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Fair Value of Derivative and Other Financial Instruments - Effect of Mark-to-Market Instruments on Earnings (Details) - PNMR and PNM - Designated as hedging instrument - Commodity Contract - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss)	$ (235)	$ (1,261)	$ 6,863
Electric operating revenues
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss)	5,151	(53)	7,156
Cost of energy
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss)	$ (5,386)	$ (1,208)	$ (293)

X

- Definition

Amount of increase (decrease) in the fair value of derivatives recognized in the income statement.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4A
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=84234895&loc=SL5618551-113959

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4C
-Subparagraph (a),(c),(d),(e)
-URI http://asc.fasb.org/extlink&oid=84234895&loc=SL5624171-113959

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- Definition

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+ References

No definition available.

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