Regulatory Assets and Liabilities (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Regulatory Assets
Regulatory Assets, Current	$ 44,993	$ 36,292
Regulatory Assets, Noncurrent	482,155	502,467
Regulatory Liabilities
Regulatory liabilities, Noncurrent	(418,098)	(342,465)
Public Service Company of New Mexico [Member]
Regulatory Assets
Regulatory Assets, Current	44,480	35,835
Regulatory Assets, Noncurrent	352,387	357,944
Regulatory Assets	396,867	393,779
Regulatory Liabilities
Regulatory liabilities, Noncurrent	(373,703)	(299,763)
Texas-New Mexico Power Company [Member]
Regulatory Assets
Regulatory Assets, Current	513	457
Regulatory Assets, Noncurrent	129,768	144,522
Regulatory Assets	130,281	144,979
Regulatory Liabilities
Regulatory liabilities, Noncurrent	(44,395)	(42,702)
Cost of removal [Member] | Public Service Company of New Mexico [Member]
Regulatory Liabilities
Regulatory liabilities, Noncurrent	(250,778)	(239,928)
Cost of removal [Member] | Texas-New Mexico Power Company [Member]
Regulatory Liabilities
Regulatory liabilities, Noncurrent	(32,786)	(33,496)
Deferred income taxes Member] | Public Service Company of New Mexico [Member]
Regulatory Liabilities
Regulatory liabilities, Noncurrent	(45,323)	(12,575)
Deferred income taxes Member] | Texas-New Mexico Power Company [Member]
Regulatory Liabilities
Regulatory liabilities, Noncurrent	(5,843)	(6,482)
Asset retirement obligations [Member] | Public Service Company of New Mexico [Member]
Regulatory Liabilities
Regulatory liabilities, Noncurrent	(39,979)	(40,369)
Renewable energy tax benefits [Member] | Public Service Company of New Mexico [Member]
Regulatory Liabilities
Regulatory liabilities, Noncurrent	(27,958)	0
Other [Member] | Public Service Company of New Mexico [Member]
Regulatory Liabilities
Regulatory liabilities, Noncurrent	(9,665)	(6,891)
Other [Member] | Texas-New Mexico Power Company [Member]
Regulatory Liabilities
Regulatory liabilities, Noncurrent	(5,766)	(2,724)
Fuel and purchased power adjustment clause [Member]
Regulatory Assets
Regulatory Assets, Current	30,500
Fuel and purchased power adjustment clause [Member] | Public Service Company of New Mexico [Member]
Regulatory Assets
Regulatory Assets, Current	41,254	35,835
Other [Member] | Public Service Company of New Mexico [Member]
Regulatory Assets
Regulatory Assets, Current	3,226	0
Stranded costs [Member] | Texas-New Mexico Power Company [Member]
Regulatory Assets
Regulatory Assets, Noncurrent	81,256	95,105
Coal mine reclamation costs [Member] | Public Service Company of New Mexico [Member]
Regulatory Assets
Regulatory Assets, Noncurrent	51,985	57,906
Deferred income taxes Member] | Public Service Company of New Mexico [Member]
Regulatory Assets
Regulatory Assets, Noncurrent	51,436	48,226
Deferred income taxes Member] | Texas-New Mexico Power Company [Member]
Regulatory Assets
Regulatory Assets, Noncurrent	11,491	11,803
Loss on reacquired debt [Member] | Public Service Company of New Mexico [Member]
Regulatory Assets
Regulatory Assets, Noncurrent	31,276	34,572
Loss on reacquired debt [Member] | Texas-New Mexico Power Company [Member]
Regulatory Assets
Regulatory Assets, Noncurrent	2,852	0
Pension and OPEB [Member] | Public Service Company of New Mexico [Member]
Regulatory Assets
Regulatory Assets, Noncurrent	208,033	208,620
Pension and OPEB [Member] | Texas-New Mexico Power Company [Member]
Regulatory Assets
Regulatory Assets, Noncurrent	18,818	20,613
Renewable energy tax costs [Member] | Public Service Company of New Mexico [Member]
Regulatory Assets
Regulatory Assets, Noncurrent	9,550	1,896
Hurricane recovery costs [Member] | Texas-New Mexico Power Company [Member]
Regulatory Assets
Regulatory Assets, Noncurrent	9,210	13,683
Other [Member] | Public Service Company of New Mexico [Member]
Regulatory Assets
Regulatory Assets, Noncurrent	107	6,724
Other [Member] | Texas-New Mexico Power Company [Member]
Regulatory Assets
Regulatory Assets, Noncurrent	$ 6,141	$ 3,318