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REVENUE
 9 Months Ended
Sep. 30, 2026
Revenue from Contract with Customer [Abstract]  
REVENUE REVENUE
Revenue from Contracts with Customers
Tri-State's electric sales revenues are derived from wholesale electric service sales to the Utility Members and non-member purchasers.
Member electric sales.
Tri-State's Class A rate schedule (A-41) for power sales to the Utility Members on file with FERC includes a formulary rate, which can be adjusted annually based on the budget approved by Tri-State's Board, including an annual true-up mechanism. Tri-State's A-41 rate includes energy and demand components.
Energy and demand have the same pattern of transfer to the Utility Members and are both measurements of the power provided to the Utility Members. Therefore, the provision of power to Utility Members is one performance obligation. Prior to Utility Members’ requirement for power, Tri-State does not have a contractual right to consideration as Tri-State is not obligated to provide power until the Utility Member requires each incremental unit of power. Tri-State transfers control of the power to Utility Members over time and Utility Members simultaneously receive and consume the benefits of the power. Progress toward completion of Tri-State's performance obligation is measured using the output method: meter readings are taken at the end of each month for billing purposes, energy and demand are determined after the meter readings and Utility Members are invoiced based on the meter reading. Payments from Utility Members are received in accordance with the wholesale electric service contracts’ terms, which is less than 30 days from the invoice date. Utility Member electric sales revenue is recorded as Utility Member electric sales on Tri-State's consolidated statements of operations and Accounts receivable – Utility Members on Tri-State's consolidated statements of financial position.
In addition to Utility Member electric sales, Tri-State has non-member electric sales, transmission revenue and other operating revenue which consist of several revenue streams. On April 1, 2026, certain of Tri-State's load and transmission facilities in the Western Interconnection became part of Southwest Power Pool's ("SPP") expansion of its regional transmission organization into the Western Interconnection. Certain of Tri-State's load and generating facilities participate in SPP's integrated
marketplace. The following revenue is reflected on Tri-State's consolidated statements of operations as follows (dollars in thousands):
Three Months Ended September 30,Nine Months Ended September 30,
2026202520262025
Non-member electric sales:
Long-term contracts$44,766 $39,011 $136,900 $114,284 
Short-term contracts47,787 15,478 67,820 33,108 
Rate stabilization16,491 57,343 50,700 145,469 
Provision for rate refunds(28,320)— (39,893)2,719 
Transmission revenue51,633 25,771 128,746 60,769 
Lease revenue12,602 7,771 36,529 22,329 
Coal sales— 1,249 — 13,714 
Other1,028 5,115 5,253 11,024 
Total non-member electric sales and other operating revenue$145,987 $151,738 $386,055 $403,416 
Non-member electric sales
Revenues from wholesale power sales to non-members are primarily from long-term contracts and short-term market sales. Prior to Tri-State's customers’ demand for energy, Tri-State does not have a contractual right to consideration as it is not obligated to provide energy until the customer demands each incremental unit of energy. Tri-State transfers control of the energy to its customer over time and its customer simultaneously receives and consumes the benefits of the power. Progress toward completion of Tri-State's performance obligation is measured using the output method. Payments are received in accordance with the contract terms, which is less than 30 days after the invoice is received by the customer.
Rate Stabilization
Rate stabilization represents revenue recognition from withdrawal of former Utility Members from membership in Tri-State that was previously deferred in accordance with accounting requirements related to regulated operations. Tri-State recognized $50.7 million of deferred membership withdrawal income for the nine months ended September 30, 2026 compared to $145.5 million of deferred membership withdrawal income being recognized for the nine months ended September 30, 2025.
Provision for Rate Refunds
Tri-State is subject to ongoing proceedings at FERC regarding the return on equity and other inputs used in transmission rates of transmission owners under the SPP's OATT related to the expansion of SPP's regional transmission organization into the Western Interconnection. FERC accepted proposed rates subject to refund and established hearing and settlement procedures. These settlement discussions are ongoing and the matter has not been fully resolved. Pending the ultimate outcome of settlement discussions, Tri-State has recorded an estimated provision for rate refund for such amounts that are subject to refund to transmission customers.
Lease Revenue
Lease revenue is from lease agreements where Tri-State is the lessor primarily for certain generation facilities with third parties. Tri-State has tolling agreements with third parties for certain combustion turbine units at Knutson, Pyramid and Limon Generating Stations that were determined to be leases as the third parties have the right to the economic benefits of applicable unit and the third parties control the use of such unit by its contractual rights, including the ability to direct the timing of dispatch of energy. See Note 15 - Leases.
Transmission revenue
Transmission revenue is received for reservation of capacity or transmission of electricity over Tri-State's transmission facilities, including revenue from SPP related to Tri-State's transmission facilities. Each of these services are provided over time and progress toward completion of Tri-State's performance obligations is measured using the output method.
Other operating revenue
Other operating revenue includes income from various dark fiber agreements that Tri-State has with third parties for the use of certain of Tri-State's telecommunication assets and sales of excess intangible assets.