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Regulatory and Rate Matters - COVID-19 Regulatory Matters (Details) - USD ($) $ in Thousands	Feb. 03, 2021	Dec. 31, 2020	Dec. 31, 2019
Public Utilities, General Disclosures [Line Items]
Regulatory assets		$ 557,790	$ 556,930
Regulatory liabilities		850,228	866,243
Public Service Company of New Mexico
Public Utilities, General Disclosures [Line Items]
Regulatory assets		457,953	435,467
Regulatory liabilities		664,873	683,398
Public Service Company of New Mexico | COVID-19 cost savings
Public Utilities, General Disclosures [Line Items]
Regulatory liabilities		900	0
COVID-19 | Public Service Company of New Mexico | COVID-19 cost savings
Public Utilities, General Disclosures [Line Items]
Regulatory liabilities		900
Deferred COVID-19 costs | Public Service Company of New Mexico
Public Utilities, General Disclosures [Line Items]
Regulatory assets		8,761	$ 0
Deferred COVID-19 costs | COVID-19 | Public Service Company of New Mexico
Public Utilities, General Disclosures [Line Items]
Regulatory assets		$ 8,800
COVID-19 | Subsequent Event
Public Utilities, General Disclosures [Line Items]
Temporary mandatory moratorium on disconnection period	100 days
Disconnection transition period	90 days

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Carrying amount as of the balance sheet date of capitalized costs of regulated entities that are not expected to be recovered through revenue sources within one year or the normal operating cycle if longer.

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 980
-SubTopic 340
-Section 50
-Paragraph 1
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The amount for the individual regulatory noncurrent liability as itemized in a table of regulatory noncurrent liabilities as of the end of the period.

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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.24)
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