Alliance Resource Partners (ARLP) 10-Q 4 Nov 21 2021 Q3 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	9 Months Ended
	Sep. 30, 2021	Nov. 04, 2021
Document and Entity Information
Document Type	10-Q
Document Quarterly Report	true
Document Transition Report	false
Document Period End Date	Sep. 30, 2021
Entity File Number	0-26823
Entity Registrant Name	ALLIANCE RESOURCE PARTNERS LP
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	73-1564280
Entity Address, Address Line One	1717 South Boulder Avenue, Suite 400
Entity Address, City or Town	Tulsa
Entity Address, State or Province	OK
Entity Address, Postal Zip Code	74119
City Area Code	918
Local Phone Number	295-7600
Title of 12(b) Security	Common units
Trading Symbol	ARLP
Security Exchange Name	NASDAQ
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Units Outstanding		127,195,219
Entity Central Index Key	0001086600
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	Q3
Amendment Flag	false

CONDENSED CONSOLIDATED BALANCE

CONDENSED CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
CURRENT ASSETS:
Cash and cash equivalents	$ 104,611	$ 55,574
Trade receivables	142,007	104,579
Other receivables	1,064	3,481
Inventories, net	65,484	56,407
Advance royalties	2,063	4,168
Prepaid expenses and other assets	10,931	21,565
Total current assets	326,160	245,774
PROPERTY, PLANT AND EQUIPMENT:
Property, plant and equipment, at cost	3,570,201	3,554,090
Less accumulated depreciation, depletion and amortization	(1,873,987)	(1,753,845)
Total property, plant and equipment, net	1,696,214	1,800,245
OTHER ASSETS:
Advance royalties	65,034	56,791
Equity method investments	26,180	27,268
Goodwill	4,373	4,373
Operating lease right-of-use assets	14,338	15,004
Other long-term assets	16,676	16,561
Total other assets	126,601	119,997
TOTAL ASSETS	2,148,975	2,166,016
CURRENT LIABILITIES:
Accounts payable	70,425	47,511
Accrued taxes other than income taxes	23,797	25,054
Accrued payroll and related expenses	39,949	28,524
Accrued interest	12,500	5,132
Workers' compensation and pneumoconiosis benefits	10,635	10,646
Current finance lease obligations	821	766
Current operating lease obligations	1,809	1,854
Other current liabilities	14,379	21,919
Current maturities, long-term debt, net	16,770	73,199
Total current liabilities	191,085	214,605
LONG-TERM LIABILITIES:
Long-term debt, excluding current maturities, net	425,075	519,421
Pneumoconiosis benefits	107,099	105,068
Accrued pension benefit	41,220	46,965
Workers' compensation	43,818	47,521
Asset retirement obligations	122,935	121,487
Long-term finance lease obligations	835	1,458
Long-term operating lease obligations	12,722	13,078
Other liabilities	22,348	24,146
Total long-term liabilities	776,052	879,144
Total liabilities	967,137	1,093,749
COMMITMENTS AND CONTINGENCIES - (NOTE 4)
ARLP Partners' Capital:
Limited Partners - Common Unitholders 127,195,219 units outstanding	1,251,674	1,148,565
Accumulated other comprehensive loss	(80,981)	(87,674)
Total ARLP Partners' Capital	1,170,693	1,060,891
Noncontrolling interest	11,145	11,376
Total Partners' Capital	1,181,838	1,072,267
TOTAL LIABILITIES AND PARTNERS' CAPITAL	$ 2,148,975	$ 2,166,016

CONDENSED CONSOLIDATED BALANC_2

CONDENSED CONSOLIDATED BALANCE SHEETS (Parenthetical) - shares	Sep. 30, 2021	Dec. 31, 2020
CONDENSED CONSOLIDATED BALANCE SHEETS
Common units outstanding	127,195,219	127,195,219

