Quarterly Operating Results (Unaudited) (Details) - USD ($) $ / shares in Units, $ 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]
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
Operating income	22,936	142,484	85,105	55,960	63,584	108,071	64,822	41,508	306,485	277,985	124,350
Net earnings (loss)	(50,585)	78,327	41,231	26,446	28,423	58,556	30,952	13,965	95,419	131,896	31,078
Net Earnings Attributable to PNMR	$ (54,282)	$ 73,739	$ 37,555	$ 22,862	$ 24,809	$ 54,418	$ 27,076	$ 10,546	$ 79,874	$ 116,849	$ 15,640
Net Earnings Attributable to PNMR per Common Share:
Basic (in dollars per share)	$ (0.68)	$ 0.92	$ 0.47	$ 0.29	$ 0.32	$ 0.68	$ 0.34	$ 0.13	$ 1.00	$ 1.47	$ 0.20
Diluted (in dollars per share)	$ (0.68)	$ 0.92	$ 0.47	$ 0.29	$ 0.31	$ 0.68	$ 0.34	$ 0.13	$ 1.00	$ 1.46	$ 0.20
Federal income tax rate change									$ 57,461	$ 0	$ 0
Public Service Company of New Mexico
Segment Reporting Information [Line Items]
Operating revenues	$ 249,321	$ 327,254	$ 276,097	$ 251,558	$ 255,685	$ 311,276	$ 233,346	$ 235,606	1,104,230	1,035,913	1,131,195
Operating income	1,778	113,252	59,164	38,331	42,976	80,057	41,760	23,297	212,525	188,090	33,380
Net earnings (loss)	(28,456)	65,283	30,476	20,110	19,594	44,990	19,793	7,561	87,413	91,938	(324)
Net Earnings Attributable to PNMR	(32,021)	60,827	26,932	16,658	16,112	40,984	16,049	4,274	72,396	77,419	(15,234)
Net Earnings Attributable to PNMR per Common Share:
Federal income tax rate change									29,606	0	0
Texas-New Mexico Power Company
Segment Reporting Information [Line Items]
Operating revenues									340,773	327,038	307,887
Operating revenues	83,284	92,646	86,223	78,620	80,540	89,098	82,045	75,355
Operating income	19,879	29,474	26,286	17,965	21,353	28,359	23,375	18,554	93,604	91,641	90,033
Net Earnings Attributable to PNMR	1,024	$ 14,727	$ 12,204	$ 7,604	$ 9,855	$ 13,853	$ 10,508	$ 7,456	35,559	41,672	41,963
Net Earnings Attributable to PNMR per Common Share:
Federal income tax rate change									7,865	$ 0	$ 0
NMPRC
Net Earnings Attributable to PNMR per Common Share:
Pre-tax regulatory disallowance	$ 27,900								$ 27,900