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Income Taxes - Reconciliation of Unrecognized Tax Benefits (Expense) (Details) - USD ($) $ in Thousands | 12 Months Ended
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Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016
PNMR |  |  |
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward] |  |  |
Beginning balance | $ 9,429 | $ 6,752 | $ 6,455
Additions based on tax positions | 543 | 262 | 242
Additions (reductions) for tax positions of prior years | 222 | 2,415 | 55
Settlement payments | 0 | 0 | 0
Ending balance | 10,194 | 9,429 | 6,752
Unrecognized tax benefits that would impact effective tax rate | 9,600 |  |
Public Service Company of New Mexico |  |  |
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward] |  |  |
Beginning balance | 6,563 | 3,949 | 3,652
Additions based on tax positions | 543 | 262 | 242
Additions (reductions) for tax positions of prior years | 182 | 2,352 | 55
Settlement payments | 0 | 0 | 0
Ending balance | 7,288 | 6,563 | 3,949
Unrecognized tax benefits that would impact effective tax rate | 6,700 |  |
Texas-New Mexico Power Company |  |  |
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward] |  |  |
Beginning balance | 63 | 0 |
Additions based on tax positions | 0 | 0 | 0
Additions (reductions) for tax positions of prior years | 40 | 63 | 0
Settlement payments | 0 | 0 | 0
Ending balance | 103 | $ 63 | $ 0
Unrecognized tax benefits that would impact effective tax rate | $ 100 |  |

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- Definition A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period. + References No definition available. + Details
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- Definition Amount of unrecognized tax benefits. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 45 -Paragraph 10B -URI http://asc.fasb.org/extlink&oid=84176650&loc=SL37586934-109318 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 15A -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=84230637&loc=SL6600010-109319 + Details
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- Definition Amount of decrease in unrecognized tax benefits resulting from settlements with taxing authorities. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 15A -Subparagraph (a)(3) -URI http://asc.fasb.org/extlink&oid=84230637&loc=SL6600010-109319 + Details
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- Definition Amount of increase in unrecognized tax benefits resulting from tax positions that have been or will be taken in current period tax return. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 15A -Subparagraph (a)(2) -URI http://asc.fasb.org/extlink&oid=84230637&loc=SL6600010-109319 + Details
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- Definition Amount of increase in unrecognized tax benefits resulting from tax positions taken in prior period tax returns. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 15A -Subparagraph (a)(1) -URI http://asc.fasb.org/extlink&oid=84230637&loc=SL6600010-109319 + Details
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