Income Taxes Schedule of Deferred Income Tax Components (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Income Taxes [Line Items]
Net change in deferred income tax liability per above table	$ 46,095
Change in tax effects of income tax related regulatory assets and liabilities	942
Tax effect of mark-to-market adjustments	(570)
Tax effect of excess pension liability	10,085
Adjustment for uncertain income tax positions	(381)
Other	72
Deferred income taxes	56,243	124,424	35,674
Public Service Company of New Mexico [Member]
Income Taxes [Line Items]
Net change in deferred income tax liability per above table	54,818
Change in tax effects of income tax related regulatory assets and liabilities	1,054
Tax effect of mark-to-market adjustments	(506)
Tax effect of excess pension liability	10,085
Adjustment for uncertain income tax positions	(370)
Other	398
Deferred income taxes	65,479	90,567	113,680
Texas-New Mexico Power Company [Member]
Income Taxes [Line Items]
Net change in deferred income tax liability per above table	5,654
Change in tax effects of income tax related regulatory assets and liabilities	(112)
Adjustment for uncertain income tax positions	(905)
Other	(259)
Deferred income taxes	$ 4,378	$ 15,478	$ 4,962