Accumulated Other Comprehensive Income (Loss) (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Accumulated Other Comprehensive Income (Loss), Net of Tax [Line Items]
Unrealized gain on securities	$ 15,634	$ 16,211
Pension liability adjustment	(82,432)	(83,254)
Mark-to-market for cash-flow hedge transactions	(58)	(1,623)
Accumulated other comprehensive income (loss)	(66,856)	(68,666)
Public Service Company of New Mexico [Member]
Accumulated Other Comprehensive Income (Loss), Net of Tax [Line Items]
Unrealized gain on securities	15,634	16,211
Pension liability adjustment	(82,432)	(82,981)
Mark-to-market for cash-flow hedge transactions	0	(16)
Accumulated other comprehensive income (loss)	(66,798)	(66,786)
Texas-New Mexico Power Company [Member]
Accumulated Other Comprehensive Income (Loss), Net of Tax [Line Items]
Unrealized gain on securities	0	0
Pension liability adjustment	0	(275)
Mark-to-market for cash-flow hedge transactions	(58)	(1,210)
Accumulated other comprehensive income (loss)	$ (58)	$ (1,485)