Segment Information (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended												12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011		Sep. 30, 2011		Jun. 30, 2011		Mar. 31, 2011		Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Segment Reporting Information, Profit (Loss) [Abstract]
Operating revenues	$ 322,758	$ 390,411	$ 323,860	$ 305,374	$ 347,872		$ 549,498		$ 415,586		$ 387,663		$ 1,342,403	$ 1,700,619	$ 1,673,517
Intersegment revenues														0	0
Total revenues														1,700,619	1,673,517
Cost of energy													399,850	692,922	700,727
Gross margin													942,553	1,007,697	972,790
Other operating expenses													504,659	593,351	581,634
Depreciation and amortization													164,173	157,047	151,704
Operating income	36,736	118,150	65,106	53,729	63,935		108,284		32,860		52,220		273,721	257,299	239,452
Interest income													13,072	15,515	18,896
Gain on sale of First Choice													1,012	174,925	0
Equity in net earnings (loss) of Optim Energy															(203,399)
Other income (deductions)													8,075	(10,421)	7,045
Net interest charges													(120,845)	(124,849)	(125,373)
Earnings (Loss) before Income Taxes													175,035	312,469	(63,379)
Income Taxes (Benefit)													54,910	121,535	(32,255)
Net earnings	12,573	61,976	25,099	20,477	115,408	[1]	47,905	[1]	7,669	[1]	19,952	[1]	120,125	190,934	(31,124)
Earnings (loss) from continuing operations															(31,124)
Valencia non-controlling interest													(14,050)	(14,047)	(13,563)
Preferred Stock Dividend Requirements of Subsidiary													(528)	(528)	(528)
Segment earnings (loss) from continuing operations attributable to PNMR (excluding discontinued operations amounts related to sale of PNM Gas)															(45,215)
Net Earnings (Loss) Attributable to PNMR	9,091	57,864	21,512	17,080	111,993		43,662		4,067		16,637		105,547	176,359	(45,215)
Gross property additions													308,909	326,931	281,488
Gross property additions															281,488
Total Assets	5,372,583				5,204,613								5,372,583	5,204,613	5,225,083
Goodwill	278,297				278,297								278,297	278,297	321,310
Additions to utility and non-utility plant included in accounts payable	15,672				33,655								15,672	33,655
PNM [Member]
Segment Reporting Information, Profit (Loss) [Abstract]
Operating revenues													1,092,264	1,057,289	1,017,128
Intersegment revenues														0	0
Total revenues														1,057,289	1,017,128
Cost of energy													353,649	362,237	352,270
Gross margin													738,615	695,052	664,858
Other operating expenses													435,442	438,822	424,455
Depreciation and amortization													97,291	94,787	92,281
Operating income													205,882	161,443	148,122
Interest income													13,243	15,562	18,854
Gain on sale of First Choice													0	0
Equity in net earnings (loss) of Optim Energy															0
Other income (deductions)													13,290	4,309	12,712
Net interest charges													(76,101)	(75,349)	(72,400)
Earnings (Loss) before Income Taxes													156,314	105,965	107,288
Income Taxes (Benefit)													50,713	37,427	36,427
Net earnings													105,601	68,538
Earnings (loss) from continuing operations															70,861
Valencia non-controlling interest													(14,050)	(14,047)	(13,563)
Preferred Stock Dividend Requirements of Subsidiary													(528)	(528)	(528)
Segment earnings (loss) from continuing operations attributable to PNMR (excluding discontinued operations amounts related to sale of PNM Gas)															56,770
Net Earnings (Loss) Attributable to PNMR													91,023	53,963
Gross property additions													196,800	251,345
Gross property additions															226,766
Total Assets	4,163,907				4,095,287								4,163,907	4,095,287	3,875,573
Goodwill	51,632				51,632								51,632	51,632	51,632
Additions to utility and non-utility plant included in accounts payable	7,083				26,815								7,083	26,815
TNMP [Member]
Segment Reporting Information, Profit (Loss) [Abstract]
Operating revenues													250,140	204,045	173,504
Intersegment revenues														33,813	39,084
