Tri-State Generation & Transmission Association 10-Q 12 Nov 20 2020 Q3 Quarterly report Financial data

Document and Entity Information

Document and Entity Information	9 Months Ended
	Sep. 30, 2020shares
Document and Entity Information
Document Type	10-Q
Document Period End Date	Sep. 30, 2020
Entity Registrant Name	Tri-State Generation & Transmission Association, Inc.
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Non-accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding	0
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	Q3
Entity Central Index Key	0001637880
Amendment Flag	false

Consolidated Statements of Fina

Consolidated Statements of Financial Position - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Electric plant
In service	$ 6,184,657	$ 6,090,392
Construction work in progress	130,651	164,924
Total electric plant	6,315,308	6,255,316
Less allowances for depreciation and amortization	(2,975,735)	(2,641,470)
Net electric plant	3,339,573	3,613,846
Other plant	415,015	409,051
Less allowances for depreciation, amortization and depletion	(133,587)	(113,607)
Net other plant	281,428	295,444
Total property, plant and equipment	3,621,001	3,909,290
Other assets and investments
Investments in other associations	159,187	161,945
Investments in and advances to coal mines	19,558	19,681
Restricted cash and investments	4,887	30,516
Other noncurrent assets	8,825	8,654
Total other assets and investments	192,457	220,796
Current assets
Cash and cash equivalents	164,965	83,070
Restricted cash and investments	199	182
Deposits and advances	31,586	28,434
Accounts receivable—Utility Members	99,420	105,371
Other accounts receivable	25,198	28,039
Coal inventory	55,879	50,191
Materials and supplies	93,342	93,632
Total current assets	470,589	388,919
Deferred charges
Regulatory assets	717,177	497,279
Prepayment—NRECA Retirement Security Plan	22,833	26,862
Other	58,670	42,672
Total deferred charges	798,680	566,813
Total assets	5,082,727	5,085,818
Capitalization
Patronage capital equity	1,029,050	1,031,063
Accumulated other comprehensive loss	(7,604)	(1,518)
Noncontrolling interest	113,425	111,717
Total equity	1,134,871	1,141,262
Long-term debt	3,205,904	3,063,351
Total capitalization	4,340,775	4,204,613
Current liabilities
Utility Member advances	16,504	18,025
Accounts payable	105,786	99,033
Short-term borrowings		252,323
Accrued expenses	29,165	43,761
Current asset retirement obligations	2,840	2,460
Accrued interest	45,830	29,716
Accrued property taxes	28,086	29,129
Current maturities of long-term debt	87,178	81,555
Total current liabilities	315,389	556,002
Deferred credits and other liabilities
Regulatory liabilities	237,187	122,169
Deferred income tax liability	33,744	58,937
Asset retirement and environmental reclamation obligations	80,303	76,454
Other	56,477	56,399
Total deferred credits and other liabilities	407,711	313,959
Accumulated postretirement benefit and postemployment obligations	18,852	11,244
Total equity and liabilities	$ 5,082,727	$ 5,085,818

Consolidated Statements of Oper

Consolidated Statements of Operations - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Operating revenues
Other	$ 16,226	$ 12,128	$ 37,150	$ 39,540
Operating revenues	401,601	399,053	1,034,723	1,053,558
Operating expenses
Purchased power	103,136	103,525	260,804	252,948
Fuel	65,061	67,374	165,679	204,271
Production	39,698	48,619	122,595	148,457
Transmission	43,989	42,305	127,175	122,329
General and administrative	17,081	12,978	49,337	35,887
Depreciation, amortization and depletion	45,775	40,590	137,110	116,879
Coal mining	4,200	1,675	8,021	7,824
Other	2,691	4,640	13,429	12,154
Operating expenses	321,631	321,706	884,150	900,749
Operating margins	79,970	77,347	150,573	152,809
Other income
Interest	959	1,364	3,248	4,156
Capital credits from cooperatives	1,186	1,186	4,674	4,520
Other income (expense)	197	14,314	348	16,226
Total other income	2,342	16,864	8,270	24,902
Interest expense
Interest	37,673	39,991	114,533	120,754
Interest charged during construction	(1,460)	(1,961)	(5,022)	(6,800)
Interest expense, net of amounts capitalized	36,213	38,030	109,511	113,954
Income tax benefit	(154)	(77)	(484)	(231)
Net margins including noncontrolling interest	46,253	56,258	49,816	63,988
Net margin attributable to noncontrolling interest	(1,424)	(1,113)	(4,164)	(3,239)
Net margins attributable to the Association	44,829	55,145	45,652	60,749
Utility Member electric sales
Operating revenues
Operating revenues	346,769	358,586	926,529	942,175
Non-member electric sales
Operating revenues
Operating revenues	$ 38,606	$ 28,339	$ 71,044	$ 71,843

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Consolidated Statements of Comprehensive Income
Net margins including noncontrolling interest	$ 46,253	$ 56,258	$ 49,816	$ 63,988
Other comprehensive loss:
Amortization of actuarial (gain) loss on postretirement benefit obligation included in net margin	177	(10)	1,287	13
Unrecognized prior service cost			(7,373)	(214)
Other comprehensive loss	177	(10)	(6,086)	(201)
Comprehensive income including noncontrolling interest	46,430	56,248	43,730	63,787
Net comprehensive income attributable to noncontrolling interest	(1,424)	(1,113)	(4,164)	(3,239)
Comprehensive income attributable to the Association	$ 45,006	$ 55,135	$ 39,566	$ 60,548

Consolidated Statements of Equi

Consolidated Statements of Equity - USD ($) $ in Thousands	Patronage capital	Accumulated other comprehensive income (loss)	Noncontrolling interest	Total
Equity at beginning of period at Dec. 31, 2018	$ 1,015,754	$ 375	$ 110,169
Change in Equity
Net margins attributable to the Association	60,749			$ 60,749
Amortization of prior service cost		13		13
Unrecognized prior service cost		(214)		(214)
Net comprehensive income attributable to noncontrolling interest			3,239	3,239
Equity distribution to noncontrolling interest			(2,806)
Equity at end of period at Sep. 30, 2019	1,076,503	174	110,602	1,187,279
Equity at beginning of period at Jun. 30, 2019	1,021,358	184	110,841
Change in Equity
Net margins attributable to the Association	55,145			55,145
Amortization of prior service cost		(10)		(10)
Net comprehensive income attributable to noncontrolling interest			1,113	1,113
Equity distribution to noncontrolling interest			(1,352)
Equity at end of period at Sep. 30, 2019	1,076,503	174	110,602	1,187,279
Equity at beginning of period at Dec. 31, 2019	1,031,063	(1,518)	111,717	1,141,262
Change in Equity
Net margins attributable to the Association	45,652			45,652
Retirement of patronage capital	(47,665)
Amortization of prior service cost		1,287		1,287
Unrecognized prior service cost		(7,373)		(7,373)
Net comprehensive income attributable to noncontrolling interest			4,164	4,164
Equity distribution to noncontrolling interest			(2,456)
Equity at end of period at Sep. 30, 2020	1,029,050	(7,604)	113,425	1,134,871
Equity at beginning of period at Jun. 30, 2020	984,221	(7,781)	113,189
Change in Equity
Net margins attributable to the Association	44,829			44,829
Amortization of prior service cost		177		177
Net comprehensive income attributable to noncontrolling interest			1,424	1,424
Equity distribution to noncontrolling interest			(1,188)
Equity at end of period at Sep. 30, 2020	$ 1,029,050	$ (7,604)	$ 113,425	$ 1,134,871

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Operating activities
Net margins including noncontrolling interest	$ 49,816	$ 63,988
Adjustments to reconcile net margins to net cash provided by operating activities:
Depreciation, amortization and depletion	137,110	116,879
Amortization of intangible asset		3,662
Amortization of NRECA Retirement Security Plan prepayment	4,029	4,029
Amortization of debt issuance costs	1,832	1,773
Impairment loss	259,761	37,067
Deferred impairment loss and other closure costs	(268,163)	(37,067)
Deferred membership withdrawal income	110,165
Capital credit allocations from cooperatives and income from coal mines over refund distributions	2,813	(486)
Changes in operating assets and liabilities:
Accounts receivable	5,844	(155)
Coal inventory	(5,688)	3,922
Materials and supplies	290	(2,943)
Accounts payable and accrued expenses	9,337	3,418
Accrued interest	16,113	15,691
Accrued property taxes	(1,043)	(282)
Other	(16,323)	(7,581)
Net cash provided by operating activities	305,893	201,915
Investing activities
Purchases of plant	(100,821)	(149,396)
Sale of electric plant	26,000
Changes in deferred charges	(4,532)	(6,277)
Proceeds from other investments	68	65
Net cash used in investing activities	(79,285)	(155,608)
Financing activities
Changes in Utility Member advances	(1,520)	(5,351)
Payments of long-term debt	(277,119)	(91,884)
Proceeds from issuance of long-term debt	425,000	34,910
Debt issuance costs	(637)	(13)
Increase (decrease) in short-term borrowings, net	(252,323)	23,036
Retirement of patronage capital	(60,991)	(11,101)
Equity distribution to noncontrolling interest	(2,456)	(2,806)
Other	(279)	(257)
Net cash used in financing activities	(170,325)	(53,466)
Net increase (decrease) in cash, cash equivalents and restricted cash and investments	56,283	(7,159)
Cash, cash equivalents and restricted cash and investments – beginning	113,768	127,590
Cash, cash equivalents and restricted cash and investments – ending	170,051	120,431
Supplemental cash flow information:
Cash paid for interest	97,218	103,782
Supplemental disclosure of noncash investing and financing activities:
Change in plant expenditures included in accounts payable	$ 2,217	$ (873)

PRESENTATION OF FINANCIAL INFOR

PRESENTATION OF FINANCIAL INFORMATION	9 Months Ended
	Sep. 30, 2020
PRESENTATION OF FINANCIAL INFORMATION
PRESENTATION OF FINANCIAL INFORMATION	NOTE 1 – PRESENTATION OF FINANCIAL INFORMATION The accompanying unaudited consolidated financial statements have been prepared in accordance with accounting principles generally accepted in the United States (“GAAP”) for interim financial information and pursuant to the rules and regulations of the Securities and Exchange Commission (“SEC”). Accordingly, they do not include all of the information and footnotes required by GAAP for complete financial statements. These unaudited consolidated financial statements should be read in conjunction with the financial statements and notes thereto included in our annual report on Form 10-K for the year ended December 31, 2019 filed with the SEC. In the opinion of management, all adjustments, consisting of normal recurring accruals considered necessary for a fair presentation, have been included. Our consolidated financial position as of September 30, 2020, results of operations for the three and nine months ended September 30, 2020 and 2019, and cash flows for the nine months ended September 30, 2020 and 2019 are not necessarily indicative of the results that may be expected for an entire year or any other period. Basis of Consolidation We are a taxable wholesale electric power generation and transmission cooperative operating on a not-for-profit basis serving large portions of Colorado, Nebraska, New Mexico and Wyoming. We were incorporated under the laws of the State of Colorado in 1952. We have three classes of membership: Class A - utility full requirements members, Class B - utility partial requirements members, and non-utility members. We have forty-two electric distribution member systems who are Class A members (“Class A Member(s)”) to which we provide electric power pursuant to long-term wholesale electric service contracts. We currently have no Class B members. We have three non-utility members (“Non-Utility Members”). Our Class A Members and any Class B members are collectively referred to as our “Utility Members.” Our Class A Members, any Class B members, and Non-Utility Members are collectively referred to as our “Members.” The addition of Non-Utility Members in 2019 and specifically the addition of MIECO, Inc. on September 3, 2019 removed the exemption from the Federal Energy Regulatory Commission’s (“FERC”) regulation for us, thus subjecting us to full rate and transmission jurisdiction by FERC effective September 3, 2019. Our stated rate to our Class A Members was filed at FERC on December 23, 2019 and was accepted by FERC on March 20, 2020. We comply with the Uniform System of Accounts as prescribed by FERC. In conformity with GAAP, the accounting policies and practices applied by us in the determination of rates are also employed for financial reporting purposes. The accompanying financial statements reflect the consolidated accounts of Tri-State Generation and Transmission Association, Inc. (“Tri-State”, “we”, “our”, “us” or “the Association”), our wholly-owned and majority-owned subsidiaries, and certain variable interest entities for which we or our subsidiaries are the primary beneficiaries. See Note 17 – Variable Interest Entities. Our consolidated financial statements also include our undivided interests in jointly owned facilities. We have eliminated all significant intercompany balances and transactions in consolidation. Jointly Owned Facilities We own undivided interests in two jointly owned generation facilities that are operated by the operating agent of each facility under joint facility ownership agreements with other utilities as tenants in common. These projects include the Yampa Project (operated by us) and the Missouri Basin Power Project (“MBPP”) (operated by Basin Electric Power Cooperative (“Basin”)). Each participant in these agreements receives a portion of the total output of the generation facilities, which approximates its percentage ownership. Each participant provides its own financing for its share of each facility and accounts for its share of the cost of each facility. The operating agent for each of these projects allocates the fuel and operating expenses to each participant based upon its share of the use of the facility. Therefore, our share of the plant asset cost, interest, depreciation and other operating expenses is included in our consolidated financial statements. Our share in each jointly owned facility is as follows as of September 30, 2020 (dollars in thousands): Electric Construction Tri-State Plant in Accumulated Work In Share Service Depreciation Progress Yampa Project - Craig Generating Station Units 1 and 2 24.00 % $ 395,099 $ 249,804 $ 334 MBPP - Laramie River Station 27.13 % 489,147 301,561 5,075 Total $ 884,246 $ 551,365 $ 5,409

