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Pension and Other Postretirement Benefit Plans (Other Postretirement Benefits) (Details) (USD $)
In Thousands, unless otherwise specified
12 Months Ended
Dec. 31, 2011
Dec. 31, 2010
Dec. 31, 2009
Defined Contribution Pension and Other Postretirement Plans Disclosure [Abstract]      
Maximum annual contribution per employee (as a percent) 75.00%    
Employer matching contribution (as a percent) 6.00%    
Minimum [Member]
     
Defined Contribution Pension and Other Postretirement Plans Disclosure [Abstract]      
Non-matching contribution of eligible compensation based on eligible employee's age (as a percent) 3.00%    
Maximum [Member]
     
Defined Contribution Pension and Other Postretirement Plans Disclosure [Abstract]      
Non-matching contribution of eligible compensation based on eligible employee's age (as a percent) 10.00%    
401 (k) plan [Member]
     
Defined Contribution Pension and Other Postretirement Plans Disclosure [Abstract]      
Expenses recognized $ 17,000 $ 17,199 $ 16,743
Public Service Company of New Mexico [Member] | 401 (k) plan [Member]
     
Defined Contribution Pension and Other Postretirement Plans Disclosure [Abstract]      
Expenses recognized 12,541 12,788 11,698
Texas-New Mexico Power Company [Member] | 401 (k) plan [Member]
     
Defined Contribution Pension and Other Postretirement Plans Disclosure [Abstract]      
Expenses recognized 3,723 3,496 3,323
Non-qualified plan [Member]
     
Defined Contribution Pension and Other Postretirement Plans Disclosure [Abstract]      
Compensation expense 1,931 2,500 2,073
Non-qualified plan [Member] | Public Service Company of New Mexico [Member]
     
Defined Contribution Pension and Other Postretirement Plans Disclosure [Abstract]      
Compensation expense 1,407 1,871 1,299
Non-qualified plan [Member] | Texas-New Mexico Power Company [Member]
     
Defined Contribution Pension and Other Postretirement Plans Disclosure [Abstract]      
Compensation expense $ 431 $ 478 $ 405