Pension and Other Postretirement Benefit Plans APBO, PBO, Fair Value of Plan Assets, and Funded Status of the Plans (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at end of year	$ 506,605	$ 453,986
Non-current liability	224,766	270,172
Public Service Company of New Mexico [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Non-current liability	213,688	253,948
Public Service Company of New Mexico [Member] | Pension Plan [Member]
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit Obligation at beginning of year	593,457	545,747
Service cost	0	0	0
Interest cost	32,804	34,073	34,439
Actuarial (gain) loss	1,197	51,379
Benefits paid	(38,584)	(37,742)
Benefit Obligation at end of year	588,874	593,457	545,747
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at beginning of year	392,788	360,854
Actual return on plan assets	31,671	51,725
Employer contributions	41,511	17,951
Benefits paid	(38,584)	(37,742)
Fair value of plan assets at end of year	427,386	392,788	360,854
Funded status - asset (liability)	(161,488)	(200,669)
Public Service Company of New Mexico [Member] | Other Postretirement Benefits [Member]
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit Obligation at beginning of year	99,486	122,417
Service cost	259	419	417
Interest cost	5,378	7,650	7,388
Participants contributions	2,206	1,732
Actuarial (gain) loss	712	(17,952)
Benefits paid	(10,315)	(9,331)
Plan amendments	(1,505)	(5,449)
Benefit Obligation at end of year	96,221	99,486	122,417
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at beginning of year	61,749	57,126
Actual return on plan assets	2,263	9,771
Employer contributions	2,873	2,451
Participants contributions	2,206	1,732
Benefits paid	(10,315)	(9,331)
Fair value of plan assets at end of year	58,776	61,749	57,126
Funded status - asset (liability)	(37,445)	(37,737)
Public Service Company of New Mexico [Member] | Executive Retirement Program [Member]
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit Obligation at beginning of year	17,020	17,004
Service cost	0	0	59
Interest cost	930	1,054
Interest cost	930	1,053	1,135
Actuarial (gain) loss	(252)	473
Benefits paid	(1,507)	(1,511)
Benefit Obligation at end of year	16,191	17,020	17,004
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Benefits paid	(1,507)	(1,511)
Less current liability	1,436	1,478
Non-current liability	14,755	15,542
Texas-New Mexico Power Company [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Non-current liability	11,078	16,224
Texas-New Mexico Power Company [Member] | Pension Plan [Member]
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit Obligation at beginning of year	72,260	68,636
Service cost	0	0	0
Interest cost	3,800	4,126	4,396
Actuarial (gain) loss	(2,793)	5,113
Benefits paid	(6,033)	(5,615)
Benefit Obligation at end of year	67,234	72,260	68,636
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at beginning of year	60,387	57,744
Actual return on plan assets	4,447	8,013
Employer contributions	1,151	245
Benefits paid	(6,033)	(5,615)
Fair value of plan assets at end of year	59,952	60,387	57,744
Funded status - asset (liability)	(7,282)	(11,873)
Texas-New Mexico Power Company [Member] | Other Postretirement Benefits [Member]
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit Obligation at beginning of year	12,152	11,554
Service cost	306	289	260
Interest cost	654	711	733
Participants contributions	281	257
Actuarial (gain) loss	(862)	(116)
Benefits paid	(1,187)	(543)
Plan amendments	0	0
Benefit Obligation at end of year	11,344	12,152	11,554
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at beginning of year	8,596	7,093
Actual return on plan assets	262	1,214
Employer contributions	351	575
Participants contributions	281	257
Benefits paid	(1,187)	(543)
Fair value of plan assets at end of year	8,303	8,596	7,093
Funded status - asset (liability)	(3,041)	(3,556)
Texas-New Mexico Power Company [Member] | Executive Retirement Program [Member]
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit Obligation at beginning of year	884	867
Service cost	0	0	0
Interest cost	46	52
Interest cost	46	52	76
Actuarial (gain) loss	8	59
Benefits paid	(94)	(94)
Benefit Obligation at end of year	844	884	867
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Benefits paid	(94)	(94)
Less current liability	89	89
Non-current liability	$ 755	$ 795