ACCOUNTING FOR RATE REGULATION

ACCOUNTING FOR RATE REGULATION	9 Months Ended
	Sep. 30, 2020
ACCOUNTING FOR RATE REGULATION
ACCOUNTING FOR RATE REGULATION	NOTE 2 – ACCOUNTING FOR RATE REGULATION We are subject to the accounting requirements related to regulated operations. In accordance with these accounting requirements, some revenues and expenses have been deferred at the discretion of our Board of Directors (“Board”) if based on regulatory orders or other available evidence, it is probable that these amounts will be refunded or recovered through future rates. Regulatory assets are costs that we expect to recover from our Utility Members based on rates approved by the applicable authority. Regulatory liabilities represent probable future reductions in rates associated with amounts that are expected to be refunded to our Utility Members based on rates approved by the applicable authority. Prior to September 3, 2019, our Board had sole budgetary and rate-setting authority. On September 3, 2019, we became a FERC jurisdictional public utility and our Board’s rate setting authority, including the use of regulatory assets and liabilities, is now subject to FERC approval. Expected recovery of deferred costs and returning deferred credits are based on specific ratemaking decisions by FERC or precedent for each item. We recognize regulatory assets as expenses and regulatory liabilities as operating revenue, other income, or a reduction in expense concurrent with their recovery through rates. Regulatory assets and liabilities are as follows (dollars in thousands): September 30, December 31, 2020 2019 Regulatory assets Deferred income tax expense (1) $ 33,744 $ 58,937 Deferred prepaid lease expense – Springerville Unit 3 Lease (2) 81,996 83,714 Goodwill – J.M. Shafer (3) 47,008 49,145 Goodwill – Colowyo Coal (4) 36,419 37,194 Deferred debt prepayment transaction costs (5) 134,459 140,931 Deferred Holcomb expansion impairment loss (6) 89,988 93,494 Unrecovered plant (7) 293,563 33,864 Total regulatory assets 717,177 497,279 Regulatory liabilities Interest rate swap - realized gain (8) 3,391 3,744 Deferred revenues (9) 75,853 75,853 Membership withdrawal (10) 157,943 42,572 Total regulatory liabilities 237,187 122,169 Net regulatory asset $ 479,990 $ 375,110 (1) A regulatory asset or liability associated with deferred income taxes generally represents the future increase or decrease in income taxes payable that will be received or settled through future rate revenues. (2) Represents deferral of the loss on acquisition related to the Springerville Generating Station Unit 3 (“Springerville Unit 3”) prepaid lease expense upon acquiring a controlling interest in the Springerville Unit 3 Partnership LP (“Springerville Partnership”) in 2009. The regulatory asset for the deferred prepaid lease expense is being amortized to depreciation, amortization and depletion expense in the amount of $2.3 million annually through the 47-year period ending in 2056 and recovered from our Utility Members through rates. (3) Represents goodwill related to our acquisition of Thermo Cogeneration Partnership, LP in December 2011. Goodwill is being amortized to depreciation, amortization and depletion expense in the amount of $2.8 million annually through the 25-year period ending in 2036 and recovered from our Utility Members through rates. (4) Represents goodwill related to our acquisition of Colowyo Coal Company LP (“Colowyo Coal”) in December 2011. Goodwill is being amortized to depreciation, amortization and depletion expense in the amount of $1.0 million annually through the 44-year period ending in 2056 and recovered from our Utility Members through rates. (5) Represents transaction costs that we incurred related to the prepayment of our long-term debt in 2014. These costs are being amortized to depreciation, amortization and depletion expense in the amount of $8.6 million annually over the 21.4-year period ending in 2036 and recovered from our Utility Members through rates. (6) Represents deferral of the impairment loss related to development costs, including costs for the option to purchase development rights for the expansion of the Holcomb Generating Station. Beginning January 2020, the deferred impairment loss is being amortized to depreciation, amortization and depletion expense in the amount of $4.7 million annually over the 20-year period ending in 2039 and recovered from our Utility Members through rates. (7) Represents deferral of the impairment losses related to the early retirement of the Nucla and Escalante Generating Stations. In July 2019, our Board took action for the early retirement of the Nucla Generating Station and the deferral of any impairment loss in accordance with accounting for rate regulation. In conjunction with the early retirement of the Nucla Generating Station, we recognized an impairment loss of $37.1 million during the third quarter of 2019. On September 19, 2019, the Nucla Generating Station was officially retired from service. The deferred impairment loss for Nucla Generating Station is being amortized to depreciation, amortization and depletion expense over the 3.3-year period ending in December 2022 and recovered from our Utility Members through rates. In January 2020, our Board approved the early retirement of the Escalante Generating Station and the deferral of any impairment loss in accordance with accounting for rate regulation. In conjunction with the early retirement, we recognized an impairment loss of $268.2 million during the first quarter of 2020. The deferred impairment loss for Escalante Generating Station will be amortized to depreciation, amortization and depletion expense beginning in 2021 through the end of 2045, which was the depreciable life of Escalante Generating Station, and is expected to be recovered from our Utility Members through rates. The annual amortization is expected to approximate the former annual Escalante Generating Station depreciation for the remaining life of the asset. (8) Represents deferral of a realized gain of $4.6 million related to the October 2017 settlement of a forward starting interest rate swap. This realized gain was deferred as a regulatory liability and is being amortized to interest expense over the 12-year term of the First Mortgage Obligations, Series 2017A and refunded to Utility Members through reduced rates when recognized in future periods. (9) Represents deferral of the recognition of non-member electric sales revenues. These deferred non-member electric sales revenues will be refunded to Utility Members through reduced rates when recognized in non-member electric sales revenue in future periods. (10) Represents the deferral of the recognition of other income related to the June 30, 2016 withdrawal of a former Utility Member from membership in us and the June 30, 2020 withdrawal of Delta-Montrose Electric Association (“DMEA”) from membership in us. In connection with the DMEA withdrawal, we recognized $110.2 million of other income and $5.2 million of gain on sale of assets which was subsequently deferred. The total deferred membership withdrawal income will be refunded to Utility Members through reduced rates, subject to FERC approval, when recognized in other income in future periods.

INVESTMENTS IN OTHER ASSOCIATIO

INVESTMENTS IN OTHER ASSOCIATIONS	9 Months Ended
	Sep. 30, 2020
INVESTMENTS IN OTHER ASSOCIATIONS
INVESTMENTS IN OTHER ASSOCIATIONS	NOTE 3 – INVESTMENTS IN OTHER ASSOCIATIONS Investments in other associations include investments in the patronage capital of other cooperatives and other required investments in the organizations. Our investment in a cooperative increases when a cooperative allocates patronage capital credits to us and it decreases when we receive a cash retirement of the allocated capital credits from the cooperative. A cooperative allocates its patronage capital credits to us based upon our patronage (amount of business done) with the cooperative. Investments in other associations are as follows (dollars in thousands): September 30, December 31, 2020 2019 Basin Electric Power Cooperative $ 114,036 $ 117,368 National Rural Utilities Cooperative Finance Corporation - patronage capital 11,933 11,761 National Rural Utilities Cooperative Finance Corporation - capital term certificates 15,885 15,953 CoBank, ACB 11,141 10,201 Western Fuels Association, Inc. 2,302 2,409 Other 3,890 4,253 Investments in other associations $ 159,187 $ 161,945 Our investments in other associations are considered equity securities without readily determinable fair values, and as such are measured at cost minus impairment. We have evaluated these investments for indicators of impairment. There were no impairments of these investments recognized during the nine months ended September 30, 2020 or during 2019.

INVESTMENTS IN AND ADVANCES TO

INVESTMENTS IN AND ADVANCES TO COAL MINES	9 Months Ended
	Sep. 30, 2020
INVESTMENTS IN AND ADVANCES TO COAL MINES
INVESTMENTS IN AND ADVANCES TO COAL MINES	NOTE 4 – INVESTMENTS IN AND ADVANCES TO COAL MINES We have direct ownership and investments in coal mines to support our coal generating resources. We, and certain participants in the Yampa Project, are members of Trapper Mining, which is organized as a cooperative and is the owner and operator of the Trapper Mine near Craig, Colorado. Our investment in Trapper Mining is recorded using the equity method. In addition, we have ownership in Western Fuels Association, Inc. (“WFA”), which is an owner of Western Fuels‑Wyoming, Inc. (“WFW”), the owner and operator of the Dry Fork Mine near Gillette, Wyoming. Dry Fork Mine provides coal to the Laramie River Generating Station (owned by the participants of MBPP). We, through our undivided interest in the jointly owned facility of MBPP, advance funds to the Dry Fork Mine. Investments in and advances to coal mines are as follows (dollars in thousands): September 30, December 31, 2020 2019 Investment in Trapper Mine $ 16,279 $ 15,881 Advances to Dry Fork Mine 3,279 3,800 Investments in and advances to coal mines $ 19,558 $ 19,681

CASH, CASH EQUIVALENTS AND REST

CASH, CASH EQUIVALENTS AND RESTRICTED CASH AND INVESTMENTS	9 Months Ended
	Sep. 30, 2020
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents [Abstract]
CASH, CASH EQUIVALENTS AND RESTRICTED CASH AND INVESTMENTS	NOTE 5 – CASH, CASH EQUIVALENTS AND RESTRICTED CASH AND INVESTMENTS We consider highly liquid investments with an original maturity of three months or less to be cash equivalents. The fair value of cash equivalents approximates their carrying values due to their short-term maturity. Restricted cash and investments represent funds designated by our Board for specific uses and funds restricted by contract or other legal reasons. A portion of the funds are amounts that have been restricted by contract that are expected to be settled within one year. These funds are therefore classified as current on our consolidated statements of financial position. The other funds are for amounts restricted by contract or other legal reasons that are expected to be settled beyond one year. These funds are classified as noncurrent and are included in other assets and investments on our consolidated statements of financial position. The following table provides a reconciliation of cash, cash equivalents and restricted cash and investments reported within our consolidated statements of financial position that sum to the total of the same such amount shown in our consolidated statements of cash flows (dollars in thousands): September 30, December 31, 2020 2019 Cash and cash equivalents $ 164,965 $ 83,070 Restricted cash and investments - current 199 182 Restricted cash and investments - noncurrent 4,887 30,516 Cash, cash equivalents and restricted cash and investments $ 170,051 $ 113,768 Our Board Policy for Financial Goals and Capital Credits was revised in 2018 to provide that our Board will endeavor to fund an internally restricted cash account for the purpose of cash funding deferred revenues and incomes held as regulatory liabilities. In connection with such policy, our Board internally restricted cash in the amount of $25.5 million as of December 31, 2019 which was included in restricted cash and investments - noncurrent. Our Board may, at any time and for any reason, unrestrict any internally restricted cash. On March 10, 2020, our Board took action to unrestrict the $25.5 million balance of the restricted cash in response to volatile market conditions.

CONTRACT ASSETS AND CONTRACT LI

CONTRACT ASSETS AND CONTRACT LIABILITIES	9 Months Ended
	Sep. 30, 2020
CONTRACT ASSETS AND CONTRACT LIABILITIES
CONTRACT ASSETS AND CONTRACT LIABILITIES	NOTE 6 – CONTRACT ASSETS AND CONTRACT LIABILITIES Accounts Receivable We record accounts receivable for our unconditional rights to consideration arising from our performance under contracts with our Members and other parties. Uncollectible amounts, if any, are identified on a specific basis and charged to expense in the period determined to be uncollectible. See Note 13 – Revenue. Contract liabilities (unearned revenue) A contract liability represents an entity’s obligation to transfer goods or services to a customer for which the entity has received consideration from the customer. We have received deposits from others and these deposits are reflected in unearned revenue (included in other deferred credits and other liabilities on our consolidated statements of financial position) before revenue is recognized, resulting in contract liabilities. During the nine months ended September 30, 2020, we recognized $0.9 million of this unearned revenue in other operating revenues on our consolidated statements of operations. Our contract assets and liabilities consist of the following (dollars in thousands): September 30, December 31, 2020 2019 Accounts receivable - Utility Members $ 99,420 $ 105,371 Other accounts receivable - trade: Non-member electric sales 7,900 4,727 Other 16,615 20,628 Total other accounts receivable - trade 24,515 25,355 Other accounts receivable - nontrade 683 2,684 Total other accounts receivable $ 25,198 $ 28,039 Contract liabilities (unearned revenue) $ 6,281 $ 7,041

OTHER DEFERRED CHARGES

OTHER DEFERRED CHARGES	9 Months Ended
	Sep. 30, 2020
OTHER DEFERRED CHARGES.
OTHER DEFERRED CHARGES	NOTE 7 – OTHER DEFERRED CHARGES The following other deferred charges are reflected on our consolidated statements of financial position (dollars in thousands): September 30, December 31, 2020 2019 Preliminary surveys and investigations $ 23,012 $ 21,261 Advances to operating agents of jointly owned facilities 8,686 3,917 Operating lease right-of-use assets 10,086 7,622 Other 16,886 9,872 Total other deferred charges $ 58,670 $ 42,672 We make expenditures for preliminary surveys and investigations for the purpose of determining the feasibility of contemplated generation and transmission projects. If construction results, the preliminary survey and investigation expenditures will be reclassified to electric plant ‑ construction work in progress. If the work is abandoned, the related preliminary survey and investigation expenditures will be charged to the appropriate operating expense account or the expense could be deferred as a regulatory asset to be recovered from our Utility Members through rates subject to approval by our Board and FERC. We make advance payments to the operating agents of jointly owned facilities to fund our share of costs expected to be incurred under each project including MBPP – Laramie River Station, and Yampa Project – Craig Generating Station Units 1 and 2. We also make advance payments to the operating agent of Springerville Unit 3. A right-of-use asset represents a lessee’s right to control the use of the underlying asset for the lease term. Right-of-use assets are included in other deferred charges and presented net of accumulated amortization. See Note 15 – Leases.

