Stockholders' Equity (Details) (USD $)	0 Months Ended			12 Months Ended					0 Months Ended	1 Months Ended	12 Months Ended
	Oct. 31, 2011	Sep. 23, 2011	Sep. 23, 2011 Series A convertible preferred stock [Member]	Dec. 31, 2011 Public Service Company of New Mexico [Member]	Dec. 31, 2010 Public Service Company of New Mexico [Member]	Dec. 31, 2009 Public Service Company of New Mexico [Member]	Dec. 31, 2009 Texas-New Mexico Power Company [Member]	Dec. 31, 2011 Texas-New Mexico Power Company [Member]	Feb. 05, 2009 Affiliated Entity [Member] Public Service Company of New Mexico [Member]	Jan. 31, 2011 Affiliated Entity [Member] Public Service Company of New Mexico [Member]	Dec. 31, 2011 Affiliated Entity [Member] Public Service Company of New Mexico [Member]	Dec. 31, 2010 Affiliated Entity [Member] Public Service Company of New Mexico [Member]	Dec. 31, 2009 Affiliated Entity [Member] Public Service Company of New Mexico [Member]	Dec. 31, 2011 Affiliated Entity [Member] Texas-New Mexico Power Company [Member]	Dec. 31, 2010 Affiliated Entity [Member] Texas-New Mexico Power Company [Member]	Dec. 31, 2009 Affiliated Entity [Member] Texas-New Mexico Power Company [Member]	Dec. 31, 2011 Line of Credit [Member]	Dec. 31, 2011 Line of Credit [Member] Public Service Company of New Mexico [Member]	Dec. 31, 2011 Line of Credit [Member] Texas-New Mexico Power Company [Member]
Class of Stock [Line Items]
Proceeds from Contributions from Parent				$ (43,000,000)	$ 0	$ (86,253,000)	$ 25,206,000
Cash dividends paid to parent company by consolidated subsidiaries									220,000,000	39,100,000	8,200,000	28,000,000	79,700,000	13,700,000	13,100,000	9,300,000
Ratio of debt to capital, maximum (as a percent)	65.00%																65.00%	65.00%	65.00%
Amount available for dividend distribution without prior approval from regulators or financial counterparties				$ 204,000,000				$ 192,000,000
Agreement to purchase all outstanding shares related to Series A convertible preferred stock (in shares)			477,800
Convertible Preferred Stock, Shares Issued upon Conversion (in shares)		4,778,000	10
Preferred stock, dividend rate (as a percent)				4.58%
Preferred stock, redemption percent (as a percent)				102.00%
Preferred Stock, Shares Outstanding		477,800		115,293	115,293
Preferred stock, cumulative shares authorized (in shares)				10,000,000	10,000,000			1,000,000