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Goodwill (Details) - USD ($) $ in Thousands | 12 Months Ended |  |  |  |  |  |
--- | --- | --- | --- | --- | --- | --- | ---
Dec. 31, 2008 | Dec. 31, 2017 | Dec. 31, 2016 | Apr. 01, 2016 | Dec. 31, 2015 | Apr. 01, 2015 | Apr. 01, 2012
Schedule of Goodwill and Other Intangible Assets [Line Items] |  |  |  |  |  |  |
Goodwill |  | $ 278,297 | $ 278,297 |  | $ 278,297 |  |
Goodwill impairment | $ 174,400 |  |  |  |  |  |
Public Service Company of New Mexico |  |  |  |  |  |  |
Schedule of Goodwill and Other Intangible Assets [Line Items] |  |  |  |  |  |  |
Goodwill |  | 51,632 | 51,632 | $ 51,600 |  | $ 51,600 |
Percentage of fair value in excess of carrying amount |  |  |  | 25.00% |  |  |
Percentage increase in expected return on equity |  |  |  | 0.50% |  | 0.50% |
Reduced percentage of fair value in excess of carrying value |  |  |  | 18.00% |  |  |
Goodwill impairment | 51,100 |  |  |  |  |  |
Texas-New Mexico Power Company |  |  |  |  |  |  |
Schedule of Goodwill and Other Intangible Assets [Line Items] |  |  |  |  |  |  |
Goodwill |  | $ 226,665 | $ 226,665 | $ 226,700 |  |  |
Percentage of fair value in excess of carrying amount |  |  |  | 32.00% |  |  | 26.00%
Percentage increase in expected return on equity |  |  |  | 0.50% |  |  |
Reduced percentage of fair value in excess of carrying value |  |  |  | 21.00% |  |  |
Goodwill impairment | $ 34,500 |  |  |  |  |  |

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- Definition Goodwill, Reporting Unit, Sensitivity analysis, Percentage Increase in Expected Return on Equity + References No definition available. + Details
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- Definition Goodwill, Reporting Unit, Sensitivity analysis, Reduced Percentage of Fair Value in Excess of Carrying Value + References No definition available. + Details
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- Definition Amount after accumulated impairment loss of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=35741047&loc=d3e13816-109267 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 20 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6388280&loc=d3e13770-109266 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 20 -Section 45 -Paragraph 5 -URI http://asc.fasb.org/extlink&oid=77989000&loc=SL49117168-202975 + Details
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- Definition Amount of loss from the write-down of an asset representing the future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 20 -Section 50 -Paragraph 2 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=35741047&loc=d3e13854-109267 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 20 -Section 45 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=6388280&loc=d3e13777-109266 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3602-108585 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (e) -URI http://asc.fasb.org/extlink&oid=35741047&loc=d3e13816-109267 + Details
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