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Fair Value of Derivative and Other Financial Instruments - Items Recorded at Fair Value (Details) - PNMR and PNM - USD ($) $ in Thousands | 12 Months Ended
--- | ---
Dec. 31, 2018 | Dec. 31, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Fair value | $ 205,738 |
Measured on a recurring basis |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Fair value | 328,242 | $ 323,524
Unrealized Gains | 2,600 |
Measured on a recurring basis | Commodity Contract |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Commodity derivative assets | 3,594 | 4,644
Commodity derivative liabilities | (3,688) | (4,738)
Net | (94) | (94)
Measured on a recurring basis | Cash and cash equivalents |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Fair value | 11,472 | 52,636
Measured on a recurring basis | Domestic value |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Fair value | 32,997 | 40,032
Measured on a recurring basis | Domestic growth |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Fair value | 7,258 | 35,456
Measured on a recurring basis | International and other |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Fair value | 70,777 | 45,867
Measured on a recurring basis | U.S. Government |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Fair value | 29,503 | 34,317
Unrealized Gains | 1,098 |
Measured on a recurring basis | International Government |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Fair value | 8,435 |
Unrealized Gains | 90 |
Measured on a recurring basis | Municipals |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Fair value | 53,642 | 48,076
Unrealized Gains | 489 |
Measured on a recurring basis | Corporate and other |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Fair value | 114,158 | 67,140
Unrealized Gains | 923 |
Measured on a recurring basis | Quoted Prices in Active Markets for Identical Assets (Level 1) |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Fair value | 136,150 | 204,101
Measured on a recurring basis | Quoted Prices in Active Markets for Identical Assets (Level 1) | Commodity Contract |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Commodity derivative assets | 0 | 0
Commodity derivative liabilities | 0 | 0
Net | 0 | 0
Measured on a recurring basis | Quoted Prices in Active Markets for Identical Assets (Level 1) | Cash and cash equivalents |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Fair value | 11,472 | 52,636
Measured on a recurring basis | Quoted Prices in Active Markets for Identical Assets (Level 1) | Domestic value |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Fair value | 32,997 | 40,032
Measured on a recurring basis | Quoted Prices in Active Markets for Identical Assets (Level 1) | Domestic growth |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Fair value | 1,654 | 35,456
Measured on a recurring basis | Quoted Prices in Active Markets for Identical Assets (Level 1) | International and other |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Fair value | 70,777 | 42,332
Measured on a recurring basis | Quoted Prices in Active Markets for Identical Assets (Level 1) | U.S. Government |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Fair value | 18,662 | 33,645
Measured on a recurring basis | Quoted Prices in Active Markets for Identical Assets (Level 1) | International Government |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Fair value | 0 |
Measured on a recurring basis | Quoted Prices in Active Markets for Identical Assets (Level 1) | Municipals |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Fair value | 0 | 0
Measured on a recurring basis | Quoted Prices in Active Markets for Identical Assets (Level 1) | Corporate and other |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Fair value | 588 | 0
Measured on a recurring basis | Significant Other Observable Inputs (Level 2) |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Fair value | 189,936 | 119,423
Measured on a recurring basis | Significant Other Observable Inputs (Level 2) | Commodity Contract |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Commodity derivative assets | 3,594 | 4,644
Commodity derivative liabilities | (3,688) | (4,738)
Net | (94) | (94)
Measured on a recurring basis | Significant Other Observable Inputs (Level 2) | Cash and cash equivalents |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Fair value | 0 | 0
Measured on a recurring basis | Significant Other Observable Inputs (Level 2) | Domestic value |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Fair value | 0 | 0
Measured on a recurring basis | Significant Other Observable Inputs (Level 2) | Domestic growth |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Fair value | 5,604 | 0
Measured on a recurring basis | Significant Other Observable Inputs (Level 2) | International and other |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Fair value | 0 | 3,535
Measured on a recurring basis | Significant Other Observable Inputs (Level 2) | U.S. Government |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Fair value | 10,841 | 672
Measured on a recurring basis | Significant Other Observable Inputs (Level 2) | International Government |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Fair value | 8,435 |
Measured on a recurring basis | Significant Other Observable Inputs (Level 2) | Municipals |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Fair value | 53,642 | 48,076
Measured on a recurring basis | Significant Other Observable Inputs (Level 2) | Corporate and other |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Fair value | 111,414 | 67,140
Measured on a recurring basis | Significant Unobservable Inputs (Level 3) |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Fair value | 2,156 | 0
Unrealized Gains |  | 18,028
Measured on a recurring basis | Significant Unobservable Inputs (Level 3) | Commodity Contract |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Commodity derivative assets |  | 0
Commodity derivative liabilities |  | 0
Net |  | 0
Measured on a recurring basis | Significant Unobservable Inputs (Level 3) | Cash and cash equivalents |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Fair value | 0 | 0
Measured on a recurring basis | Significant Unobservable Inputs (Level 3) | Domestic value |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Fair value | 0 | 0
Unrealized Gains |  | 4,011
Measured on a recurring basis | Significant Unobservable Inputs (Level 3) | Domestic growth |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Fair value | 0 | 0
Unrealized Gains |  | 3,995
Measured on a recurring basis | Significant Unobservable Inputs (Level 3) | International and other |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Fair value | 0 | 0
Unrealized Gains |  | 6,810
Measured on a recurring basis | Significant Unobservable Inputs (Level 3) | U.S. Government |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Fair value | 0 | 0
Unrealized Gains |  | 273
Measured on a recurring basis | Significant Unobservable Inputs (Level 3) | International Government |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Fair value | 0 |
Measured on a recurring basis | Significant Unobservable Inputs (Level 3) | Municipals |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Fair value | 0 | 0
Unrealized Gains |  | 1,225
Measured on a recurring basis | Significant Unobservable Inputs (Level 3) | Corporate and other |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Fair value | $ 2,156 | 0
Unrealized Gains |  | $ 1,714

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