LONG-TERM DEBT

LONG-TERM DEBT	9 Months Ended
	Sep. 30, 2020
LONG-TERM DEBT.
LONG-TERM DEBT	NOTE 8 – LONG-TERM DEBT We have $3.2 billion of long-term debt which consists of mortgage notes payable, pollution control revenue bonds and the Springerville certificates. The mortgage notes payable and pollution control revenue bonds are secured on a parity basis by a Master First Mortgage Indenture, Deed of Trust and Security Agreement (“Master Indenture”) except for one unsecured note in the amount of $21.5 million as of September 30, 2020. Substantially all our assets, rents, revenues and margins are pledged as collateral. The Springerville certificates are secured by the assets of Springerville Unit 3. All long-term debt contains certain restrictive financial covenants, including a debt service ratio requirement on an annual basis and an equity to capitalization ratio requirement of at least 18 percent at the end of each fiscal year. Other than the Springerville certificates that has a debt service ratio requirement of at least 1.02 on an annual basis, all other long-term debt contains a debt service ratio requirement of at least 1.10 on an annual basis. We have a secured revolving credit facility with National Rural Utilities Cooperative Finance Corporation (“CFC”), as lead arranger and administrative agent, in the amount of $650 million (“Revolving Credit Agreement”) that expires on April 25, 2023 and includes a swingline sublimit of $100 million, a letter of credit sublimit of $75 million, and a commercial paper back-up sublimit of $500 million. As of September 30, 2020, we had $650.0 million in availability under the Revolving Credit Agreement. Long-term debt consists of the following (dollars in thousands): September 30, December 31, 2020 2019 Total debt $ 3,314,353 3,166,472 Less debt issuance costs (26,218) (27,412) Less debt discounts (9,722) (9,906) Plus debt premiums 14,669 15,752 Total debt adjusted for debt issuance costs, discounts and premiums 3,293,082 3,144,906 Less current maturities (87,178) (81,555) Long-term debt $ 3,205,904 $ 3,063,351

SHORT-TERM BORROWINGS

SHORT-TERM BORROWINGS	9 Months Ended
	Sep. 30, 2020
SHORT-TERM BORROWINGS
SHORT-TERM BORROWINGS	NOTE 9 – SHORT-TERM BORROWINGS We have a commercial paper program under which we issue unsecured commercial paper in aggregate amounts not exceeding the commercial paper back-up sublimit under our Revolving Credit Agreement, which is the lesser of $500 million or the amount available under our Revolving Credit Agreement. The commercial paper issuances are used to provide an additional financing source for our short-term liquidity needs. The maturities of the commercial paper issuances vary, but may not exceed 397 days from the date of issue. The commercial paper notes are classified as current and are included in current liabilities as short-term borrowings on our consolidated statements of financial position. Commercial paper consisted of the following (dollars in thousands): September 30, December 31, 2020 2019 Commercial paper outstanding, net of discounts $ — $ 252,323 Weighted average interest rate — % 1.88 % At September 30, 2020, $500.0 million of the commercial paper back-up sublimit remained available under the Revolving Credit Agreement. See Note 8 – Long-Term Debt.

ASSET RETIREMENT OBLIGATIONS

ASSET RETIREMENT OBLIGATIONS	9 Months Ended
	Sep. 30, 2020
ASSET RETIREMENT OBLIGATIONS
ASSET RETIREMENT OBLIGATIONS	NOTE 10 – ASSET RETIREMENT AND ENVIRONMENTAL RECLAMATION OBLIGATIONS We account for current obligations associated with the future retirement of tangible long‑lived assets and environmental reclamation in accordance with the accounting guidance relating to asset retirement and environmental obligations. This guidance requires that legal obligations associated with the retirement of long‑lived assets be recognized at fair value at the time the liability is incurred and capitalized as part of the related long‑lived asset. Over time, the liability is adjusted to its present value by recognizing accretion expense and the capitalized cost of the long‑lived asset is depreciated in a manner consistent with the depreciation of the underlying physical asset. In the absence of quoted market prices, we determine fair value by using present value techniques in which estimates of future cash flows associated with retirement activities are discounted using a credit adjusted risk‑free rate and market risk premium. Upon settlement of an asset retirement obligation, we will apply payment against the estimated liability and incur a gain or loss if the actual retirement costs differ from the estimated recorded liability. Environmental reclamation costs are accrued based on management’s best estimate at the end of each period of the costs expected to be incurred. Such cost estimates may include ongoing care, maintenance and monitoring costs. Changes in reclamation estimates are reflected in earnings in the period an estimate is revised. Estimates of future expenditures for environmental reclamation obligations are not discounted. Coal mines: We have asset retirement obligations for the final reclamation costs and post‑reclamation monitoring related to the Colowyo Mine, the New Horizon Mine, and the Fort Union Mine. The New Horizon Mine is currently in post-reclamation monitoring. One pit at the Colowyo Mine began final reclamation in 2018 with the other remaining pits still being actively mined. Generation: We, including through our undivided interest in jointly owned facilities, have asset retirement obligations related to equipment, dams, ponds, wells and underground storage tanks at the generating stations. Aggregate carrying amounts of asset retirement obligations and environmental reclamation obligations are as follows (dollars in thousands): Nine Months Ended September 30, 2020 Obligations at beginning of period $ 78,914 Liabilities incurred — Liabilities settled (824) Accretion expense 1,895 Change in cash flow estimate 3,158 Total obligations at end of period $ 83,143 Less current obligations at end of period (2,840) Long-term obligations at end of period $ 80,303 We also have asset retirement obligations with indeterminate settlement dates. These are made up primarily of obligations attached to transmission and other easements that are considered by us to be operated in perpetuity and therefore the measurement of the obligation is not possible. A liability will be recognized in the period in which sufficient information exists to estimate a range of potential settlement dates as is needed to employ a present value technique to estimate fair value.

OTHER DEFERRED CREDITS AND OTHE

OTHER DEFERRED CREDITS AND OTHER LIABILITIES	9 Months Ended
	Sep. 30, 2020
OTHER DEFERRED CREDITS AND OTHER LIABILITIES
OTHER DEFERRED CREDITS AND OTHER LIABILITIES	NOTE 11 – OTHER DEFERRED CREDITS AND OTHER LIABILITIES The following other deferred credits and other liabilities are reflected on our consolidated statements of financial position (dollars in thousands): September 30, December 31, 2020 2019 Transmission easements $ 20,148 $ 20,549 Operating lease liabilities - noncurrent 1,705 1,846 Contract liabilities (unearned revenue) - noncurrent 3,781 4,217 Customer deposits 7,404 3,015 Financial liabilities - reclamation 10,217 12,091 Other 13,222 14,681 Total other deferred credits and other liabilities $ 56,477 $ 56,399 In 2015, we renewed transmission right of way easements on tribal nation lands where certain of our electric transmission lines are located. $31.2 million will be paid by us for these easements from 2020 through the individual easement terms ending between 2036 and 2040. The present values for the remaining easement payments were $20.1 and $20.5 million as of September 30, 2020 and December 31, 2019, respectively, which are recorded as other deferred credits and other liabilities. A lease liability represents a lessee’s obligation to make lease payments over the lease term. The long-term portion of our lease liabilities are included in other deferred credits and other liabilities and the current portion of our lease liabilities are included in current liabilities. See Note 15 – Leases. A contract liability represents an entity’s obligation to transfer goods or services to a customer for which the entity has received consideration from the customer. We have received deposits from others and these deposits are reflected in contract liabilities (unearned revenue) until recognized in other operating revenues over the life of the agreement. We have received deposits from various parties and those that may still be required to be returned are a liability and these are reflected in customer deposits.

EMPLOYEE BENEFIT PLANS

EMPLOYEE BENEFIT PLANS	9 Months Ended
	Sep. 30, 2020
EMPLOYEE BENEFIT PLANS
EMPLOYEE BENEFIT PLANS	NOTE 12 – EMPLOYEE BENEFIT PLANS Postretirement Benefits Other Than Pensions We sponsor three medical plans for all non-bargaining unit employees under the age of 65. Two of the plans provide postretirement medical benefits to full-time non-bargaining unit employees and retirees who receive benefits under those plans, who have attained age 55, and who elect to participate. All three of these non-bargaining unit medical plans offer postemployment medical benefits to employees on long-term disability. The plans were unfunded at September 30, 2020, are contributory (with retiree premium contributions equivalent to employee premiums, adjusted annually) and contain other cost-sharing features such as deductibles. The postretirement medical benefit and postemployment medical benefit obligations are determined annually (during the fourth quarter) by an independent actuary and are included in accumulated postretirement benefit and postemployment obligations on our consolidated statements of financial position as follows (dollars in thousands): Nine Months Ended September 30, 2020 Postretirement medical benefit obligation at beginning of period $ 10,195 Service cost 422 Interest cost 264 Benefit payments (net of contributions by participants) (465) Postretirement medical benefit obligation at end of period $ 10,416 Postemployment medical benefit obligation at end of period 375 Total postretirement and postemployment medical obligations at end of period $ 10,791 The service cost component of our net periodic benefit cost is included in operating expenses on our consolidated statements of operations. The components of net periodic benefit cost other than the service cost component are included in other income (expense) on our consolidated statements of operations. In accordance with the accounting standard related to postretirement benefits other than pensions, actuarial gains and losses are not recognized in income but are instead recorded in accumulated other income on our consolidated statements of financial position. If the unrecognized amount is in excess of 10 percent of the projected benefit obligation, amounts are reclassified out of accumulated other comprehensive income and included in net income as the excess is amortized over the average remaining service lives of the active plan participants. Unrecognized actuarial gains and losses have been determined per actuarial studies for the postretirement medical benefit obligation. The net unrecognized actuarial gains and losses related to the postretirement medical benefit obligations are included in accumulated other comprehensive income as follows (dollars in thousands): Nine Months Ended September 30, 2020 Accumulated other comprehensive loss at beginning of period $ (1,387) Amortization of actuarial (gain) loss into income 11 Amortization of prior service credit into other income (59) Accumulated other comprehensive loss at end of period $ (1,435) Defined Benefit Plans We participate in the NRECA Pension Restoration Plan and the NRECA Executive Benefit Restoration Plan, both of which are intended to provide a supplemental benefit to the defined benefit plan for an eligible group of highly compensated employees. Eligible employees include the Chief Executive Officer and any other employees that become eligible. All our executive employees currently participate in one of the following pension restoration plans: the NRECA Pension Restoration Plan or the NRECA Executive Benefit Restoration Plan. Eligibility is determined annually and is based on January 1 base salary that exceeds the limits of the defined benefit plan. The NRECA Executive Benefit Restoration Plan obligations are determined annually (during the first quarter of the subsequent year) by an NRECA actuary and are included in accumulated postretirement benefit and postemployment obligations on our consolidated statements of financial position as follows (dollars in thousands): Nine Months Ended September 30, 2020 Executive benefit restoration obligation at beginning of period $ 674 Service cost 312 Interest cost 417 Plan amendments - prior service cost 5,218 Benefit payments (715) Actuarial loss 2,155 Executive benefit restoration at end of period $ 8,061 The service cost component of our net periodic benefit cost is included in operating expenses on our consolidated statements of operations. The components of net periodic benefit cost other than the service cost component are included in other income (expense) on our consolidated statements of operations. In accordance with the accounting standard related to defined benefit pension plans, actuarial gains and losses are not recognized in income but are instead recorded in accumulated other income on our consolidated statements of financial position. If the unrecognized amount is in excess of 10 percent of the projected benefit obligation, amounts are reclassified out of accumulated other comprehensive income and included in net income as the excess is amortized over the average remaining service lives of the active plan participants. Unrecognized actuarial gains and losses have been determined per actuarial studies for the executive benefit restoration obligation. The net unrecognized actuarial gains and losses related to the executive benefit restoration obligations are included in accumulated other comprehensive income as follows (dollars in thousands): Nine Months Ended September 30, 2020 Accumulated other comprehensive loss at beginning of period $ (130) Plan amendments - prior service cost (5,218) Amortization of prior service cost into other income 1,336 Unrecognized actuarial loss (2,155) Accumulated other comprehensive loss at end of period $ (6,167)

