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Goodwill (Details) - USD ($) $ in Thousands | Sep. 30, 2015 | Apr. 01, 2015 | Dec. 31, 2014 | Sep. 30, 2014 | Apr. 01, 2014 | Apr. 01, 2012
--- | --- | --- | --- | --- | --- | ---
Goodwill [Line Items] |  |  |  |  |  |
Goodwill | $ 278,297 |  | $ 278,297 | $ 278,297 |  |
Public Service Company of New Mexico [Member] |  |  |  |  |  |
Goodwill [Line Items] |  |  |  |  |  |
Goodwill |  | $ 51,600 |  |  | $ 51,600 |
Percentage of fair value in excess of carrying amount |  | 25.00% |  |  | 30.00% |
Texas-New Mexico Power Company [Member] |  |  |  |  |  |
Goodwill [Line Items] |  |  |  |  |  |
Goodwill |  |  |  |  |  | $ 226,700
Percentage of fair value in excess of carrying amount |  |  |  |  |  | 26.00%

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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 -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 + Details
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- Definition Percentage of fair value of reporting unit in excess of carrying amount. + References No definition available. + Details
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