XML 78 R59.htm IDEA: XBRL DOCUMENT v3.10.0.1
Commitments and Contingencies - Coal Supply (Details)
 6 Months Ended 12 Months Ended
Jun. 29, 2018
USD ($)
Mar. 17, 2018
T
Feb. 01, 2016
USD ($)
Jun. 30, 2018
USD ($)
Dec. 31, 2017
USD ($)
May 22, 2018
USD ($)
Feb. 01, 2018
Jun. 30, 2017
USD ($)
Feb. 01, 2017
Aug. 01, 2016
payment
Jan. 31, 2016
USD ($)
Public Utilities, Commitments And Contingencies [Line Items]                      
Other current assets       $ 51,818,000 $ 47,358,000            
PNM                      
Public Utilities, Commitments And Contingencies [Line Items]                      
Other current assets       46,369,000 39,904,000            
PNM | Surface                      
Public Utilities, Commitments And Contingencies [Line Items]                      
Regulatory assets       100,000,000              
PNM | Loss on long-term purchase commitment | Surface                      
Public Utilities, Commitments And Contingencies [Line Items]                      
Loss contingency accrual       40,500,000 41,400,000            
Increase (decrease) for interim storage costs liability         35,000,000            
Final reclamation, capped amount to be collected       100,000,000.0              
PNM | Loss on long-term purchase commitment | Underground                      
Public Utilities, Commitments And Contingencies [Line Items]                      
Loss contingency accrual       15,400,000 14,700,000            
Increase (decrease) for interim storage costs liability         5,000,000            
PNM | Loss on long-term purchase commitment | San Juan Generating Station | Surface                      
Public Utilities, Commitments And Contingencies [Line Items]                      
Estimate of possible loss       98,500,000              
PNM | Loss on long-term purchase commitment | San Juan Generating Station | Underground                      
Public Utilities, Commitments And Contingencies [Line Items]                      
Estimate of possible loss       127,100,000              
Coal supply | PNM | San Juan Generating Station                      
Public Utilities, Commitments And Contingencies [Line Items]                      
Other current assets       $ 26,300,000 26,300,000            
Reduction in coal obligation | T   113,000.000                  
Estimated increase in coal cost       6.90%       51.00%      
Coal supply | NM Capital | San Juan Generating Station                      
Public Utilities, Commitments And Contingencies [Line Items]                      
Payments to fund long-term loans to unaffiliated third party     $ 125,000,000.0                
Loan agreement among several entities     125,000,000.0                
Interest rate             12.25%   9.25%    
Requirement to post reclamation bonds       $ 118,700,000              
Cash used to support bank letter or credit arrangement       30,300,000             $ 30,300,000
Coal supply | NM Capital | San Juan Coal Company, Westmoreland                      
Public Utilities, Commitments And Contingencies [Line Items]                      
Payments to fund long-term loans to unaffiliated third party     125,000,000.0                
Prepayment penalty       0              
Repayment of line of credit           $ 50,100,000          
BTMU Term Loan Agreement | NM Capital                      
Public Utilities, Commitments And Contingencies [Line Items]                      
Long-term debt     125,000,000.0                
Repayment of line of credit     $ 125,000,000     $ 43,000,000          
Mine Reclamation Trust | PNM                      
Public Utilities, Commitments And Contingencies [Line Items]                      
Required contribution to Reclamation Trust, current fiscal year       7,200,000              
Reclamation trust funding, year 2       8,700,000              
Reclamation trust funding, year 3       9,200,000              
San Juan Generating Station | Loss on long-term purchase commitment | PNM                      
Public Utilities, Commitments And Contingencies [Line Items]                      
Annual funding post-term reclamation trust         $ 5,800,000            
Four Corners | Mine Reclamation Trust | PNM                      
Public Utilities, Commitments And Contingencies [Line Items]                      
Required contribution to Reclamation Trust, current fiscal year               $ 2,300,000      
Reclamation trust funding, year 2       2,300,000              
Reclamation trust funding, year 3       $ 2,300,000              
Number of annual installment payments | payment                   13  
Four Corners Coal Supply Arbitration | PNM                      
Public Utilities, Commitments And Contingencies [Line Items]                      
Payments for legal settlements $ 4,900,000                    
Four Corners Coal Supply Arbitration, Period March 1, 2018 through June 30, 2018 | PNM                      
Public Utilities, Commitments And Contingencies [Line Items]                      
Payments for legal settlements $ 1,400,000