Condensed Consolidated Statements of Changes in Equity (USD $) In Thousands, unless otherwise specified	Total	Common Stock [Member]	AOCI [Member]	Retained Earnings [Member]	Total Company Common Stockholders' Equity [Member]	Non-controlling Interest in Valencia [Member]	Public Service Company of New Mexico [Member]	Public Service Company of New Mexico [Member] Common Stock [Member]	Public Service Company of New Mexico [Member] AOCI [Member]	Public Service Company of New Mexico [Member] Retained Earnings [Member]	Public Service Company of New Mexico [Member] Total Company Common Stockholders' Equity [Member]	Public Service Company of New Mexico [Member] Non-controlling Interest in Valencia [Member]	Texas-New Mexico Power Company [Member]	Texas-New Mexico Power Company [Member] Common Stock [Member]	Texas-New Mexico Power Company [Member] Additional Paid-in Capital [Member]	Texas-New Mexico Power Company [Member] AOCI [Member]	Texas-New Mexico Power Company [Member] Retained Earnings [Member]
Balance at Dec. 31, 2012	$ 1,689,030	$ 1,182,819	$ (81,630)	$ 506,998	$ 1,608,187	$ 80,843	$ 1,334,906	$ 1,061,776	$ (81,414)	$ 273,701	$ 1,254,063	$ 80,843
Balance TNMP at Dec. 31, 2012	1,608,187						1,254,063						463,814	64	390,366	(216)	73,600
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Proceeds from stock option exercise	11,345	11,345	0	0	11,345	0
Awards of common stock	(19,741)	(19,741)	0	0	(19,741)	0
Excess tax (shortfall) from stock-based payment arrangements	(458)	(458)	0	0	(458)	0
Stock based compensation expense	3,198	3,198	0	0	3,198	0
Valencia's transactions with its owner	(8,675)	0	0	0	0	(8,675)	(8,675)	0	0	0	0	(8,675)
Net Earnings	38,304						37,693						12,065	0	0	0	12,065
Net earnings before subsidiary preferred stock dividends	45,345	0	0	38,568	38,568	6,777	44,470	0	0	37,693	37,693	6,777
Subsidiary preferred stock dividends	(264)	0	0	(264)	(264)	0
Total other comprehensive income (loss)	3,036	0	3,036	0	3,036	0	2,970	0	2,970	0	2,970	0	66	0	0	66	0
Dividends declared on preferred stock							(264)	0	0	(264)	(264)	0
Dividends declared on common stock	(13,142)	0	0	(13,142)	(13,142)	0	0						(3,726)	0	0	0	(3,726)
Balance at Jun. 30, 2013	1,709,674	1,177,163	(78,594)	532,160	1,630,729	78,945	1,373,407	1,061,776	(78,444)	311,130	1,294,462	78,945
Balance at Mar. 31, 2013	1,709,674						1,373,407
Balance TNMP at Mar. 31, 2013	1,630,729						1,294,462						472,219	64	390,366	(150)	81,939
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Earnings	27,678						26,124						8,339
Net earnings before subsidiary preferred stock dividends	31,383						29,697
Subsidiary preferred stock dividends	(132)
Total other comprehensive income (loss)	(1,903)						(1,930)						27
Balance at Jun. 30, 2013	$ 1,709,674						$ 1,373,407