REVENUE

REVENUE	9 Months Ended
	Sep. 30, 2020
REVENUE
REVENUE	NOTE 13 – REVENUE Revenue from Contracts with Customers Our revenues are derived primarily from the sale of electric power to our Utility Members pursuant to long-term wholesale electric service contracts. Our contracts with our 42 Utility Members extend through 2050. We had a contract with DMEA that extended through 2040. DMEA withdrew from membership in us on June 30, 2020 and DMEA’s contract was assigned by us to DMEA’s new third-party power supplier. Member electric sales Revenues from electric power sales to our Utility Members are primarily from our Class A rate schedule filed with FERC. Our Class A rate schedule for electric power sales to our Utility Members consist of three billing components: an energy rate and two demand rates. Our Class A rate schedule is variable and is approved by our Board and FERC. Energy and demand have the same pattern of transfer to our Utility Members and are both measurements of the electric power provided to our Utility Members. Therefore, the provision of electric power to our Utility Members is one performance obligation. Prior to our Utility Members’ requirement for electric power, we do not have a contractual right to consideration as we are not obligated to provide electric power until the Utility Member requires each incremental unit of electric power. We transfer control of the electric power to our Utility Members over time and our Utility Members simultaneously receive and consume the benefits of the electric power. Progress toward completion of our 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 our 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 our consolidated statements of operations and Accounts receivable – Utility Members on our consolidated statements of financial position. In addition to our Utility Member electric sales, we have non-member electric sales and other operating revenue which consist of several revenue streams. The following revenue is reflected on our consolidated statements of operations as follows (dollars in thousands): Three Months Ended September 30, Nine Months Ended September 30, 2020 2019 2020 2019 Non-member electric sales: Long-term contracts $ 9,423 $ 12,647 $ 32,817 $ 35,241 Short-term contracts 29,183 15,692 38,227 36,602 Other 16,226 12,128 37,150 39,540 Total non-member electric sales and other operating revenue $ 54,832 $ 40,467 $ 108,194 $ 111,383 Non-member electric sales Revenues from electric power sales to non-members are primarily from long-term contracts and short-term market sales. Prior to our customers’ demand for energy, we do not have a contractual right to consideration as we are not obligated to provide energy until the customer demands each incremental unit of energy. We transfer control of the energy to our customer over time and our customer simultaneously receives and consumes the benefits of the electric power. Progress toward completion of our 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. Other operating revenue Other operating revenue consists primarily of wheeling, transmission and lease revenues, coal sales and revenue from supplying steam and water. Other operating revenue also includes revenue we receive from two of our Non-Utility Members. Wheeling revenue is earned when we charge other energy companies for transmitting electricity over our transmission lines (payments are received in accordance with the contract terms which is within 20 days of the date the invoice is received). Transmission revenue is from Southwest Power Pool’s scheduling of transmission across our transmission assets in the Eastern Interconnection because of our membership in it (Southwest Power Pool collects the revenue from the customer and pays us for the scheduling, system control, dispatch transmission service, and the annual transmission revenue requirement). Steam and water revenue is derived from supplying steam and water to a paper manufacturer located adjacent to the Escalante Generating Station (payments from the customer are received in accordance with the contract terms which is less than 15 days from the invoice date). Each of these services or goods are provided over time and progress toward completion of our performance obligations are measured using the output method. Lease revenue is primarily from a certain power sales arrangement, which expired on June 30, 2019, that was required to be accounted for as an operating lease since the arrangement conveyed the right to use power generating equipment for a stated period of time. Coal sales revenue results from the sale of coal from the Colowyo Mine to third parties. We have an obligation to deliver coal and progress of completion toward our performance obligation is measured using the output method. Our performance obligation is completed as coal is delivered.

INCOME TAXES

INCOME TAXES	9 Months Ended
	Sep. 30, 2020
INCOME TAXES
INCOME TAXES	NOTE 14 – INCOME TAXES We are a taxable cooperative subject to federal and state taxation. As a taxable electric cooperative, we are allowed a tax exclusion for margins allocated as patronage capital. We utilize the liability method of accounting for income taxes. However, in accordance with our regulatory accounting treatment, changes in deferred tax assets or liabilities result in the establishment of a regulatory asset or liability. A regulatory asset or liability associated with deferred income taxes generally represents the future increase or decrease in income taxes payable that will be settled or received through future rate revenues. Under this regulatory accounting approach, any income tax expense or benefit on our consolidated statements of operations includes only the current provision. This liability method is included in our rate filing accepted by FERC on March 20, 2020; however, FERC may require a different method for the recovery of income taxes. Our consolidated statements of operations included an income tax benefit of $0.5 million for the nine months ended September 30, 2020 and $0.2 million for the comparable period in 2019. These income tax benefits are due to an alternative minimum tax credit refund. During the first quarter of 2020, we recorded a $19 million decrease in our deferred tax asset valuation allowance due to the deferred tax treatment of an abandonment loss. No further changes to the valuation allowance were needed for the nine-month period ended September 30, 2020. The Coronavirus Aid, Relief and Economic Security Act (“CARES Act”) was signed into law on March 27, 2020. The CARES Act includes certain corporate income tax provisions which have been evaluated by us. The CARES Act did not have a material impact on our consolidated financial statements.

LEASES

LEASES	9 Months Ended
	Sep. 30, 2020
LEASES
LEASES	NOTE 15 – LEASES Leasing Arrangements As Lessee We determine if an arrangement is a lease upon commencement of the contract. If an arrangement is determined to be a long-term lease (greater than 12 months), we recognize a right-of-use asset and lease liability based on the present value of the future minimum lease payments over the lease term at the commencement date. As most of our leases do not provide an implicit rate, we use our incremental borrowing rate based on the information available at commencement date in determining the present value of future payments. Our lease terms may also include options to extend or terminate the lease when it is reasonably certain that we will exercise those options. Lease expense for minimum lease payments is recognized on a straight-line basis over the lease term. Right-of-use assets are included in other deferred charges, the current portion of lease liabilities is included in current liabilities and the long-term portion of lease liabilities is included in other deferred credits and other liabilities on our consolidated statements of financial position. We have elected to apply the short-term lease exception for contracts that have a lease term of twelve months or less and do not include an option to purchase the underlying asset. Therefore, we do not recognize a right-of-use asset or lease liability for such contracts. We recognize short-term lease payments as expense on a straight-line basis over the lease term. Variable lease payments that do not depend on an index or rate are recognized as expense. We have lease agreements as lessee for the right to use various facilities and operational assets and had a lease agreement for the right to use power generating equipment at Brush Generating Station. Under the power purchase arrangement at the Brush Generating Station that expired on December 31, 2019, we were required to account for the arrangement as an operating lease since it conveys to us the right to direct the use of 70 megawatts at the Brush Generating Station whereby we provide our own natural gas for generation of electricity. We did not renew this power purchase arrangement. Rent expense for all short-term and long-term operating leases was $1.2 million for the three months ended September 30, 2020 and $1.8 million for the comparable period in 2019. Rent expense for all short-term and long-term operating leases was $2.8 million for the nine months ended September 30, 2020 and $5.4 million for the comparable period in 2019. Rent expense is included in operating expenses on our consolidated statements of operations. As of September 30, 2020, there were no arrangements accounted for as finance leases. Our consolidated statements of financial position include the following lease components (dollars in thousands): September 30, December 31, 2020 2019 Operating leases Operating lease right-of-use assets $ 11,464 $ 8,376 Less: Accumulated amortization (1,378) (754) Net operating lease right-of-use assets $ 10,086 $ 7,622 Operating lease liabilities - current $ (556) $ (5,533) Operating lease liabilities - noncurrent (1,705) (1,846) Total operating lease liabilities $ (2,261) $ (7,379) Operating leases Weighted average remaining lease term (years) Weighted average discount rate Future expected minimum lease commitments under operating leases are as follows (dollars in thousands): Year 1 $ 609 Year 2 444 Year 3 341 Year 4 315 Year 5 196 Thereafter 737 Total lease payments $ 2,642 Less imputed interest (381) Total $ 2,261 Leasing Arrangements As Lessor We have lease agreements as lessor for certain operational assets and had a lease agreement as lessor for power generating equipment at the J.M. Shafer Generating Station. Under the power sales arrangement at the J.M. Shafer Generating Station that expired on June 30, 2019, we were required to account for the arrangement as an operating lease since it conveyed to a third party the right to direct the use of 122 megawatts of the 272 megawatt generating capability of the J.M. Shafer Generating Station whereby the third party provided its own natural gas for generation of electricity. The revenue from these lease agreements of $1.8 million and $1.6 million for the three months ended September 30, 2020 and 2019, respectively, and $5.0 million and $10.5 million for the nine months ended September 30, 2020 and 2019, respectively, are included in other operating revenue on our consolidated statements of operations. The lease arrangement with the Springerville Partnership is not reflected in our lease right right-of-use asset or liability balances as the associated revenues and expenses are eliminated in consolidation. See Note 17- Variable Interest Entities. However, as the noncontrolling interest associated with this lease arrangement generates book-tax differences, a deferred tax asset and liability have been recorded. See Note 14 – Income Taxes.

FAIR VALUE

FAIR VALUE	9 Months Ended
	Sep. 30, 2020
FAIR VALUE
FAIR VALUE	NOTE 16 – FAIR VALUE Fair value is defined as the price that would be received to sell an asset or paid to transfer a liability between market participants in the principal or in the most advantageous market when no principal market exists. The fair value measurement accounting guidance emphasizes that fair value is a market-based measurement, not an entity-specific measurement. Therefore, a fair value measurement should be determined based on the assumptions that market participants would use in pricing the asset or liability (market participants are assumed to be independent, knowledgeable, able and willing to transact an exchange and not under duress). In considering market participant assumptions in fair value measurements, a three-tier fair value hierarchy for measuring fair value was established which prioritizes the inputs used in measuring fair value as follows: Level 1 inputs are based upon quoted prices for identical instruments traded in active (exchange-traded) markets. Valuations are obtained from readily available pricing sources for market transactions (observable market data) involving identical assets or liabilities. Level 2 inputs are based upon quoted prices for similar instruments in active markets, quoted prices for identical or similar instruments in markets that are not active and model-based valuation techniques (such as option pricing models, discounted cash flow models) for which all significant assumptions are observable in the market. Level 3 inputs consist of unobservable market data which is typically based on an entity’s own assumptions of what a market participant would use in pricing an asset or liability as there is little, if any, related market activity. In instances where the determination of the fair value measurement is based on inputs from different levels of the fair value hierarchy, the level in the fair value hierarchy within which the entire fair value measurement falls is based on the lowest level input that is significant to the fair value measurement in its entirety. The assessment of the significance of a particular input to the fair value measurement in its entirety requires judgment and considers factors specific to the asset or liability. Marketable Securities We hold marketable securities in connection with the directors’ and executives’ elective deferred compensation plans which consist of investments in stock funds, bond funds and money market funds. These securities are measured at fair value on a recurring basis with changes in fair value recognized in earnings. The estimated fair value of the investments is based upon their active market value (Level 1 inputs) and is included in other noncurrent assets on our consolidated statements of financial position. The cost and fair values of our marketable securities are as follows (dollars in thousands): September 30, 2020 December 31, 2019 Estimated Estimated Cost Fair Value Cost Fair Value Marketable securities $ 477 $ 429 $ 715 $ 654 Cash Equivalents We invest portions of our cash and cash equivalents in commercial paper, money market funds, and other highly liquid investments. The fair value of these investments approximates our cost basis in the investments. In aggregate, the fair value was $102.2 million as of September 30, 2020 and $79.0 million as of December 31, 2019. Debt The fair values of debt were estimated using discounted cash flow analyses based on our current incremental borrowing rates for similar types of borrowing arrangements. These valuation assumptions utilize observable inputs based on market data obtained from independent sources and are therefore considered Level 2 inputs (quoted prices for similar assets, liabilities (adjusted) and market corroborated inputs). The principal amounts and fair values of our debt are as follows (dollars in thousands): September 30, 2020 December 31, 2019 Principal Estimated Principal Estimated Amount Fair Value Amount Fair Value Total debt $ 3,314,353 $ 3,926,312 $ 3,166,472 $ 3,608,341

