Condensed Consolidated Statement of Changes in Equity - USD ($) $ in Thousands	Total	Total PNMR Common Stockholders’ Equity	Common Stock	AOCI	Retained Earnings	Non- controlling Interest in Valencia	PNM	PNM Total PNMR Common Stockholders’ Equity	PNM Common Stock	PNM AOCI	PNM Retained Earnings	PNM Non- controlling Interest in Valencia	Texas-New Mexico Power Company	Texas-New Mexico Power Company Common Stock	Texas-New Mexico Power Company Paid-in Capital	Texas-New Mexico Power Company Retained Earnings
Beginning balance at Dec. 31, 2016				$ (92,451)						$ (92,428)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net earnings before subsidiary preferred stock dividends	$ 67,677						$ 50,587
Net earnings							43,591						$ 19,808
Total other comprehensive income	6,856						6,834
Subsidiary preferred stock dividends	(264)
Dividends declared on common stock													(17,500)
Ending balance at Jun. 30, 2017	(85,595)									(85,594)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative effect adjustment (Note 7)				(11,208)	$ 11,208					(11,208)	$ 11,208
Balance, as adjusted	1,761,448	$ 1,695,253	$ 1,157,665	(107,148)	644,736	$ 66,195	1,488,369	$ 1,422,174	$ 1,264,918	(108,301)	265,557	$ 66,195
Beginning balance at Dec. 31, 2017	1,761,448	1,695,253	1,157,665	(95,940)	633,528	66,195	1,488,369	1,422,174	1,264,918	(97,093)	254,349	66,195
Beginning balance TNMP at Dec. 31, 2017	1,695,253						1,422,174						634,405	$ 64	$ 504,166	$ 130,175
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net earnings before subsidiary preferred stock dividends	61,248	53,462			53,462	7,786	42,296	34,510			34,510	7,786
Net earnings							34,510						24,779			24,779
Total other comprehensive income	3,391	3,391		3,391			1,592	1,592		1,592
Subsidiary preferred stock dividends	(264)	(264)			(264)
Dividends declared on preferred stock							(264)	(264)			(264)
Dividends declared on common stock	(21,108)	(21,108)			(21,108)								(10,436)			(10,436)
Proceeds from stock option exercise	924	924	924
Awards of common stock	(12,268)	(12,268)	(12,268)
Stock based compensation expense	3,325	3,325	3,325
Valencia’s transactions with its owner	(8,381)					(8,381)	(8,381)					(8,381)
Ending balance at Jun. 30, 2018	1,788,315	$ 1,722,715	$ 1,149,646	$ (103,757)	$ 676,826	$ 65,600	1,523,612	$ 1,458,012	$ 1,264,918	$ (106,709)	$ 299,803	$ 65,600
Ending balance TNMP at Jun. 30, 2018	$ 1,722,715						$ 1,458,012						$ 648,748	$ 64	$ 504,166	$ 144,518