Income Taxes Schedule of Effective Income Tax Rate Reconciliation (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Income Taxes [Line Items]
Federal income tax at statutory rates	$ 109,364	$ (22,183)	$ 33,163
Goodwill, Impairment Loss	15,055
Investment tax credits	(2,318)	(2,429)	(2,549)
Flow-through of depreciation items	3,659	3,995	3,777
Earnings attributable to non-controlling interest	(4,917)	(4,747)	(4,162)
State income tax	3,395	(6,312)	344
Other	(2,703)	(579)	(1,755)
Income income taxes (benefit)	121,535	(32,255)	28,818
Effective tax rate	38.90%	50.89%	30.41%
Public Service Company of New Mexico [Member]
Income Taxes [Line Items]
Federal income tax at statutory rates	37,088	37,551	15,969
Investment tax credits	(2,318)	(2,429)	(2,549)
Flow-through of depreciation items	3,656	3,994	3,776
Earnings attributable to non-controlling interest	(4,917)	(4,747)	(4,162)
State income tax	4,797	4,747	1,933
Other	(879)	(2,689)	(1,241)
Income income taxes (benefit)	37,427	36,427	13,726
Effective tax rate	35.32%	34.00%	30.00%
Texas-New Mexico Power Company [Member]
Income Taxes [Line Items]
Federal income tax at statutory rates	12,648	9,109	7,053
State income tax	1,288	1,148	1,032
Other	(55)	(213)	(100)
Income income taxes (benefit)	13,881	10,044	7,985
Effective tax rate	38.41%	38.59%	39.63%
First Choice [Member]
Income Taxes [Line Items]
Goodwill, Impairment Loss		$ 0	$ 0