VARIABLE INTEREST ENTITIES

VARIABLE INTEREST ENTITIES	9 Months Ended
	Sep. 30, 2020
VARIABLE INTEREST ENTITIES
VARIABLE INTEREST ENTITIES	NOTE 17 – VARIABLE INTEREST ENTITIES The following is a description of our financial interests in variable interest entities that we consider significant. This includes an entity for which we are determined to be the primary beneficiary and therefore consolidate and also entities for which we are not the primary beneficiary and therefore do not consolidate. Consolidated Variable Interest Entity Springerville Partnership: We own a 51 percent equity interest, including the 1 percent general partner equity interest, in the Springerville Partnership, which is the 100 percent owner of Springerville Unit 3 Holding LLC (“Owner Lessor”). The Owner Lessor is the owner of the Springerville Unit 3. We, as general partner of the Springerville Partnership, have the full, exclusive and complete right, power and discretion to operate, manage and control the affairs of the Springerville Partnership and take certain actions necessary to maintain the Springerville Partnership in good standing without the consent of the limited partners. Additionally, the Owner Lessor has historically not demonstrated an ability to finance its activities without additional financial support. The financial support is provided by our remittance of lease payments in order to permit the Owner Lessor, the holder of the Springerville Unit 3 assets, to pay the debt obligations and equity returns of the Springerville Partnership. We have the primary risk (expense) exposure in operating the Springerville Unit 3 assets and are responsible for 100 percent of the operation, maintenance and capital expenditures of Springerville Unit 3 and the decisions related to those expenditures including budgeting, financing and dispatch of power. Based on all these facts, it was determined that we are the primary beneficiary of the Owner Lessor. Therefore, the Springerville Partnership and Owner Lessor have been consolidated by us. Assets and liabilities of the Springerville Partnership that are included in our consolidated statements of financial position are as follows (dollars in thousands): September 30, December 31, 2020 2019 Net electric plant $ 762,808 $ 776,411 Noncontrolling interest 113,425 111,717 Long-term debt 342,680 380,867 Accrued interest 3,977 11,050 Our consolidated statements of operations include the following Springerville Partnership expenses for the three and nine months ended September 30, 2020 and 2019 (dollars in thousands): September 30, September 30, 2020 2019 2020 2019 Depreciation, amortization and depletion $ 4,535 $ 4,535 $ 13,603 $ 13,603 Interest 5,646 6,281 $ 17,157 19,045 The revenue associated with the Springerville Partnership lease has been eliminated in consolidation. Income, losses and cash flows of the Springerville Partnership are allocated to the general and limited partners based on their equity ownership percentages. The net income or loss attributable to the 49 percent noncontrolling equity interest in the Springerville Partnership is reflected on our consolidated statements of operations. Unconsolidated Variable Interest Entities Western Fuels Association, Inc. (“WFA”) : WFA is a non-profit membership corporation organized for the purpose of acquiring and supplying fuel resources to its members, which includes us. WFA, through its ownership in Western Fuels-Wyoming, supplies fuel to MBPP for the use at the Laramie River Station. We also received coal supplies directly from WFA for the Escalante Generating Station in New Mexico. The pricing structure of the coal supply agreements with WFA is designed to recover the mine operating costs of the mine supplying the coal and therefore the coal sales agreements provide the financial support for the mine operations. There is not sufficient equity at risk for WFA to finance its activities without additional financial support. Therefore, WFA is considered a variable interest entity in which we have a variable interest. The power to direct the activities that most significantly impact WFA’s economic performance (acquiring and supplying fuel resources) is held by the members who are represented on the WFA board of directors whose actions require joint approval. Therefore, since there is shared power over the significant activities of WFA, we are not the primary beneficiary of WFA and the entity is not consolidated. Our investment in WFA, accounted for using the cost method, was $2.3 million at September 30, 2020 and $2.4 million at December 31, 2019 and is included in investments in other associations. Western Fuels – Wyoming (“WFW”) : WFW, the owner and operator of the Dry Fork Mine in Gillette, Wyoming, was organized for the purpose of acquiring and supplying coal, through long-term coal supply agreements, to be used in the production of electric energy at the Laramie River Station (owned by the participants of MBPP) and at the Dry Fork Station (owned by Basin). WFA owns 100 percent of the class AA shares and 75 percent of the class BB shares of WFW, while the participants of MBPP (of which we have a 27.13 percent undivided interest) own the remaining 25 percent of class BB shares of WFW. The pricing structure of the coal supply agreements is designed to recover the costs of production of the Dry Fork Mine and therefore the coal supply agreements provide the financial support for the operation of the Dry Fork Mine. There is not sufficient equity at risk at WFW for it to finance its activities without additional financial support. Therefore, WFW is considered a variable interest entity in which we have a variable interest. The power to direct the activities that most significantly impact WFW’s economic performance (which includes operations, maintenance and reclamation activities) is shared with the equity interest holders since each member has representation on the WFW board of directors whose actions require joint approval. Therefore, we are not the primary beneficiary of WFW and the entity is not consolidated. Our investment in WFW, accounted for using the cost method, was $0.1 million at September 30, 2020 and December 31, 2019 and is included in investments in other associations. Trapper Mining, Inc. (“Trapper Mining”) : Trapper Mining is a cooperative organized for the purpose of mining, selling and delivering coal from the Trapper Mine to the Craig Generating Station Units 1 and 2 through long-term coal supply agreements. Trapper Mining is jointly owned by some of the participants of the Yampa Project. We have a 26.57 percent cooperative member interest in Trapper Mining. The pricing structure of the coal supply agreements is designed to recover the costs of production of the Trapper Mine and therefore the coal supply agreements provide the financial support for the operation of the Trapper Mine. There is not sufficient equity at risk for Trapper Mining to finance its activities without the additional financial support. Therefore, Trapper Mining is considered a variable interest entity in which we have a variable interest. The power to direct the activities that most significantly impact Trapper Mining’s economic performance (which includes operations, maintenance and reclamation activities) is shared with the members since each member has representation on the Trapper Mining board of directors whose actions require joint approval. Therefore, we are not the primary beneficiary of Trapper Mining and the entity is not consolidated. We record our investment in Trapper Mining using the equity method. Our membership interest in Trapper Mining was $16.3 million at September 30, 2020 and $15.9 million at December 31, 2019.

LEGAL

LEGAL	9 Months Ended
	Sep. 30, 2020
LEGAL
LEGAL	NOTE 18 – LEGAL Other than as disclosed below, we do not expect any litigation or proceeding pending or threatened against us to have a potential material effect on our financial condition, results of operations or cash flows. Transmission Agreement: Pursuant to a long-term transmission agreement with another utility, such utility pays for and has firm rights to transfer power and energy across a transmission path in Colorado. Such right to payment and obligation to provide the transfer is borne equally by us and another entity. Due to the current capacity of the transmission path, such utility’s firm rights have been curtailed. The utility disputes its obligation to pay due to the current capacity of the transmission path and claims we, along with the other entity, are in breach of such transmission agreement. The utility notified us and the other entity of its intent to arbitrate in accordance with the agreement and claimed damages caused by the alleged breach of approximately $6.9 million, plus interest, attorney fees, and any future damages. The other entity filed a cross-claim against us claiming we are responsible for such entity’s share of any damages. The matter was scheduled for arbitration to commence in January 2020. The arbitration was suspended and the parties have reached a resolution of this matter without us incurring any liability. The resolution of this matter is subject to FERC approval. On October 20, 2020, an unexecuted version of an amended and restated transmission agreement to resolve this matter was filed with FERC for approval. It is not possible to predict if FERC will approve this agreement. FERC Tariff and Declaratory Order: At our July 2019 Board meeting, our Board authorized us to take action to place us under wholesale rate regulation by FERC. On September 3, 2019, a membership agreement with a Non-Utility Member, MIECO, Inc., became effective. The admission of the new Non-Utility Member that was not an electric cooperative or governmental entity resulted in us no longer being exempt from FERC wholesale rate regulation pursuant to the Federal Power Act (“FPA”). In December 2019, we filed our tariff filings, including our stated rate cost of service filing, market based rate authorization, and transmission Open Access Transmission Tariff. The request was made to FERC to make the new tariffs retroactive to September 3, 2019. In addition, on December 23, 2019, we filed our Petition for Declaratory Order (“PDO”) with FERC asking FERC to confirm our jurisdiction under the FPA and that FERC’s jurisdiction preempts the jurisdiction of the Colorado Public Utilities Commission (“COPUC”) to address any rate related issues. On March 20, 2020, FERC issued orders regarding our PDO and our tariff filings. FERC’s orders generally accepted our tariff filings and recognized that we became FERC jurisdictional on September 3, 2019, but did not make the tariffs retroactive to September 3, 2019. However, FERC specifically provided that no refunds are due on our Utility Member rates and our transmission service rates prior to March 26, 2020. FERC did not impose any civil penalties on us. FERC also did not determine that our Utility Member rates and transmission service rates were just and reasonable and ordered a 206 proceeding to determine the justness and reasonableness of our rates and wholesale electric service contracts. FERC also rejected our Board Policy 115 (“BP 115”) and member project contracts related our Utility Member’s election to provide up to 5 percent of its electric power requirements pursuant to their wholesale electric service contracts on the grounds that the initial filing was incomplete without Board Policy 101 (“BP 101”) related to the self-supply in excess of the 5 percent annual allowance. The tariff rates were referred to an administrative law judge to encourage settlement of material issues and to hold a hearing if settlement is not reached. The settlement proceedings are continuing and settlement offers are being exchanged under the FERC administrative law judge’s guidance and in participation with FERC staff. Any refunds to the applicable tariff rates would only apply to after March 26, 2020. FERC’s March 20, 2020 order regarding our PDO denied our requested declaration regarding the preemption of two of our Utility Members proceedings at the COPUC stating they are not currently preempted. On April 13, 2020, we filed a request for rehearing limited to the issue of preemption of the COPUC related to the contract termination payment amount as described in our PDO. Requests for rehearing related to both the PDO and tariff filings were filed with FERC by other parties. On August 28, 2020, FERC issued an order on rehearing related to our PDO which modified its March 20, 2020 decision by finding exclusive jurisdiction over our contract termination payments and preempting the jurisdiction of the COPUC as of September 3, 2019 (“August 28 Order”). The August 28 Order also set aside requests for rehearing filed with FERC by other parties related to the PDO. Requests for rehearing related to FERC’s August 28 Order were filed with FERC by two of our Utility Members. On October 28, 2020, FERC issued an order denying the requests for rehearing filed by two of our Utility Members. On July 1, 2020, we re-submitted our BP 101, BP 115, and all existing member project contracts with FERC for acceptance and on August 28, 2020 FERC accepted the filings effective August 31, 2020. FERC also ordered a 206 proceeding to determine whether our July 1 filed documents are just and reasonable and set them for settlement and hearing procedures, which were consolidated with the ongoing settlement and hearing procedures in effect for our member rates docket. FERC also established a refund effective date related to our July 1 filed documents of September 1, 2020. Requests for rehearing related to this FERC order has been filed with FERC by one of our Utility Members. On July 13, 2020, we filed a petition for review with the United States Court of Appeals for the District of Columbia Circuit (“D.C. Circuit Court of Appeals”) to protect our interest, and requested review of FERC’s order granting in part and denying in part our PDO and FERC’s order granting rehearings for further consideration. Petitions for review related to both the PDO and tariff filings have been filed with the D.C. Circuit Court of Appeals by other parties. On September 18, 2020, FERC filed to hold the appeals in abeyance. On September 29, 2020, an order was filed considering the motion to hold the case in abeyance, directing the parties to file motions to govern future proceedings by January 11, 2021. It is not possible to predict if FERC will require us to refund amounts to our customers for sales after March 26, 2020, if FERC will approve our current practices regarding use of regulatory assets are just and reasonable, or to estimate any liability associated with these matters. In addition, we cannot predict the outcome of the 206 proceedings, any requests for rehearing filed with FERC, or our petition for review or any other petitions for review filed with the D.C. Circuit Court of Appeals. United Adams District Court Complaint: On May 4, 2020, United Power, Inc. (“United”) filed a Complaint for Declaratory Judgement and Damages in the Adams County District Court against us and our three Non-Utility Members alleging, among other things, that the April 2019 Bylaws amendment that allows our Board to establish one or more classes of membership in addition to the then existing all-requirements class of membership is void, the April 2020 Board approvals related to a “Make-Whole” methodology for a contract termination payment and buy-down payment formula are also void, that we have breached the wholesale electric service contract with United, and that we and our three Non-Utility Members conspired to deprive the COPUC of jurisdiction over the contract termination payment of our Colorado Utility Members. On June 20, 2020, we filed our answer denying United’s allegations and request for relief, and asked the court to dismiss United’s claims. We asserted counterclaims against United, and are seeking relief from United’s breach of our Bylaws and declaratory judgement that the April 2019 Bylaws amendment and the April 2020 Board approvals related to a “Make-Whole” methodology for a contract termination payment and buy-down payment formula are valid. On June 20, 2020, the three Non-Utility Members filed a joint motion to dismiss. United filed its response on July 30, 2020. It is not possible to predict the outcome of this matter or whether we will incur any liability in connection with this matter.

