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Income Taxes - Carryforwards (Details) - USD ($) $ in Thousands | 12 Months Ended |  |
--- | --- | --- | ---
Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2013 | Dec. 31, 2012
Operating Loss Carryforwards [Line Items] |  |  |  |  |
New Mexico corporate tax rate being phased in |  |  |  |  | 7.60%
New Mexico Corporate tax rate, effective by 2018 |  |  |  | 5.90% |
Regulatory liability |  | $ (10,109) | $ (7,132) |  |
Income tax expense |  | (1,259) | 712 |  |
Income Taxes, Impairment of Carryforwards |  |  |  |  |
State tax credit carryforwards | $ 0 | 0 | 0 |  |
State net operating loss carryforwards | 0 | 819 | (311) |  |
Charitable contribution carryforwards | 0 | 909 | 0 |  |
Compensation expense | 410 |  |  |  |
Income Taxes, Reserve Balances |  |  |  |  |
State tax credit carryforwards | 0 | 2,487 |  |  |
State net operating loss carryforwards | 0 | 1,131 |  |  |
Charitable contribution carryforwards | 0 | 952 |  |  |
Compensation expense | 410 |  |  |  |
Internal Revenue Service (IRS) |  |  |  |  |
Operating Loss Carryforwards [Line Items] |  |  |  |  |
Federal net operating loss carryforwards | 474,600 |  |  |  |
Federal tax credit carryforwards that expire beginning in 2023 | 76,500 |  |  |  |
Public Service Company of New Mexico |  |  |  |  |
Operating Loss Carryforwards [Line Items] |  |  |  |  |
Regulatory liability |  | (10,109) | (7,132) |  |
Income tax expense |  | (1,179) | 804 |  |
Income Taxes, Impairment of Carryforwards |  |  |  |  |
State tax credit carryforwards | 0 | 0 | 0 |  |
State net operating loss carryforwards | 0 | 627 | (213) |  |
Charitable contribution carryforwards | 0 | 0 | 0 |  |
Compensation expense | 298 |  |  |  |
Income Taxes, Reserve Balances |  |  |  |  |
State tax credit carryforwards | 0 | 0 |  |  |
State net operating loss carryforwards | 0 | 839 |  |  |
Charitable contribution carryforwards | 0 | 0 |  |  |
Compensation expense | 298 |  |  |  |
Texas-New Mexico Power Company |  |  |  |  |
Operating Loss Carryforwards [Line Items] |  |  |  |  |
Regulatory liability |  | 0 | 0 |  |
Income tax expense |  | 0 | 0 |  |
Income Taxes, Impairment of Carryforwards |  |  |  |  |
State tax credit carryforwards | 0 | 0 | 0 |  |
State net operating loss carryforwards | 0 | 0 | 0 |  |
Charitable contribution carryforwards | 0 | 0 | $ 0 |  |
Compensation expense | 111 |  |  |  |
Income Taxes, Reserve Balances |  |  |  |  |
State tax credit carryforwards | 0 | 0 |  |  |
State net operating loss carryforwards | 0 | 0 |  |  |
Charitable contribution carryforwards | 0 | $ 0 |  |  |
Compensation expense | 111 |  |  |  |
2015 Electric Rate Case | Public Service Company of New Mexico |  |  |  |  |
Income Taxes, Reserve Balances |  |  |  |  |
Approval to recover impairment of net operating loss carryforward | 2,100 |  |  |  |
Recovery period of regulatory asset |  | 2 years |  |  |
2016 Electric Rate Case | Public Service Company of New Mexico |  |  |  |  |
Income Taxes, Reserve Balances |  |  |  |  |
Approval to recover impairment of net operating loss carryforward | $ 3,300 |  |  |  |

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