XML 79 R59.htm IDEA: XBRL DOCUMENT v3.10.0.1
Commitments and Contingencies - Coal Supply (Details)
 3 Months Ended 9 Months Ended 12 Months Ended
Oct. 05, 2018
T
Jun. 29, 2018
USD ($)
Feb. 01, 2016
USD ($)
Dec. 31, 2015
USD ($)
Sep. 30, 2018
USD ($)
Sep. 30, 2017
USD ($)
Sep. 30, 2018
USD ($)
Sep. 30, 2017
USD ($)
Dec. 31, 2017
USD ($)
May 22, 2018
USD ($)
Feb. 01, 2018
Jun. 30, 2017
USD ($)
Feb. 01, 2017
Sep. 30, 2016
USD ($)
Aug. 01, 2016
payment
Jan. 31, 2016
USD ($)
Public Utilities, Commitments And Contingencies [Line Items]                                
Other current assets         $ 53,068,000   $ 53,068,000   $ 47,358,000              
Regulatory disallowances and restructuring costs         (1,645,000) $ 0 149,000 $ 0                
PNM                                
Public Utilities, Commitments And Contingencies [Line Items]                                
Other current assets         46,467,000   46,467,000   39,904,000              
Regulatory disallowances and restructuring costs         (1,645,000) $ 0 149,000 $ 0                
PNM | Surface                                
Public Utilities, Commitments And Contingencies [Line Items]                                
Regulatory assets         100,000,000   100,000,000                  
PNM | Loss on long-term purchase commitment | Surface                                
Public Utilities, Commitments And Contingencies [Line Items]                                
Increase (decrease) for interim storage costs liability             30,000,000                  
Loss contingency accrual         39,500,000   39,500,000   41,400,000              
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]                                
Increase (decrease) for interim storage costs liability             10,000,000                  
Loss contingency accrual         14,300,000   14,300,000   14,700,000              
PNM | Loss on long-term purchase commitment | San Juan Generating Station | Surface                                
Public Utilities, Commitments And Contingencies [Line Items]                                
Regulatory disallowances and restructuring costs       $ 16,500,000                        
Estimate of possible loss         87,500,000   87,500,000                  
PNM | Loss on long-term purchase commitment | San Juan Generating Station | Underground                                
Public Utilities, Commitments And Contingencies [Line Items]                                
Estimate of possible loss         $ 101,200,000   $ 101,200,000                  
Coal supply | PNM | San Juan Generating Station                                
Public Utilities, Commitments And Contingencies [Line Items]                                
Other current assets                 26,300,000              
Estimated increase in coal cost         6.90%   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   $ 118,700,000                  
Cash used to support bank letter or credit arrangement         30,300,000   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   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     $ 125,000,000.0             $ 43,000,000            
Increase in coal mine decommissioning liability | PNM | San Juan Generating Station                                
Public Utilities, Commitments And Contingencies [Line Items]                                
Estimated underpaid surface mining royalties under proposed rate change                           $ 4,500,000    
Increase in coal mine decommissioning liability | PNM | Loss on long-term purchase commitment                                
Public Utilities, Commitments And Contingencies [Line Items]                                
Estimated underpaid surface mining royalties under proposed rate change         2,500,000   2,500,000                  
Mine Reclamation Trust | PNM                                
Public Utilities, Commitments And Contingencies [Line Items]                                
Required contribution to Reclamation Trust, current fiscal year         6,400,000   6,400,000                  
Reclamation trust funding, year 2         8,700,000   8,700,000                  
Reclamation trust funding, year 3         9,200,000   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   2,300,000                  
Reclamation trust funding, year 3         $ 2,300,000   $ 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                            
Subsequent event | Coal supply | PNM | San Juan Generating Station                                
Public Utilities, Commitments And Contingencies [Line Items]                                
Reduction in coal obligation | T 111,668                              
Continuous highwall mining | San Juan Generating Station                                
Public Utilities, Commitments And Contingencies [Line Items]                                
PNM's share estimated underpaid surface mining royalties under proposed rate change         46.30%   46.30%                  
Estimated underpaid surface mining royalties under proposed rate change         $ 5,000,000   $ 5,000,000