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Commitment, Contingencies And Guarentees (Tables)
 12 Months Ended
Dec. 31, 2020
Long-term Purchase Commitment [Line Items]  
Unrecorded Unconditional Purchase Obligations Disclosure
The following is a schedule of unconditional purchase obligations required under the power purchase, transmission services and natural gas transportation and storage agreements (in thousands):
Power purchase and transmission services agreements (a)
Natural gas transportation and storage agreements
2021$24,452 $116,563 
2022$11,678 $121,819 
2023$11,678 $100,282 
2024$2,738 $67,089 
2025$— $50,709 
Thereafter$— $167,100 
_____________
(a)    This schedule does not reflect renewable energy PPA obligations since these agreements vary based on weather conditions.
Schedule of Unit Contingent Capacity The unit-contingent capacity amounts from Wygen III and Neil Simpson II are as follows:
Contract YearsTotal Contract CapacityContingent Capacity Amounts on Wygen IIIContingent Capacity Amounts on Neil Simpson II
2020-202215 MW7 MW8 MW
2022-202315 MW8 MW7 MW
2023-202810 MW5 MW5 MW
Schedule of Guarantor Obligations To the extent liabilities are incurred as a result of activities covered by the surety bonds, such liabilities are included in our Consolidated Balance Sheets.
We had the following guarantees in place as of (in thousands):
Maximum Exposure at
Nature of GuaranteeDecember 31, 2020Expiration
Indemnification for subsidiary reclamation/surety bonds$53,769 Ongoing
Transmission Service Agreement  
Long-term Purchase Commitment [Line Items]  
Long-term Purchase Commitment
Through our subsidiaries, we have the following significant long-term power purchase contracts and transmission services agreement (TSA) with non-affiliated third-parties:

SubsidiaryContract TypeCounterpartyFuel TypeQuantity (MW)Expiration Date
Colorado Electric (a)
PPAPRPAWind60May 31, 2030
Colorado ElectricPPAPRPACoal25June 30, 2024
South Dakota ElectricPPAPacifiCorpCoal50December 31, 2023
South Dakota Electric (b)
TSAPacifiCorpN/A50December 31, 2023
South Dakota ElectricPPAPRPAWind12September 30, 2029
South Dakota ElectricPPAFall River Solar, LLCSolar80
Pending Completion (c)
Wyoming Electric (d)
PPAHappy JackWind30September 3, 2028
Wyoming Electric (e)
PPASilver SageWind30September 30, 2029
_____________
(a)    Colorado Electric sells the wind energy purchased under this PPA to City of Colorado Springs as discussed below.
(b)    This is a firm point-to-point transmission service agreement that provides 50 MW of capacity and energy to be transmitted annually.
(c)    This agreement relates to a new solar facility currently being constructed and will expire 20 years after construction completion, which is expected by the end of 2022.
(d)    Under a separate intercompany PSA, Wyoming Electric sells 50% of the facility output to South Dakota Electric.
(e)    Under a separate intercompany PSA, Wyoming Electric sells 67% of the facility output to South Dakota Electric.
Power purchased  
Long-term Purchase Commitment [Line Items]  
Long-term Purchase Commitment
Costs under these agreements for the years ended December 31 were as follows (in thousands):
SubsidiaryContract TypeCounterpartyFuel Type202020192018
Colorado ElectricPPAPRPAWind$2,791 $— $— 
Colorado ElectricPPAPRPACoal$4,524 $1,802 $— 
South Dakota ElectricPPAPacifiCorpCoal$5,897 $7,477 $13,681 
South Dakota ElectricTSAPacifiCorpN/A$1,776 $1,741 $1,742 
South Dakota ElectricPPAPRPAWind$715 $688 $223 
Wyoming ElectricPPAHappy JackWind$4,531 $3,936 $3,884 
Wyoming ElectricPPASilver SageWind$6,203 $5,366 $5,376 
Purchased Gas Cost Obligation  
Long-term Purchase Commitment [Line Items]  
Long-term Purchase Commitment At December 31, 2020, the long-term commitments to purchase quantities of natural gas under contracts indexed to the following forward indices were as follows (in MMBtus):
Northern Natural Gas - VenturaNorthwest Pipeline - WyomingONEOK - OklahomaSouthern Star Central Gas PipelinePanhandle Eastern Pipe Line
20213,650,0001,510,0005,475,000113,1304,680
20221,810,0001,510,0005,475,000——
20231,840,0001,510,0005,475,000——
20241,820,000910,0005,490,000——
2025——4,560,000——
Thereafter—————