Fair Value of Derivative and Other Financial Instruments, Derivative Balance Sheet Information (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Derivatives, Fair Value [Line Items]
Commodity derivative instruments, Current assets	$ 3,713	$ 15,999
Commodity derivative instruments, Deferred charges	0	5,264
Commodity derivative instruments, Current liabilities	(1,632)	(31,407)
Commodity derivative instruments, Long-term liabilities	(2,437)	(12,831)
Public Service Company of New Mexico [Member]
Derivatives, Fair Value [Line Items]
Commodity derivative instruments, Current assets	3,713	1,443
Commodity derivative instruments, Current liabilities	(1,632)	(3,110)
Commodity derivative instruments, Long-term liabilities	(2,437)	(2,009)
Commodity Contract [Member] | Economic hedges [Member]
Derivatives, Fair Value [Line Items]
Commodity derivative instruments, Current assets	3,713	15,999
Commodity derivative instruments, Deferred charges	0	5,264
Commodity derivative instruments, Assets	3,713	21,263
Commodity derivative instruments, Current liabilities	(1,632)	(31,407)
Commodity derivative instruments, Long-term liabilities	(2,437)	(12,831)
Commodity derivative instruments, Liabilities	(4,069)	(44,238)
Commodity derivative instruments, Net	(356)	(22,975)
Commodity Contract [Member] | Economic hedges [Member] | Public Service Company of New Mexico [Member]
Derivatives, Fair Value [Line Items]
Commodity derivative instruments, Current assets	3,713	1,443
Commodity derivative instruments, Current liabilities	(1,632)	(3,110)
Commodity derivative instruments, Long-term liabilities	(2,437)	(2,009)
Commodity derivative instruments, Liabilities	(4,069)	(5,119)
Commodity derivative instruments, Net	(356)	(3,676)
Commodity Contract [Member] | Fuel and purchased power adjustment clause [Member] | Economic hedges [Member] | Public Service Company of New Mexico [Member]
Derivatives, Fair Value [Line Items]
Commodity derivative instruments, Current assets	500	600
Commodity derivative instruments, Current liabilities	$ (500)