PRESENTATION OF FINANCIAL INF_2

PRESENTATION OF FINANCIAL INFORMATION (Tables)	9 Months Ended
	Sep. 30, 2020
PRESENTATION OF FINANCIAL INFORMATION
Schedule of jointly owned facilities	Our share in each jointly owned facility is as follows as of September 30, 2020 (dollars in thousands): Electric Construction Tri-State Plant in Accumulated Work In Share Service Depreciation Progress Yampa Project - Craig Generating Station Units 1 and 2 24.00 % $ 395,099 $ 249,804 $ 334 MBPP - Laramie River Station 27.13 % 489,147 301,561 5,075 Total $ 884,246 $ 551,365 $ 5,409

ACCOUNTING FOR RATE REGULATION

ACCOUNTING FOR RATE REGULATION (Tables)	9 Months Ended
	Sep. 30, 2020
ACCOUNTING FOR RATE REGULATION
Schedule of regulatory assets and liabilities	Regulatory assets and liabilities are as follows (dollars in thousands): September 30, December 31, 2020 2019 Regulatory assets Deferred income tax expense (1) $ 33,744 $ 58,937 Deferred prepaid lease expense – Springerville Unit 3 Lease (2) 81,996 83,714 Goodwill – J.M. Shafer (3) 47,008 49,145 Goodwill – Colowyo Coal (4) 36,419 37,194 Deferred debt prepayment transaction costs (5) 134,459 140,931 Deferred Holcomb expansion impairment loss (6) 89,988 93,494 Unrecovered plant (7) 293,563 33,864 Total regulatory assets 717,177 497,279 Regulatory liabilities Interest rate swap - realized gain (8) 3,391 3,744 Deferred revenues (9) 75,853 75,853 Membership withdrawal (10) 157,943 42,572 Total regulatory liabilities 237,187 122,169 Net regulatory asset $ 479,990 $ 375,110 (1) A regulatory asset or liability associated with deferred income taxes generally represents the future increase or decrease in income taxes payable that will be received or settled through future rate revenues. (2) Represents deferral of the loss on acquisition related to the Springerville Generating Station Unit 3 (“Springerville Unit 3”) prepaid lease expense upon acquiring a controlling interest in the Springerville Unit 3 Partnership LP (“Springerville Partnership”) in 2009. The regulatory asset for the deferred prepaid lease expense is being amortized to depreciation, amortization and depletion expense in the amount of $2.3 million annually through the 47-year period ending in 2056 and recovered from our Utility Members through rates. (3) Represents goodwill related to our acquisition of Thermo Cogeneration Partnership, LP in December 2011. Goodwill is being amortized to depreciation, amortization and depletion expense in the amount of $2.8 million annually through the 25-year period ending in 2036 and recovered from our Utility Members through rates. (4) Represents goodwill related to our acquisition of Colowyo Coal Company LP (“Colowyo Coal”) in December 2011. Goodwill is being amortized to depreciation, amortization and depletion expense in the amount of $1.0 million annually through the 44-year period ending in 2056 and recovered from our Utility Members through rates. (5) Represents transaction costs that we incurred related to the prepayment of our long-term debt in 2014. These costs are being amortized to depreciation, amortization and depletion expense in the amount of $8.6 million annually over the 21.4-year period ending in 2036 and recovered from our Utility Members through rates. (6) Represents deferral of the impairment loss related to development costs, including costs for the option to purchase development rights for the expansion of the Holcomb Generating Station. Beginning January 2020, the deferred impairment loss is being amortized to depreciation, amortization and depletion expense in the amount of $4.7 million annually over the 20-year period ending in 2039 and recovered from our Utility Members through rates. (7) Represents deferral of the impairment losses related to the early retirement of the Nucla and Escalante Generating Stations. In July 2019, our Board took action for the early retirement of the Nucla Generating Station and the deferral of any impairment loss in accordance with accounting for rate regulation. In conjunction with the early retirement of the Nucla Generating Station, we recognized an impairment loss of $37.1 million during the third quarter of 2019. On September 19, 2019, the Nucla Generating Station was officially retired from service. The deferred impairment loss for Nucla Generating Station is being amortized to depreciation, amortization and depletion expense over the 3.3-year period ending in December 2022 and recovered from our Utility Members through rates. In January 2020, our Board approved the early retirement of the Escalante Generating Station and the deferral of any impairment loss in accordance with accounting for rate regulation. In conjunction with the early retirement, we recognized an impairment loss of $268.2 million during the first quarter of 2020. The deferred impairment loss for Escalante Generating Station will be amortized to depreciation, amortization and depletion expense beginning in 2021 through the end of 2045, which was the depreciable life of Escalante Generating Station, and is expected to be recovered from our Utility Members through rates. The annual amortization is expected to approximate the former annual Escalante Generating Station depreciation for the remaining life of the asset. (8) Represents deferral of a realized gain of $4.6 million related to the October 2017 settlement of a forward starting interest rate swap. This realized gain was deferred as a regulatory liability and is being amortized to interest expense over the 12-year term of the First Mortgage Obligations, Series 2017A and refunded to Utility Members through reduced rates when recognized in future periods. (9) Represents deferral of the recognition of non-member electric sales revenues. These deferred non-member electric sales revenues will be refunded to Utility Members through reduced rates when recognized in non-member electric sales revenue in future periods. Represents the deferral of the recognition of other income related to the June 30, 2016 withdrawal of a former Utility Member from membership in us and the June 30, 2020 withdrawal of Delta-Montrose Electric Association (“DMEA”) from membership in us. In connection with the DMEA withdrawal, we recognized $110.2 million of other income and $5.2 million of gain on sale of assets which was subsequently deferred. The total deferred membership withdrawal income will be refunded to Utility Members through reduced rates, subject to FERC approval, when recognized in other income in future periods.

INVESTMENTS IN OTHER ASSOCIAT_2

INVESTMENTS IN OTHER ASSOCIATIONS (Tables)	9 Months Ended
	Sep. 30, 2020
INVESTMENTS IN OTHER ASSOCIATIONS
Schedule of investments in other associations	Investments in other associations are as follows (dollars in thousands): September 30, December 31, 2020 2019 Basin Electric Power Cooperative $ 114,036 $ 117,368 National Rural Utilities Cooperative Finance Corporation - patronage capital 11,933 11,761 National Rural Utilities Cooperative Finance Corporation - capital term certificates 15,885 15,953 CoBank, ACB 11,141 10,201 Western Fuels Association, Inc. 2,302 2,409 Other 3,890 4,253 Investments in other associations $ 159,187 $ 161,945

INVESTMENTS IN AND ADVANCES T_2

INVESTMENTS IN AND ADVANCES TO COAL MINES (Tables)	9 Months Ended
	Sep. 30, 2020
INVESTMENTS IN AND ADVANCES TO COAL MINES
Schedule of investments in and advances to coal mines	Investments in and advances to coal mines are as follows (dollars in thousands): September 30, December 31, 2020 2019 Investment in Trapper Mine $ 16,279 $ 15,881 Advances to Dry Fork Mine 3,279 3,800 Investments in and advances to coal mines $ 19,558 $ 19,681

CASH, CASH EQUIVALENTS AND RE_2

CASH, CASH EQUIVALENTS AND RESTRICTED CASH AND INVESTMENTS (Tables)	9 Months Ended
	Sep. 30, 2020
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents [Abstract]
Schedule of cash, cash equivalents and restricted cash and investments	The following table provides a reconciliation of cash, cash equivalents and restricted cash and investments reported within our consolidated statements of financial position that sum to the total of the same such amount shown in our consolidated statements of cash flows (dollars in thousands): September 30, December 31, 2020 2019 Cash and cash equivalents $ 164,965 $ 83,070 Restricted cash and investments - current 199 182 Restricted cash and investments - noncurrent 4,887 30,516 Cash, cash equivalents and restricted cash and investments $ 170,051 $ 113,768

CONTRACT ASSETS AND CONTRACT _2

CONTRACT ASSETS AND CONTRACT LIABILITIES (Tables)	9 Months Ended
	Sep. 30, 2020
CONTRACT ASSETS AND CONTRACT LIABILITIES
Schedule of contract assets and liabilities	September 30, December 31, 2020 2019 Accounts receivable - Utility Members $ 99,420 $ 105,371 Other accounts receivable - trade: Non-member electric sales 7,900 4,727 Other 16,615 20,628 Total other accounts receivable - trade 24,515 25,355 Other accounts receivable - nontrade 683 2,684 Total other accounts receivable $ 25,198 $ 28,039 Contract liabilities (unearned revenue) $ 6,281 $ 7,041

OTHER DEFERRED CHARGES (Tables)

OTHER DEFERRED CHARGES (Tables)	9 Months Ended
	Sep. 30, 2020
OTHER DEFERRED CHARGES.
Schedule of Other Deferred Charges	The following other deferred charges are reflected on our consolidated statements of financial position (dollars in thousands): September 30, December 31, 2020 2019 Preliminary surveys and investigations $ 23,012 $ 21,261 Advances to operating agents of jointly owned facilities 8,686 3,917 Operating lease right-of-use assets 10,086 7,622 Other 16,886 9,872 Total other deferred charges $ 58,670 $ 42,672

LONG-TERM DEBT (Tables)

LONG-TERM DEBT (Tables)	9 Months Ended
	Sep. 30, 2020
LONG-TERM DEBT.
Schedule of long-term debt	Long-term debt consists of the following (dollars in thousands): September 30, December 31, 2020 2019 Total debt $ 3,314,353 3,166,472 Less debt issuance costs (26,218) (27,412) Less debt discounts (9,722) (9,906) Plus debt premiums 14,669 15,752 Total debt adjusted for debt issuance costs, discounts and premiums 3,293,082 3,144,906 Less current maturities (87,178) (81,555) Long-term debt $ 3,205,904 $ 3,063,351

SHORT-TERM BORROWINGS (Tables)

SHORT-TERM BORROWINGS (Tables)	9 Months Ended
	Sep. 30, 2020
SHORT-TERM BORROWINGS
Schedule of commercial paper	Commercial paper consisted of the following (dollars in thousands): September 30, December 31, 2020 2019 Commercial paper outstanding, net of discounts $ — $ 252,323 Weighted average interest rate — % 1.88 %

ASSET RETIREMENT OBLIGATIONS (T

ASSET RETIREMENT OBLIGATIONS (Tables)	9 Months Ended
	Sep. 30, 2020
ASSET RETIREMENT OBLIGATION
Schedule of Asset Retirement Obligations	Aggregate carrying amounts of asset retirement obligations and environmental reclamation obligations are as follows (dollars in thousands): Nine Months Ended September 30, 2020 Obligations at beginning of period $ 78,914 Liabilities incurred — Liabilities settled (824) Accretion expense 1,895 Change in cash flow estimate 3,158 Total obligations at end of period $ 83,143 Less current obligations at end of period (2,840) Long-term obligations at end of period $ 80,303

OTHER DEFERRED CREDITS AND OT_2

OTHER DEFERRED CREDITS AND OTHER LIABILITIES (Tables)	9 Months Ended
	Sep. 30, 2020
OTHER DEFERRED CREDITS AND OTHER LIABILITIES
Schedule of other deferred credits and other liabilities	The following other deferred credits and other liabilities are reflected on our consolidated statements of financial position (dollars in thousands): September 30, December 31, 2020 2019 Transmission easements $ 20,148 $ 20,549 Operating lease liabilities - noncurrent 1,705 1,846 Contract liabilities (unearned revenue) - noncurrent 3,781 4,217 Customer deposits 7,404 3,015 Financial liabilities - reclamation 10,217 12,091 Other 13,222 14,681 Total other deferred credits and other liabilities $ 56,477 $ 56,399

EMPLOYEE BENEFIT PLANS (Tables)

EMPLOYEE BENEFIT PLANS (Tables)	9 Months Ended
	Sep. 30, 2020
Postretirement Medical Benefit Plans
Schedule of employee benefit plan obligations	The postretirement medical benefit and postemployment medical benefit obligations are determined annually (during the fourth quarter) by an independent actuary and are included in accumulated postretirement benefit and postemployment obligations on our consolidated statements of financial position as follows (dollars in thousands): Nine Months Ended September 30, 2020 Postretirement medical benefit obligation at beginning of period $ 10,195 Service cost 422 Interest cost 264 Benefit payments (net of contributions by participants) (465) Postretirement medical benefit obligation at end of period $ 10,416 Postemployment medical benefit obligation at end of period 375 Total postretirement and postemployment medical obligations at end of period $ 10,791
Schedule of the net unrecognized actuarial gains and losses related to employee benefit plan obligations	The net unrecognized actuarial gains and losses related to the postretirement medical benefit obligations are included in accumulated other comprehensive income as follows (dollars in thousands): Nine Months Ended September 30, 2020 Accumulated other comprehensive loss at beginning of period $ (1,387) Amortization of actuarial (gain) loss into income 11 Amortization of prior service credit into other income (59) Accumulated other comprehensive loss at end of period $ (1,435)
NRECA Executive Benefit Restoration Plan
Schedule of employee benefit plan obligations	The NRECA Executive Benefit Restoration Plan obligations are determined annually (during the first quarter of the subsequent year) by an NRECA actuary and are included in accumulated postretirement benefit and postemployment obligations on our consolidated statements of financial position as follows (dollars in thousands): Nine Months Ended September 30, 2020 Executive benefit restoration obligation at beginning of period $ 674 Service cost 312 Interest cost 417 Plan amendments - prior service cost 5,218 Benefit payments (715) Actuarial loss 2,155 Executive benefit restoration at end of period $ 8,061
Schedule of the net unrecognized actuarial gains and losses related to employee benefit plan obligations	The net unrecognized actuarial gains and losses related to the executive benefit restoration obligations are included in accumulated other comprehensive income as follows (dollars in thousands): Nine Months Ended September 30, 2020 Accumulated other comprehensive loss at beginning of period $ (130) Plan amendments - prior service cost (5,218) Amortization of prior service cost into other income 1,336 Unrecognized actuarial loss (2,155) Accumulated other comprehensive loss at end of period $ (6,167)

