Income Taxes Schedule of Components of Income Tax Expense (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Income Taxes [Line Items]
Current federal income tax	$ 1,319	$ (52,184)	$ (81,963)
Current state income tax	(4,208)	(15,528)	(3,770)
Deferred federal income tax	119,280	28,364	112,707
Deferred state income tax	7,462	9,522	4,393
Amortization of accumulated investment tax credits	(2,318)	(2,429)	(2,549)
Income income taxes (benefit)	121,535	(32,255)	28,818
Public Service Company of New Mexico [Member]
Income Taxes [Line Items]
Current federal income tax	(46,364)	(77,691)	(64,342)
Current state income tax	(6,776)	438	(13,621)
Deferred federal income tax	78,673	109,170	77,264
Deferred state income tax	14,212	6,939	16,974
Amortization of accumulated investment tax credits	(2,318)	(2,429)	(2,549)
Income income taxes (benefit)	37,427	36,427	13,726
Texas-New Mexico Power Company [Member]
Income Taxes [Line Items]
Current federal income tax	(3,578)	3,532	(25,237)
Current state income tax	1,981	1,766	1,584
Deferred federal income tax	15,507	4,775	31,664
Deferred state income tax	(29)	(29)	(26)
Income income taxes (benefit)	$ 13,881	$ 10,044	$ 7,985