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Fair Value of Derivative and Other Financial Instruments - Available for Sale Securities (Details) - USD ($) $ in Thousands | 3 Months Ended | 6 Months Ended |
--- | --- | --- | ---
Jun. 30, 2016 | Jun. 30, 2015 | Jun. 30, 2016 | Jun. 30, 2015 | Dec. 31, 2015
Schedule of Available-for-sale Securities [Line Items] |  |  |  |  |
(Increase)/Decrease in other than temporary losses, Investments, Portion Recognized in Earnings, Net, Available-for-sale Securities | $ (700) | $ (1,200) | $ 900 | $ (800) |
PNMR and PNM [Member] |  |  |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |  |  |
Fair Value | 264,669 |  | 264,669 |  | $ 259,042
Unrealized Gains | 21,988 |  | 21,988 |  | 28,820
Proceeds from sales | 69,115 | 62,670 | 194,014 | 94,522 |
Gross realized gains | 9,531 | 8,329 | 20,247 | 13,465 |
Gross realized (losses) | (4,233) | $ (1,578) | (10,349) | $ (3,119) |
PNMR and PNM [Member] | Fair Value, Measurements, Recurring [Member] |  |  |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |  |  |
Fair Value | 264,669 |  | 264,669 |  | 259,042
PNMR and PNM [Member] | Nuclear Decommissioning Trust [Member] | Fair Value, Measurements, Recurring [Member] |  |  |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |  |  |
Fair Value | 254,400 |  | 254,400 |  | 249,100
PNMR and PNM [Member] | Mine Reclamation Trust [Member] | Fair Value, Measurements, Recurring [Member] |  |  |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |  |  |
Fair Value | 10,300 |  | 10,300 |  | 9,900
PNMR and PNM [Member] | Cash and equivalents [Member] |  |  |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |  |  |
Fair Value | 3,535 |  | 3,535 |  | 10,700
Unrealized Gains | 0 |  | 0 |  | 0
PNMR and PNM [Member] | Cash and equivalents [Member] | Fair Value, Measurements, Recurring [Member] |  |  |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |  |  |
Fair Value | 3,535 |  | 3,535 |  | 10,700
PNMR and PNM [Member] | Domestic value [Member] |  |  |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |  |  |
Fair Value | 61,672 |  | 61,672 |  | 44,505
Unrealized Gains | 7,517 |  | 7,517 |  | 11,610
PNMR and PNM [Member] | Domestic value [Member] | Fair Value, Measurements, Recurring [Member] |  |  |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |  |  |
Fair Value | 61,672 |  | 61,672 |  | 44,505
PNMR and PNM [Member] | Domestic growth [Member] |  |  |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |  |  |
Fair Value | 45,484 |  | 45,484 |  | 61,078
Unrealized Gains | 4,977 |  | 4,977 |  | 11,163
PNMR and PNM [Member] | Domestic growth [Member] | Fair Value, Measurements, Recurring [Member] |  |  |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |  |  |
Fair Value | 45,484 |  | 45,484 |  | 61,078
PNMR and PNM [Member] | International and other [Member] |  |  |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |  |  |
Fair Value | 26,413 |  | 26,413 |  | 27,961
Unrealized Gains | 1,937 |  | 1,937 |  | 1,569
PNMR and PNM [Member] | International and other [Member] | Fair Value, Measurements, Recurring [Member] |  |  |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |  |  |
Fair Value | 26,413 |  | 26,413 |  | 27,961
PNMR and PNM [Member] | U.S. Government [Member] |  |  |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |  |  |
Fair Value | 38,263 |  | 38,263 |  | 27,880
Unrealized Gains | 1,293 |  | 1,293 |  | 178
PNMR and PNM [Member] | U.S. Government [Member] | Fair Value, Measurements, Recurring [Member] |  |  |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |  |  |
Fair Value | 38,263 |  | 38,263 |  | 27,880
PNMR and PNM [Member] | Municipals [Member] |  |  |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |  |  |
Fair Value | 56,078 |  | 56,078 |  | 58,576
Unrealized Gains | 3,843 |  | 3,843 |  | 3,672
PNMR and PNM [Member] | Municipals [Member] | Fair Value, Measurements, Recurring [Member] |  |  |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |  |  |
Fair Value | 56,078 |  | 56,078 |  | 58,576
PNMR and PNM [Member] | Corporate and other [Member] |  |  |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |  |  |
Fair Value | 33,224 |  | 33,224 |  | 28,342
Unrealized Gains | 2,421 |  | 2,421 |  | 628
PNMR and PNM [Member] | Corporate and other [Member] | Fair Value, Measurements, Recurring [Member] |  |  |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |  |  |
Fair Value | $ 33,224 |  | $ 33,224 |  | $ 28,342

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