REVENUE (Tables)

REVENUE (Tables)	9 Months Ended
	Sep. 30, 2020
REVENUE
Schedule of revenue from contracts with non-member customers and other operating revenue	The following revenue is reflected on our consolidated statements of operations as follows (dollars in thousands): Three Months Ended September 30, Nine Months Ended September 30, 2020 2019 2020 2019 Non-member electric sales: Long-term contracts $ 9,423 $ 12,647 $ 32,817 $ 35,241 Short-term contracts 29,183 15,692 38,227 36,602 Other 16,226 12,128 37,150 39,540 Total non-member electric sales and other operating revenue $ 54,832 $ 40,467 $ 108,194 $ 111,383

LEASES (Tables)

LEASES (Tables)	9 Months Ended
	Sep. 30, 2020
LEASES
Schedule of lease components	Our consolidated statements of financial position include the following lease components (dollars in thousands): September 30, December 31, 2020 2019 Operating leases Operating lease right-of-use assets $ 11,464 $ 8,376 Less: Accumulated amortization (1,378) (754) Net operating lease right-of-use assets $ 10,086 $ 7,622 Operating lease liabilities - current $ (556) $ (5,533) Operating lease liabilities - noncurrent (1,705) (1,846) Total operating lease liabilities $ (2,261) $ (7,379) Operating leases Weighted average remaining lease term (years) Weighted average discount rate
Schedule of expected minimum lease commitments under operating leases	Future expected minimum lease commitments under operating leases are as follows (dollars in thousands): Year 1 $ 609 Year 2 444 Year 3 341 Year 4 315 Year 5 196 Thereafter 737 Total lease payments $ 2,642 Less imputed interest (381) Total $ 2,261

FAIR VALUE (Tables)

FAIR VALUE (Tables)	9 Months Ended
	Sep. 30, 2020
Marketable securities
FAIR VALUE
Schedule of carrying amounts and fair values of assets and liabilities	The cost and fair values of our marketable securities are as follows (dollars in thousands): September 30, 2020 December 31, 2019 Estimated Estimated Cost Fair Value Cost Fair Value Marketable securities $ 477 $ 429 $ 715 $ 654
Debt
FAIR VALUE
Schedule of carrying amounts and fair values of assets and liabilities	The principal amounts and fair values of our debt are as follows (dollars in thousands): September 30, 2020 December 31, 2019 Principal Estimated Principal Estimated Amount Fair Value Amount Fair Value Total debt $ 3,314,353 $ 3,926,312 $ 3,166,472 $ 3,608,341

VARIABLE INTEREST ENTITIES (Tab

VARIABLE INTEREST ENTITIES (Tables)	9 Months Ended
	Sep. 30, 2020
VARIABLE INTEREST ENTITIES
Schedule of consolidated variable interest entities	Assets and liabilities of the Springerville Partnership that are included in our consolidated statements of financial position are as follows (dollars in thousands): September 30, December 31, 2020 2019 Net electric plant $ 762,808 $ 776,411 Noncontrolling interest 113,425 111,717 Long-term debt 342,680 380,867 Accrued interest 3,977 11,050 Our consolidated statements of operations include the following Springerville Partnership expenses for the three and nine months ended September 30, 2020 and 2019 (dollars in thousands): September 30, September 30, 2020 2019 2020 2019 Depreciation, amortization and depletion $ 4,535 $ 4,535 $ 13,603 $ 13,603 Interest 5,646 6,281 $ 17,157 19,045

PRESENTATION OF FINANCIAL INF_3

PRESENTATION OF FINANCIAL INFORMATION (Details) $ in Thousands	9 Months Ended
	Sep. 30, 2020USD ($)itemclassfacility
Jointly owned facilities
Number of jointly owned facilities | facility	2
Electric plant in service	$ 884,246
Accumulated depreciation	551,365
Construction work in progress	$ 5,409
Member information
Number of classes of members | class	3
Yampa
Jointly owned facilities
Tri-State share (as a percent)	24.00%
Electric plant in service	$ 395,099
Accumulated depreciation	249,804
Construction work in progress	$ 334
MBPP
Jointly owned facilities
Tri-State share (as a percent)	27.13%
Electric plant in service	$ 489,147
Accumulated depreciation	301,561
Construction work in progress	$ 5,075
Class A Members
Member information
Number of members | item	42
Class B Members
Member information
Number of members | item	0
Non-Utility Members
Member information
Number of members | item	3

PRESENTATION OF FINANCIAL INF_4

PRESENTATION OF FINANCIAL INFORMATION - Membership Withdrawal (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Sep. 30, 2020	Dec. 31, 2019
Membership withdrawal
Regulatory Liabilities		$ 237,187	$ 122,169
DMEA
Membership withdrawal
Gain on sale of electric plant	$ 5,200

ACCOUNTING FOR RATE REGULATIO_2

ACCOUNTING FOR RATE REGULATION (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Oct. 31, 2017	Mar. 31, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Regulatory assets and liabilities
Regulatory assets					$ 717,177		$ 497,279
Regulatory liabilities					237,187		122,169
Net regulatory asset					479,990		375,110
Impairment loss					259,761	$ 37,067
Interest rate swaps, realized gain
Regulatory assets and liabilities
Regulatory liabilities					3,391		3,744
Proceeds from settlement of interest rate swaps		$ 4,600
Deferred non-member electric sales
Regulatory assets and liabilities
Regulatory liabilities					75,853		75,853
Deferred revenue from membership withdrawal
Regulatory assets and liabilities
Regulatory liabilities					$ 157,943		42,572
First Mortgage Obligations, Series 2017A , Tranche 1, 3.34%, due through 2029
Regulatory assets and liabilities
Term of issuance					12 years
Deferred income tax expense
Regulatory assets and liabilities
Regulatory assets					$ 33,744		58,937
Deferred prepaid lease expense | Springerville Unit 3 Lease
Regulatory assets and liabilities
Regulatory assets					81,996		83,714
Annual amortization expense					$ 2,300
Amortization period					47 years
Goodwill | TCP
Regulatory assets and liabilities
Regulatory assets					$ 47,008		49,145
Annual amortization expense					$ 2,800
Amortization period					25 years
Goodwill | Colowyo Coal
Regulatory assets and liabilities
Regulatory assets					$ 36,419		37,194
Annual amortization expense					$ 1,000
Amortization period					44 years
Deferred debt prepayment transaction costs
Regulatory assets and liabilities
Regulatory assets					$ 134,459		140,931
Annual amortization expense					$ 8,600
Amortization period					21 years 4 months 24 days
Deferred impairment loss | Unrecovered Plants
Regulatory assets and liabilities
Regulatory assets					$ 293,563		33,864
Deferred impairment loss | Nucla Generating Station
Regulatory assets and liabilities
Impairment loss				$ 37,100
Amortization period					3 years 3 months 18 days
Deferred impairment loss | Escalante Generating Station
Regulatory assets and liabilities
Impairment loss			$ 268,200
Deferred impairment loss | Holcomb Expansion
Regulatory assets and liabilities
Regulatory assets					$ 89,988		$ 93,494
Annual amortization expense					$ 4,700
Amortization period					20 years
DMEA
Regulatory assets and liabilities
Gain on sale of electric plant	$ 5,200
DMEA | Deferred revenue from membership withdrawal
Regulatory assets and liabilities
Regulatory liabilities	$ 110,200

INVESTMENTS IN OTHER ASSOCIAT_3

INVESTMENTS IN OTHER ASSOCIATIONS (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2020	Dec. 31, 2019
Investment in other associations
Investment in other associations	$ 159,187	$ 161,945
Impairment during the period	0	0
Basin Electric Power Cooperative
Investment in other associations
Investment in other associations	114,036	117,368
National Rural Utilities Cooperative Finance Corporation - patronage capital
Investment in other associations
Investment in other associations	11,933	11,761
National Rural Utilities Cooperative Finance Corporation - capital term certificates
Investment in other associations
Investment in other associations	15,885	15,953
CoBank, ACB
Investment in other associations
Investment in other associations	11,141	10,201
Western Fuels Association
Investment in other associations
Investment in other associations	2,302	2,409
Other
Investment in other associations
Investment in other associations	$ 3,890	$ 4,253

INVESTMENTS IN AND ADVANCES T_3

INVESTMENTS IN AND ADVANCES TO COAL MINES (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Investments in and advances to coal mines
Investments in and advances to coal mines	$ 19,558	$ 19,681
Trapper Mining
Investments in and advances to coal mines
Investment in coal mine	16,279	15,881
Dry Fork Mine
Investments in and advances to coal mines
Advances	$ 3,279	$ 3,800

CASH, CASH EQUIVALENTS AND RE_3

CASH, CASH EQUIVALENTS AND RESTRICTED CASH AND INVESTMENTS (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Mar. 10, 2020	Dec. 31, 2019	Sep. 30, 2019	Dec. 31, 2018
Cash, cash equivalents, restricted cash and investments
Cash and cash equivalents	$ 164,965		$ 83,070
Restricted cash and investments - current	199		182
Restricted cash and investments - noncurrent	4,887		30,516
Cash, cash equivalents and restricted cash and investments	$ 170,051		113,768	$ 120,431	$ 127,590
Internally restricted cash			$ 25,500
Internally restricted cash released		$ 25,500

CONTRACT ASSETS AND CONTRACT _3

CONTRACT ASSETS AND CONTRACT LIABILITIES (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2020	Dec. 31, 2019
Accounts receivable
Accounts receivable—Utility Members	$ 99,420	$ 105,371
Other accounts receivable	25,198	28,039
Contract liabilities
Contract liabilities (unearned revenue)	6,281	7,041
Other accounts receivable - trade
Accounts receivable
Other accounts receivable	24,515	25,355
Other accounts receivable - trade | Non-member electric sales
Accounts receivable
Other accounts receivable	7,900	4,727
Other accounts receivable - trade | Other
Accounts receivable
Other accounts receivable	16,615	20,628
Other accounts receivable, non-trade
Accounts receivable
Other accounts receivable	683	$ 2,684
Other operating revenue
Contract liabilities
Contract liabilities recognized	$ 900

OTHER DEFERRED CHARGES (Details

OTHER DEFERRED CHARGES (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
OTHER DEFERRED CHARGES.
Preliminary surveys and investigations	$ 23,012	$ 21,261
Advances to operating agents of jointly owned facilities	8,686	3,917
Operating lease right-of-use assets	10,086	7,622
Other	16,886	9,872
Total other deferred charges	$ 58,670	$ 42,672

LONG-TERM DEBT - Other Informat

LONG-TERM DEBT - Other Information (Details)	9 Months Ended
	Sep. 30, 2020USD ($)	Sep. 30, 2019USD ($)	Dec. 31, 2019USD ($)
Debt
Long-term debt	$ 3,205,904,000		$ 3,063,351,000
Unsecured debt
Number of unsecured debt instruments	1
Unsecured notes	$ 21,500,000
Credit facility information
Outstanding borrowings	3,314,353,000		$ 3,166,472,000
Proceeds from debt draw	$ 425,000,000	$ 34,910,000
Minimum
Credit facility information
Equity to capitalization ratio (ECR) requirement	18.00%
Debt service ratio (DSR) requirement	1.10
Springerville certificates, Series B, 7.14%, due through 2033
Credit facility information
Debt service ratio (DSR) requirement	1.02
2018 Revolving Credit Agreement
Credit facility information
Maximum borrowing capacity	$ 650,000,000
Available borrowing capacity	650,000,000
2018 Revolving Credit Agreement | Commercial Paper
Credit facility information
Available borrowing capacity	500,000,000
Swingline
Credit facility information
Maximum borrowing capacity	100,000,000
Letter of Credit
Credit facility information
Maximum borrowing capacity	75,000,000
Commercial Paper
Credit facility information
Maximum borrowing capacity	$ 500,000,000

LONG-TERM DEBT - Components (De

LONG-TERM DEBT - Components (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Long-term debt, components
Total debt	$ 3,314,353	$ 3,166,472
Less debt issuance costs	(26,218)	(27,412)
Less debt discounts	(9,722)	(9,906)
Plus debt premiums	14,669	15,752
Total debt adjusted for debt issuance costs, discounts and premiums	3,293,082	3,144,906
Less current maturities	(87,178)	(81,555)
Long-term debt	$ 3,205,904	$ 3,063,351

SHORT-TERM BORROWINGS (Details)

SHORT-TERM BORROWINGS (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2020	Dec. 31, 2019
Short-term borrowings
Amount outstanding		$ 252,323
Commercial Paper
Short-term borrowings
Amount outstanding		$ 252,323
Weighted average interest rate		1.88%
Commercial Paper | Maximum
Short-term borrowings
Maximum amount per commercial paper sublimit	$ 500,000
Term of issuance	397 days
2018 Revolving Credit Agreement
Short-term borrowings
Available borrowing capacity	$ 650,000
2018 Revolving Credit Agreement | Commercial Paper
Short-term borrowings
Available borrowing capacity	$ 500,000

