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Income Taxes - Carryforwards (Details) - USD ($)
 12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Operating Loss Carryforwards [Line Items]          
New Mexico corporate tax rate being phased in         7.60%
New Mexico Corporate tax rate, effective by 2018       5.90%  
Regulatory liability $ (7,132,000) $ (1,903,000) $ (5,106,000)    
Increase/Decrease in Income Tax expense due to tax rate change (712,000) 674,000 71,000    
Income Taxes, Impairment of Carryforwards [Abstract]          
State tax credit carryforwards 0 3,092,000 894,000    
State net operating loss carryforwards (311,000) 5,278,000 3,129,000    
Charitable contribution carryforwards 0 2,042,000      
Income Taxes, Reserve Balances [Abstract]          
State tax credit carryforwards 3,986,000 6,378,000      
State net operating loss carryforwards 361,000 361,000      
Charitable contribution carryforwards 659,000 659,000      
Liability (refund) adjustment from settlement with taxing authority     (2,000,000)    
Income tax expense (benefit) 63,278,000 15,075,000 69,738,000    
Corporate and Other [Member]          
Income Taxes, Reserve Balances [Abstract]          
Income tax expense (benefit) (1,480,000) 3,708,000 (5,418,000)    
Internal Revenue Service (IRS) [Member]          
Operating Loss Carryforwards [Line Items]          
Federal net operating loss carryforwards 420,100,000        
Federal tax credit carryforwards that expire beginning in 2023 78,700,000        
Income Taxes, Reserve Balances [Abstract]          
Income tax expense (benefit)     (200,000)    
Internal Revenue Service (IRS) [Member] | Corporate and Other [Member]          
Income Taxes, Reserve Balances [Abstract]          
Income tax expense (benefit)     (1,300,000)    
Public Service Company of New Mexico [Member]          
Operating Loss Carryforwards [Line Items]          
Regulatory liability (7,132,000) (1,903,000) (5,106,000)    
Increase/Decrease in Income Tax expense due to tax rate change (804,000) 470,000 312,000    
Income Taxes, Impairment of Carryforwards [Abstract]          
State tax credit carryforwards 0 0 0    
State net operating loss carryforwards (213,000) 3,619,000 2,145,000    
Charitable contribution carryforwards 0 0      
Income Taxes, Reserve Balances [Abstract]          
State tax credit carryforwards 0 0      
State net operating loss carryforwards 248,000 248,000      
Charitable contribution carryforwards 0 0      
Income tax expense (benefit) 40,922,000 (12,758,000) 52,633,000    
Public Service Company of New Mexico [Member] | Internal Revenue Service (IRS) [Member]          
Income Taxes, Reserve Balances [Abstract]          
Income tax expense (benefit)     1,100,000    
Texas-New Mexico Power Company [Member]          
Operating Loss Carryforwards [Line Items]          
Regulatory liability 0 0 0    
Increase/Decrease in Income Tax expense due to tax rate change 0 0 0    
Income Taxes, Impairment of Carryforwards [Abstract]          
State tax credit carryforwards 0 0 0    
State net operating loss carryforwards 0 0 0    
Charitable contribution carryforwards 0 0      
Income Taxes, Reserve Balances [Abstract]          
State tax credit carryforwards 0 0      
State net operating loss carryforwards 0 0      
Charitable contribution carryforwards 0 0      
Income tax expense (benefit) 23,836,000 $ 24,125,000 22,523,000    
Texas-New Mexico Power Company [Member] | Internal Revenue Service (IRS) [Member]          
Income Taxes, Reserve Balances [Abstract]          
Income tax expense (benefit)     $ 0    
2015 Electric Rate Case [Member] | Public Service Company of New Mexico [Member]          
Income Taxes, Reserve Balances [Abstract]          
Approval to recover impairment of net operating loss carryforward $ (2,100,000)        
Recovery period of regulatory asset   2 years