Fair Value of Derivative and Other Financial Instruments, Unobservable Input Reconciliation (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2011		Dec. 31, 2010
Fair Value, Assets And Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period	$ (822)		$ 248
Total gains (losses) included in earnings	1,020		(1,646)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases	3,163		70
Settlements	(1,578)	[1]	506	[1]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Sales	(1,783)		0
Balance at end of period	0		(822)
Total gains (losses) included in earnings attributable to the change in unrealized gains or losses relating to assets still held at the end of period	0		(1,087)
Public Service Company of New Mexico [Member]
Fair Value, Assets And Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period	0		(17)
Total gains (losses) included in earnings	0		(128)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases	0		0
Settlements	0	[1]	145	[1]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Sales	0		0
Balance at end of period	0		0
Total gains (losses) included in earnings attributable to the change in unrealized gains or losses relating to assets still held at the end of period	$ 0		$ 0

[1] The above gains and losses (realized and unrealized) for Level 3 fair value measurements included in earnings are reported in cost of energy.