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Fair Value of Derivative and Other Financial Instruments - Items not Recorded at Fair Value (Details) - USD ($) $ in Thousands | Dec. 31, 2017 | Dec. 31, 2016
--- | --- | ---
PNMR |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Long-term debt | $ 2,554,836 | $ 2,540,693
Westmoreland Loan | 66,588 | 100,893
Other investments | 503 | 1,164
PNMR | Carrying Amount |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Long-term debt | 2,437,645 | 2,392,712
Westmoreland Loan | 56,640 | 95,000
Other investments | 503 | 547
PNMR | Quoted Prices in Active Markets for Identical Assets (Level 1) |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Long-term debt | 0 | 0
Westmoreland Loan | 0 | 0
Other investments | 503 | 547
PNMR | Significant Other Observable Inputs (Level 2) |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Long-term debt | 2,554,836 | 2,540,693
Westmoreland Loan | 0 | 0
Other investments | 0 | 0
PNMR | Significant Unobservable Inputs (Level 3) |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Long-term debt | 0 | 0
Westmoreland Loan | 66,588 | 100,893
Other investments | 0 | 617
Public Service Company of New Mexico |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Long-term debt | 1,727,135 | 1,730,157
Other investments | 283 | 316
Public Service Company of New Mexico | Carrying Amount |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Long-term debt | 1,657,910 | 1,631,369
Other investments | 283 | 316
Public Service Company of New Mexico | Quoted Prices in Active Markets for Identical Assets (Level 1) |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Long-term debt | 0 | 0
Other investments | 283 | 316
Public Service Company of New Mexico | Significant Other Observable Inputs (Level 2) |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Long-term debt | 1,727,135 | 1,730,157
Other investments | 0 | 0
Public Service Company of New Mexico | Significant Unobservable Inputs (Level 3) |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Long-term debt | 0 | 0
Other investments | 0 | 0
Texas-New Mexico Power Company |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Long-term debt | 527,563 | 468,329
Other investments | 220 | 231
Texas-New Mexico Power Company | Carrying Amount |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Long-term debt | 480,620 | 420,875
Other investments | 220 | 231
Texas-New Mexico Power Company | Quoted Prices in Active Markets for Identical Assets (Level 1) |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Long-term debt | 0 | 0
Other investments | 220 | 231
Texas-New Mexico Power Company | Significant Other Observable Inputs (Level 2) |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Long-term debt | 527,563 | 468,329
Other investments | 0 | 0
Texas-New Mexico Power Company | Significant Unobservable Inputs (Level 3) |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |
Long-term debt | 0 | 0
Other investments | $ 0 | $ 0

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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
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- Definition The fair value amount of long-term debt whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. + References No definition available. + Details
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- Definition Fair value portion of an agreement for an unconditional promise by the maker to pay the holder a definite sum of money at a future date. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.3(b)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
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