Income Taxes Schedule of Deferred Tax Assets and Liabilities (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Components of Deferred Tax Assets [Abstract]
Net operating loss	$ 86,985	$ 72,950
Pension	50,515	58,267
Regulatory liabilities related to income taxes	49,413	17,037
Optim Energy	0	46,508
Other	109,875	96,379
Total deferred tax assets	296,788	291,141
Components of Deferred Tax Liabilities [Abstract]
Depreciation and plant related	(697,528)	(579,505)
Investment tax credit	(15,771)	(18,089)
Regulatory assets related to income taxes	(56,312)	(53,287)
Stranded costs	(28,439)	(33,287)
Other	(168,688)	(164,282)
Total deferred tax liabilities	966,738	848,450
Deferred Tax Assets (Liabilities), Net [Abstract]
Net accumulated deferred income tax liabilities	(669,950)	(557,309)
Current accumulated deferred income tax (asset) liability	9,080	(886)
Non-current accumulated deferred income tax liability	(660,870)	(558,195)
Texas-New Mexico Power Company [Member]
Components of Deferred Tax Assets [Abstract]
Regulatory liabilities related to income taxes	5,835	6,259
Other	16,043	16,638
Total deferred tax assets	21,878	22,897
Components of Deferred Tax Liabilities [Abstract]
Depreciation and plant related	(125,270)	(103,456)
Regulatory assets related to income taxes	(10,981)	(11,217)
Stranded costs	(28,439)	(33,287)
Other	(14,113)	(15,182)
Total deferred tax liabilities	178,803	163,142
Deferred Tax Assets (Liabilities), Net [Abstract]
Net accumulated deferred income tax liabilities	(156,925)	(140,245)
Current accumulated deferred income tax (asset) liability	(2,272)	(1,876)
Non-current accumulated deferred income tax liability	(159,197)	(142,121)
Public Service Company of New Mexico [Member]
Components of Deferred Tax Assets [Abstract]
Net operating loss	72,615	66,320
Pension	54,270	61,055
Regulatory liabilities related to income taxes	43,578	10,779
Other	47,263	52,161
Total deferred tax assets	217,726	190,315
Components of Deferred Tax Liabilities [Abstract]
Depreciation and plant related	(570,278)	(476,533)
Investment tax credit	(15,771)	(18,089)
Regulatory assets related to income taxes	(45,331)	(42,070)
Other	(123,098)	(128,152)
Total deferred tax liabilities	754,478	664,844
Deferred Tax Assets (Liabilities), Net [Abstract]
Net accumulated deferred income tax liabilities	(536,752)	(474,529)
Current accumulated deferred income tax (asset) liability	16,562	9,783
Non-current accumulated deferred income tax liability	$ (520,190)	$ (464,746)