Total revenues														237,858	212,588
Cost of energy													46,201	41,166	37,064
Gross margin													203,939	196,692	175,524
Other operating expenses													87,079	88,234	77,387
Depreciation and amortization													49,340	44,616	41,726
Operating income													67,520	63,842	56,411
Interest income													1	2	1
Gain on sale of First Choice													0	0
Equity in net earnings (loss) of Optim Energy															0
Other income (deductions)													2,739	1,580	771
Net interest charges													(28,161)	(29,286)	(31,157)
Earnings (Loss) before Income Taxes													42,099	36,138	26,026
Income Taxes (Benefit)													15,352	13,881	10,044
Valencia non-controlling interest													0	0	0
Preferred Stock Dividend Requirements of Subsidiary													0	0	0
Net Earnings (Loss) Attributable to PNMR													26,747	22,257	15,982
Gross property additions													92,973	67,407
Gross property additions															41,018
Total Assets	1,086,229				1,037,445								1,086,229	1,037,445	1,010,957
Goodwill	226,665				226,665								226,665	226,665	226,665
Additions to utility and non-utility plant included in accounts payable	1,987				4,736								1,987	4,736
First Choice [Member]
Segment Reporting Information, Profit (Loss) [Abstract]
Operating revenues														439,450	483,203
Intersegment revenues														0	0
Total revenues														439,450	483,203
Cost of energy														323,331	350,476
Gross margin														116,119	132,727
Other operating expenses														75,966	92,077
Depreciation and amortization														1,098	864
Operating income														39,055	39,786
Interest income														64	18
Gain on sale of First Choice														0
Equity in net earnings (loss) of Optim Energy															0
Other income (deductions)														(650)	(411)
Net interest charges														(581)	(1,268)
Earnings (Loss) before Income Taxes														37,888	38,125
Income Taxes (Benefit)														13,772	14,064
Valencia non-controlling interest														0	0
Preferred Stock Dividend Requirements of Subsidiary														0	0
Net Earnings (Loss) Attributable to PNMR														24,116	24,061
Gross property additions														2,089
Gross property additions															3,046
Total Assets					0									0	218,411
Goodwill					0									0	43,013
Additions to utility and non-utility plant included in accounts payable					0									0
Corporate and Other [Member]
Segment Reporting Information, Profit (Loss) [Abstract]
Operating revenues													(1)	(165)	(318)
Intersegment revenues														(33,813)	(39,084)
Total revenues														(33,978)	(39,402)
Cost of energy													0	(33,812)	(39,083)
Gross margin													(1)	(166)	(319)
Other operating expenses													(17,862)	(9,671)	(12,285)
Depreciation and amortization													17,542	16,546	16,833
Operating income													319	(7,041)	(4,867)
Interest income													(172)	(113)	23
Gain on sale of First Choice													1,012	174,925
Equity in net earnings (loss) of Optim Energy															(203,399)
Other income (deductions)													(7,954)	(15,660)	(6,027)
Net interest charges													(16,583)	(19,633)	(20,548)
Earnings (Loss) before Income Taxes													(23,378)	132,478	(234,818)
Income Taxes (Benefit)													(11,155)	56,455	(92,790)
Valencia non-controlling interest													0	0	0
Preferred Stock Dividend Requirements of Subsidiary													0	0	0
Net Earnings (Loss) Attributable to PNMR													(12,223)	76,023	(142,028)
Gross property additions													19,136	6,090
Gross property additions															10,658
Total Assets	122,447				71,881								122,447	71,881	120,142
Goodwill	0				0								0	0	0
Additions to utility and non-utility plant included in accounts payable	$ 6,602				$ 2,104								$ 6,602	$ 2,104

[1] During the fourth quarter of 2011, PNMR completed the sale of First Choice which resulted in a $174.9 million ($97.0 million after-tax) gain, that positively affected net earnings, net earnings attributable to PNMR, and earnings per share. See Note 3.