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Fair Value of Derivative and Other Financial Instruments - Available for Sale Securities (Details) - USD ($) $ in Thousands | 3 Months Ended |
--- | --- | ---
Mar. 31, 2016 | Mar. 31, 2015 | Dec. 31, 2015
Schedule of Available-for-sale Securities [Line Items] |  |  |
Other than temporary impairment losses, Investments, portion recognized in earnings, net, available-for-sale securities | $ 1,600 | $ 400 |
PNMR and PNM [Member] |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |
Fair Value | 260,628 |  | $ 259,042
Unrealized Gains | 22,980 |  | 28,820
Proceeds from sales | 124,900 | 31,852 |
Gross realized gains | 10,716 | 5,135 |
Gross realized (losses) | (6,116) | $ (1,541) |
PNMR and PNM [Member] | Fair Value, Measurements, Recurring [Member] |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |
Fair Value | 260,628 |  | 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 | 250,500 |  | 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 | 10,100 |  | 9,900
PNMR and PNM [Member] | Cash and equivalents [Member] |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |
Fair Value | 8,810 |  | 10,700
Unrealized Gains | 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 | 8,810 |  | 10,700
PNMR and PNM [Member] | Domestic value [Member] |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |
Fair Value | 62,427 |  | 44,505
Unrealized Gains | 10,862 |  | 11,610
PNMR and PNM [Member] | Domestic value [Member] | Fair Value, Measurements, Recurring [Member] |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |
Fair Value | 62,427 |  | 44,505
PNMR and PNM [Member] | Domestic growth [Member] |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |
Fair Value | 43,714 |  | 61,078
Unrealized Gains | 5,164 |  | 11,163
PNMR and PNM [Member] | Domestic growth [Member] | Fair Value, Measurements, Recurring [Member] |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |
Fair Value | 43,714 |  | 61,078
PNMR and PNM [Member] | International and other [Member] |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |
Fair Value | 27,937 |  | 27,961
Unrealized Gains | 2,034 |  | 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 | 27,937 |  | 27,961
PNMR and PNM [Member] | U.S. Government [Member] |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |
Fair Value | 37,203 |  | 27,880
Unrealized Gains | 563 |  | 178
PNMR and PNM [Member] | U.S. Government [Member] | Fair Value, Measurements, Recurring [Member] |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |
Fair Value | 37,203 |  | 27,880
PNMR and PNM [Member] | Municipals [Member] |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |
Fair Value | 50,276 |  | 58,576
Unrealized Gains | 2,839 |  | 3,672
PNMR and PNM [Member] | Municipals [Member] | Fair Value, Measurements, Recurring [Member] |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |
Fair Value | 50,276 |  | 58,576
PNMR and PNM [Member] | Corporate and other [Member] |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |
Fair Value | 30,261 |  | 28,342
Unrealized Gains | 1,518 |  | 628
PNMR and PNM [Member] | Corporate and other [Member] | Fair Value, Measurements, Recurring [Member] |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |
Fair Value | $ 30,261 |  | $ 28,342

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