ASSET RETIREMENT OBLIGATIONS (D

ASSET RETIREMENT OBLIGATIONS (Details) $ in Thousands	9 Months Ended
	Sep. 30, 2020USD ($)item	Dec. 31, 2019USD ($)
Aggregate carrying amounts of asset retirement obligations
Asset retirement obligation at beginning of period	$ 78,914
Liabilities settled	(824)
Accretion expense	1,895
Change in cash flow estimate	3,158
Asset retirement obligation at end of period	83,143
Less current asset retirement obligations	(2,840)	$ (2,460)
Long-term obligations at end of period	$ 80,303
Colowyo Mine
Aggregate carrying amounts of asset retirement obligations
Number of mine pits in final reclamation | item	1

OTHER DEFERRED CREDITS AND OT_3

OTHER DEFERRED CREDITS AND OTHER LIABILITIES (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2020	Dec. 31, 2019
Deferred credits and other liabilities
Transmission easements	$ 20,148	$ 20,549
Operating lease liabilities - noncurrent	1,705	1,846
Contract liabilities (unearned revenue) - noncurrent	3,781	4,217
Customer deposits	7,404	3,015
Financial liabilities - reclamation	10,217	12,091
Other	13,222	14,681
Total other deferred credits and other liabilities	56,477	56,399
Transmission Right of Way Easements
Deferred credits and other liabilities
Total due for easement right of way	31,200
Other Deferred Credits and Other Liabilities | Transmission Right of Way Easements
Deferred credits and other liabilities
Transmission easements	$ 20,100	$ 20,500

EMPLOYEE BENEFIT PLANS - Postre

EMPLOYEE BENEFIT PLANS - Postretirement Benefits Other Than Pensions, Obligations (Details) $ in Thousands	9 Months Ended
	Sep. 30, 2020USD ($)plan
Medical Plans
Postretirement medical benefit and postemployment medical benefit obligations
End of period	$ 10,791
Postretirement Medical Benefit Plans
Postretirement medical benefit and postemployment medical benefit obligations
Beginning of period	10,195
Service cost	422
Interest cost	264
Benefit payments (net of contributions by participants)	(465)
End of period	$ 10,416
Threshold percentage, unrecognized amount of actuarial gains and losses as a percentage of projected benefit obligation	10.00%
Postemployment Medical Benefit Plans
Postretirement medical benefit and postemployment medical benefit obligations
End of period	$ 375
Non-bargaining unit employees | Medical Plans
POSTRETIREMENT BENEFITS OTHER THAN PENSIONS
Number of plans | plan	3
Non-bargaining unit employees | Medical Plans | Maximum
POSTRETIREMENT BENEFITS OTHER THAN PENSIONS
Qualifying age	65 years
Non-bargaining unit employees | Postretirement Medical Benefit Plans
POSTRETIREMENT BENEFITS OTHER THAN PENSIONS
Number of plans | plan	2
Non-bargaining unit employees | Postretirement Medical Benefit Plans | Minimum
POSTRETIREMENT BENEFITS OTHER THAN PENSIONS
Qualifying age	55 years
Non-bargaining unit employees | Postemployment Medical Benefit Plans
POSTRETIREMENT BENEFITS OTHER THAN PENSIONS
Number of plans | plan	3

EMPLOYEE BENEFIT PLANS - Post_2

EMPLOYEE BENEFIT PLANS - Postretirement Benefits Other Than Pensions, Actuarial Gains and Losses (Details) - Postretirement Medical Benefit Plans $ in Thousands	9 Months Ended
	Sep. 30, 2020USD ($)
Net unrecognized actuarial gains and losses
Accumulated other comprehensive loss at beginning of period	$ (1,387)
Amortization of actuarial (gain) loss into income	11
Amortization of prior service credit into other income	(59)
Accumulated other comprehensive loss at end of period	$ (1,435)

EMPLOYEE BENEFIT PLANS - NRECA

EMPLOYEE BENEFIT PLANS - NRECA Executive Benefit Restoration Plan, Obligations (Details) - NRECA Executive Benefit Restoration Plan $ in Thousands	9 Months Ended
	Sep. 30, 2020USD ($)
Defined Benefit Plans
Beginning of period	$ 674
Service cost	312
Interest cost	417
Plan amendments - prior service cost	5,218
Benefit payments (net of contributions by participants)	(715)
Actuarial loss	2,155
End of period	$ 8,061
Threshold percentage, unrecognized amount of actuarial gains and losses as a percentage of projected benefit obligation	10.00%

EMPLOYEE BENEFIT PLANS - NREC_2

EMPLOYEE BENEFIT PLANS - NRECA Executive Benefit Restoration Plan, Actuarial Gains and Losses (Details) - NRECA Executive Benefit Restoration Plan $ in Thousands	9 Months Ended
	Sep. 30, 2020USD ($)
Net unrecognized actuarial gains and losses
Accumulated other comprehensive loss at beginning of period	$ (130)
Plan amendments - prior service cost	(5,218)
Amortization of prior service credit into other income	1,336
Unrecognized actuarial loss	(2,155)
Accumulated other comprehensive loss at end of period	$ (6,167)

REVENUE - Member (Details)

REVENUE - Member (Details)	9 Months Ended
	Sep. 30, 2020customeritem
Member electric sales
Number of billing components of Class A rate schedule for electric power sales to Members	3
Number of demand rates	2
Member Contracts Extending Through 2050
Member electric sales
Number of contracts | customer	42

REVENUE - Non-member (Details)

REVENUE - Non-member (Details) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020USD ($)	Sep. 30, 2019USD ($)	Sep. 30, 2020USD ($)item	Sep. 30, 2019USD ($)
Disaggregation of revenue
Other	$ 16,226	$ 12,128	$ 37,150	$ 39,540
Revenues	401,601	399,053	$ 1,034,723	1,053,558
Number of non-utility members from whom other operating revenue is received | item			2
Non-member electric sales and other operating revenue
Disaggregation of revenue
Revenues	54,832	40,467	$ 108,194	111,383
Non-member electric sales
Disaggregation of revenue
Revenue from contract with customer	38,606	28,339	71,044	71,843
Non-member electric sales | Long-term contracts
Disaggregation of revenue
Revenue from contract with customer	9,423	12,647	32,817	35,241
Non-member electric sales | Short-term contracts
Disaggregation of revenue
Revenue from contract with customer	29,183	15,692	38,227	36,602
Other
Disaggregation of revenue
Other	$ 16,226	$ 12,128	$ 37,150	$ 39,540

INCOME TAXES (Details)

INCOME TAXES (Details) - USD ($) $ in Thousands	3 Months Ended			9 Months Ended
	Sep. 30, 2020	Mar. 31, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
INCOME TAXES
Income tax benefit	$ 154		$ 77	$ 484	$ 231
Decrease in deferred tax valuation allowance		$ 19,000

LEASES - Leasing Arrangements a

LEASES - Leasing Arrangements as Lessee (Details) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020USD ($)	Sep. 30, 2019USD ($)	Sep. 30, 2020USD ($)leaseMW	Sep. 30, 2019USD ($)	Dec. 31, 2019USD ($)
Lease expenses
Operating lease expense	$ 1,200	$ 1,800	$ 2,800	$ 5,400
Number of financing leases | lease			0
Lessee operating lease assets and liabilities
Operating lease right-of-use assets, gross	11,464		$ 11,464		$ 8,376
Less: Accumulated amortization	(1,378)		(1,378)		(754)
Net operating lease right-of-use assets	$ 10,086		$ 10,086		7,622
Operating lease right-of-use asset, Statement of Financial Position line item	us-gaap:DeferredCostsCurrentAndNoncurrent		us-gaap:DeferredCostsCurrentAndNoncurrent
Operating lease liabilities - current	$ (556)		$ (556)		(5,533)
Operating lease liabilities - current, Statement of Financial Position line item	us-gaap:LiabilitiesCurrent		us-gaap:LiabilitiesCurrent
Operating lease liabilities - noncurrent	$ (1,705)		$ (1,705)		(1,846)
Operating lease liabilities - noncurrent, Statement of Financial Position line item	tris:OtherDeferredCreditsAndOtherLiabilities		tris:OtherDeferredCreditsAndOtherLiabilities
Total operating lease liabilities	$ (2,261)		$ (2,261)		$ (7,379)
Weighted average remaining lease term (years)	7 years 5 months 16 days		7 years 5 months 16 days		9 years 6 months
Weighted average discount rate	3.83%		3.83%		3.80%
Brush Generating Station
Operating Lease - Lessee
Megawatt usage | MW			70

LEASES - Future Minimum Lease C

LEASES - Future Minimum Lease Commitments (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Future expected minimum lease commitments under operating leases
Year 1	$ 609
Year 2	444
Year 3	341
Year 4	315
Year 5	196
Thereafter	737
Total lease payments	2,642
Less imputed interest	(381)
Total	$ 2,261	$ 7,379

LEASES - Leasing Arrangements_2

LEASES - Leasing Arrangements as Lessor (Details) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020USD ($)	Sep. 30, 2019USD ($)	Sep. 30, 2020USD ($)MW	Sep. 30, 2019USD ($)
Lease revenue | $	$ 1.8	$ 1.6	$ 5	$ 10.5
J. M. Shafer Generating Station
Megawatt usage			272
J. M. Shafer Generating Station | Third Party
Megawatt usage			122

FAIR VALUE (Details)

FAIR VALUE (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Fair value:
Regulatory liabilities	$ 237,187	$ 122,169
Principal Amount
Fair value:
Marketable securities	477	715
Long-term debt	3,314,353	3,166,472
Estimated Fair Value
Fair value:
Cash and cash equivalents	102,200	79,000
Estimated Fair Value | Level 2
Fair value:
Long-term debt	3,926,312	3,608,341
Estimated Fair Value | Recurring | Level 1
Fair value:
Marketable securities	$ 429	$ 654

VARIABLE INTEREST ENTITIES - Co

VARIABLE INTEREST ENTITIES - Consolidated Entities (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Consolidated Variable Interest Entities
Net electric plant	$ 3,339,573		$ 3,339,573		$ 3,613,846
Noncontrolling interest	113,425		113,425		111,717
Long-term debt	3,205,904		3,205,904		3,063,351
Accrued interest	45,830		45,830		29,716
Interest	$ 36,213	$ 38,030	$ 109,511	$ 113,954
Springerville Partnership
Consolidated Variable Interest Entities
Equity interest (as a percent)			51.00%
General partner interest (as a percent)			1.00%
Springerville Partnership | Springerville Unit 3 Lease
Consolidated Variable Interest Entities
Percentage of financial and other support provided			100.00%
Springerville Partnership | Springerville Unit 3 Holding LLC
Consolidated Variable Interest Entities
Ownership interest held by parent (as a percent)	100.00%		100.00%
Springerville Partnership | Reportable Legal Entities
Consolidated Variable Interest Entities
Net electric plant	$ 762,808		$ 762,808		776,411
Noncontrolling interest	113,425		113,425		111,717
Long-term debt	342,680		342,680		380,867
Accrued interest	3,977		3,977		$ 11,050
Depreciation and amortization	4,535	4,535	13,603	13,603
Interest	$ 5,646	$ 6,281	$ 17,157	$ 19,045
Other Limited Partners | Springerville Partnership
Consolidated Variable Interest Entities
Ownership interest held by noncontrolling interest (as a percent)	49.00%		49.00%

VARIABLE INTEREST ENTITIES - Un

VARIABLE INTEREST ENTITIES - Unconsolidated Entities (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Unconsolidated Variable Interest Entity - not primary beneficiary | Western Fuels Association | Investments in other associations
Unconsolidated Variable Interest Entities
Investment in unconsolidated VIE	$ 2.3	$ 2.4
Unconsolidated Variable Interest Entity - not primary beneficiary | WFW | Investments in other associations
Unconsolidated Variable Interest Entities
Investment in unconsolidated VIE	$ 0.1	0.1
MBPP
Unconsolidated Variable Interest Entities
Tri-State share (as a percent)	27.13%
WFW | Western Fuels Association | Class AA shares
Unconsolidated Variable Interest Entities
Ownership interest held by parent (as a percent)	100.00%
WFW | Western Fuels Association | Class BB Shares
Unconsolidated Variable Interest Entities
Ownership interest held by parent (as a percent)	75.00%
WFW | MBPP | Class BB Shares
Unconsolidated Variable Interest Entities
Ownership interest held by noncontrolling interest (as a percent)	25.00%
MBPP | Unconsolidated Variable Interest Entity - not primary beneficiary
Unconsolidated Variable Interest Entities
Tri-State share (as a percent)	27.13%
Trapper Mining | Unconsolidated Variable Interest Entity - not primary beneficiary
Unconsolidated Variable Interest Entities
Tri-State share (as a percent)	26.57%
Trapper Mining | Unconsolidated Variable Interest Entity - not primary beneficiary | Investments In and Advances To Coal Mines [Member]
Unconsolidated Variable Interest Entities
Investment in coal mine	$ 16.3	$ 15.9

LEGAL - Legal (Details)

LEGAL - Legal (Details) $ in Millions	May 04, 2020item	Sep. 30, 2020USD ($)
Members | Maximum
Annual allowance for self-supply of a member's electric power requirements		5.00%
United Power Complaint | Non-Utility Members
Number of codefendants | item	3
Long-term Transmission Agreement Dispute
Damages sought | $		$ 6.9