Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2017	Mar. 31, 2016
Equity [Abstract]
Percentage of pension liability adjustment capitalized into construction work In process	19.80%	22.70%
Percentage of pension liability adjustment capitalized into other accounts	5.40%	2.60%
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning Balance	$ (92,451)
Total Other Comprehensive Income (Loss)	3,993	$ (3,366)
Ending Balance	(88,458)
PNM
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning Balance	(92,428)	(71,476)
Amounts reclassified from AOCI (pre-tax)	(1,145)	(9,834)
Income tax impact of amounts reclassified	447	3,837
Other OCI changes (pre-tax)	7,766	5,458
Income tax impact of other OCI changes	(3,030)	(2,130)
Total Other Comprehensive Income (Loss)	4,038	(2,669)
Ending Balance	(88,390)	(74,145)
PNM \| Unrealized Gains on Available-for-Sale Securities
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning Balance	4,320	17,346
Amounts reclassified from AOCI (pre-tax)	(2,763)	(11,210)
Income tax impact of amounts reclassified	1,078	4,374
Other OCI changes (pre-tax)	7,766	5,458
Income tax impact of other OCI changes	(3,030)	(2,130)
Total Other Comprehensive Income (Loss)	3,051	(3,508)
Ending Balance	7,371	13,838
PNM \| Pension Liability Adjustment
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning Balance	(96,748)	(88,822)
Amounts reclassified from AOCI (pre-tax)	1,618	1,376
Income tax impact of amounts reclassified	(631)	(537)
Total Other Comprehensive Income (Loss)	987	839
Ending Balance	(95,761)	(87,983)
PNMR
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning Balance	(92,451)	(71,432)
Amounts reclassified from AOCI (pre-tax)	(1,033)	(9,688)
Income tax impact of amounts reclassified	403	3,780
Other OCI changes (pre-tax)	7,581	4,169
Income tax impact of other OCI changes	(2,958)	(1,627)
Total Other Comprehensive Income (Loss)	3,993	(3,366)
Ending Balance	(88,458)	(74,798)
PNMR \| Fair Value Adjustment for Cash Flow Hedges
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning Balance	(23)	44
Amounts reclassified from AOCI (pre-tax)	112	146
Income tax impact of amounts reclassified	(44)	(57)
Other OCI changes (pre-tax)	(185)	(1,289)
Income tax impact of other OCI changes	72	503
Total Other Comprehensive Income (Loss)	(45)	(697)
Ending Balance	$ (68)	$ (653)

Accumulated Other Comprehensive Income (Loss) [Roll Forward]

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Income tax impact of amounts reclassified from accumulated other comprehensive income

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Percentage of Pension Liability Adjustment Capitalized into Other Accounts

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Percentage of Pension Liability Adjustment Capitalized into Construction Work In Process

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Accumulated change in equity from transactions and other events and circumstances from non-owner sources, net of tax effect, at period end. Excludes Net Income (Loss), and accumulated changes in equity from transactions resulting from investments by owners and distributions to owners. Includes foreign currency translation items, certain pension adjustments, unrealized gains and losses on certain investments in debt and equity securities, other than temporary impairment (OTTI) losses related to factors other than credit losses on available-for-sale and held-to-maturity debt securities that an entity does not intend to sell and it is not more likely than not that the entity will be required to sell before recovery of the amortized cost basis, as well as changes in the fair value of derivatives related to the effective portion of a designated cash flow hedge.

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Amount before tax and reclassification adjustments of other comprehensive income (loss).

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Amount after tax and reclassification adjustments of other comprehensive income (loss).

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Amount of tax expense (benefit) allocated to other comprehensive income (loss).

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Amount before tax of reclassification adjustments of other comprehensive income (loss).

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