tax													23 years
NMPRC | Public Service Company of New Mexico
Public Utilities, General Disclosures [Line Items]
Requested rate increase (decrease)						$ 10,300
Requested return on equity						9.575%
Proposed term for providing benefits to customers related to reduction in state corporate tax						3 years

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