Stockholders' Equity (Details) (USD $)	0 Months Ended			12 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, 2012 Public Service Company of New Mexico [Member]	Dec. 31, 2011 Public Service Company of New Mexico [Member]	Dec. 31, 2010 Public Service Company of New Mexico [Member]	Dec. 31, 2012 Texas-New Mexico Power Company [Member]	Jan. 31, 2011 Affiliated Entity [Member] Public Service Company of New Mexico [Member]	Dec. 31, 2012 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, 2012 Affiliated Entity [Member] Texas-New Mexico Power Company [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, 2012 Line of Credit [Member] Texas-New Mexico Power Company [Member]
Class of Stock [Line Items]
Equity contribution from parent				$ 0	$ 43,000,000	$ 0
Cash dividends paid to parent company by consolidated subsidiaries								39,100,000	34,400,000	8,200,000	28,000,000	26,000,000	13,700,000	13,100,000
Ratio of debt to capital, maximum (as a percent)	65.00%														65.00%
Amount available for dividend distribution without prior approval from regulators or financial counterparties				$ 208,000,000			$ 181,000,000
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