Segment Information - Schedule (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Segment Reporting Information [Line Items]
Electric Operating Revenues	$ 332,605	$ 419,900	$ 362,320	$ 330,178	$ 336,225	$ 400,374	$ 315,391	$ 310,961	$ 1,445,003	$ 1,362,951	$ 1,439,082
Cost of energy									407,479	380,596	464,649
Utility margin									1,037,524	982,355	974,433
Other operating expenses									499,097	495,260	664,164
Depreciation and amortization									231,942	209,110	185,919
Operating income	22,936	142,484	85,105	55,960	63,584	108,071	64,822	41,508	306,485	277,985	124,350
Interest income									15,916	22,293	6,498
Other income (deductions)									30,983	23,529	30,165
Interest charges									(127,625)	(128,633)	(114,860)
Earnings before Income Taxes									225,759	195,174	46,153
Income taxes									130,340	63,278	15,075
Net Earnings	(50,585)	$ 78,327	$ 41,231	$ 26,446	28,423	$ 58,556	$ 30,952	$ 13,965	95,419	131,896	31,078
Valencia non-controlling interest									(15,017)	(14,519)	(14,910)
Subsidiary preferred stock dividends									(528)	(528)	(528)
Segment earnings (loss) attributable to PNMR									79,874	116,849	15,640
Total Assets	6,646,103				6,471,080				6,646,103	6,471,080	6,009,328
Goodwill	278,297				278,297				278,297	278,297	278,297
PNM
Segment Reporting Information [Line Items]
Electric Operating Revenues									1,104,230	1,035,913	1,131,195
Cost of energy									321,677	299,714	391,131
Utility margin									782,553	736,199	740,064
Other operating expenses									423,011	414,662	590,967
Depreciation and amortization									147,017	133,447	115,717
Operating income									212,525	188,090	33,380
Interest income									8,454	10,173	6,574
Other income (deductions)									30,686	22,066	26,914
Interest charges									(82,697)	(87,469)	(79,950)
Earnings before Income Taxes									168,968	132,860	(13,082)
Income taxes									81,555	40,922	(12,758)
Net Earnings									87,413	91,938	(324)
Valencia non-controlling interest									(15,017)	(14,519)	(14,910)
Subsidiary preferred stock dividends									(528)	(528)	(528)
Segment earnings (loss) attributable to PNMR									71,868	76,891	(15,762)
Total Assets	4,921,563				4,867,546				4,921,563	4,867,546	4,599,344
Goodwill	51,632				51,632				51,632	51,632	51,632
TNMP
Segment Reporting Information [Line Items]
Electric Operating Revenues									340,773	327,038	307,887
Cost of energy									85,802	80,882	73,518
Utility margin									254,971	246,156	234,369
Other operating expenses									98,221	93,389	88,051
Depreciation and amortization									63,146	61,126	56,285
Operating income									93,604	91,641	90,033
Interest income									0	0	0
Other income (deductions)									3,551	3,202	3,736
Interest charges									(30,084)	(29,335)	(27,681)
Earnings before Income Taxes									67,071	65,508	66,088
Income taxes									31,512	23,836	24,125
Net Earnings									35,559	41,672	41,963
Valencia non-controlling interest									0	0	0
Subsidiary preferred stock dividends									0	0	0
Segment earnings (loss) attributable to PNMR									35,559	41,672	41,963
Total Assets	1,500,770				1,383,223				1,500,770	1,383,223	1,297,139
Goodwill	226,665				226,665				226,665	226,665	226,665
Corporate and Other
Segment Reporting Information [Line Items]
Electric Operating Revenues									0	0	0
Cost of energy									0	0	0
Utility margin									0	0	0
Other operating expenses									(22,135)	(12,791)	(14,854)
Depreciation and amortization									21,779	14,537	13,917
Operating income									356	(1,746)	937
Interest income									7,462	12,120	(76)
Other income (deductions)									(3,254)	(1,739)	(485)
Interest charges									(14,844)	(11,829)	(7,229)
Earnings before Income Taxes									(10,280)	(3,194)	(6,853)
Income taxes									17,273	(1,480)	3,708
Net Earnings									(27,553)	(1,714)	(10,561)
Valencia non-controlling interest									0	0	0
Subsidiary preferred stock dividends									0	0	0
Segment earnings (loss) attributable to PNMR									(27,553)	(1,714)	(10,561)
Total Assets	223,770				220,311				223,770	220,311	112,845
Goodwill	$ 0				$ 0				$ 0	$ 0	$ 0