CONDENSED CONSOLIDATED STATEMEN

CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
SALES AND OPERATING REVENUES:
Revenues	$ 415,439	$ 355,651	$ 1,096,504	$ 961,616
EXPENSES:
Outside coal purchases	6,065		6,179
General and administrative	18,655	13,871	51,651	41,131
Depreciation, depletion and amortization	68,763	80,182	192,698	237,662
Asset impairments				24,977
Goodwill impairment				132,026
Total operating expenses	348,711	316,306	938,441	1,090,051
INCOME (LOSS) FROM OPERATIONS	66,728	39,345	158,063	(128,435)
Interest expense (net of interest capitalized for the three and nine months ended September 30, 2021 and 2020 of $123, $199, $314 and $1,265, respectively)	(9,408)	(11,186)	(29,646)	(34,911)
Interest income	19	30	51	112
Equity method investment income	703	62	1,106	650
Other expense	(84)	(723)	(2,632)	(1,456)
INCOME (LOSS) BEFORE INCOME TAXES	57,958	27,528	126,942	(164,040)
INCOME TAX EXPENSE	234	293	227	111
NET INCOME (LOSS)	57,724	27,235	126,715	(164,151)
LESS: NET INCOME ATTRIBUTABLE TO NONCONTROLLING INTEREST	(176)	(36)	(384)	(97)
NET INCOME (LOSS) ATTRIBUTABLE TO ARLP	$ 57,548	$ 27,199	$ 126,331	$ (164,248)
EARNINGS PER LIMITED PARTNER UNIT - BASIC AND DILUTED	$ 0.44	$ 0.21	$ 0.97	$ (1.29)
WEIGHTED-AVERAGE NUMBER OF UNITS OUTSTANDING - BASIC AND DILUTED	127,195,219	127,195,219	127,195,219	127,154,398
Product
EXPENSES:
Operating expenses (excluding depreciation, depletion and amortization)	$ 233,201	$ 216,027	$ 642,760	$ 637,533
Coal sales
SALES AND OPERATING REVENUES:
Revenues	362,264	335,767	975,725	886,690
Oil & gas royalties
SALES AND OPERATING REVENUES:
Revenues	20,109	9,693	51,222	31,718
Transportation
SALES AND OPERATING REVENUES:
Revenues	22,027	6,226	45,153	16,722
EXPENSES:
Operating expenses (excluding depreciation, depletion and amortization)	22,027	6,226	45,153	16,722
Other revenues
SALES AND OPERATING REVENUES:
Revenues	$ 11,039	$ 3,965	$ 24,404	$ 26,486

CONDENSED CONSOLIDATED STATEM_2

CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS (Parenthetical) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS
Interest expense, interest capitalized	$ 123	$ 199	$ 314	$ 1,265

CONDENSED CONSOLIDATED STATEM_3

CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (LOSS) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
NET INCOME (LOSS)	$ 57,724	$ 27,235	$ 126,715	$ (164,151)
OTHER COMPREHENSIVE INCOME (LOSS):
OTHER COMPREHENSIVE INCOME	2,231	844	6,693	2,721
COMPREHENSIVE INCOME (LOSS)	59,955	28,079	133,408	(161,430)
Less: Comprehensive income attributable to noncontrolling interest	(176)	(36)	(384)	(97)
COMPREHENSIVE INCOME (LOSS) ATTRIBUTABLE TO ARLP	59,779	28,043	133,024	(161,527)
Defined benefit pension plan
OTHER COMPREHENSIVE INCOME (LOSS):
Amortization of prior service cost	47	47	140	140
Amortization of net actuarial loss (gain)	1,141	969	3,424	3,096
Total adjustments	1,188	1,016	3,564	3,236
Pneumoconiosis benefits
OTHER COMPREHENSIVE INCOME (LOSS):
Amortization of net actuarial loss (gain)	1,043	(172)	3,129	(515)
Total adjustments	$ 1,043	$ (172)	$ 3,129	$ (515)

CONDENSED CONSOLIDATED STATEM_4

CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	9 Months Ended		12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS
CASH FLOWS FROM OPERATING ACTIVITIES	$ 310,977	$ 291,788
Property, plant and equipment:
Capital expenditures	(88,661)	(102,820)
Change in accounts payable and accrued liabilities	2,281	(9,698)
Proceeds from sale of property, plant and equipment	6,432	2,750
Distributions received from investments in excess of cumulative earnings	1,088	841
Escrow deposit for oil & gas reserve acquisition	(1,550)
Net cash used in investing activities	(80,410)	(108,927)
CASH FLOWS FROM FINANCING ACTIVITIES:
Borrowings under securitization facility	35,000	46,100
Payments under securitization facility	(90,900)	(47,700)
Proceeds from equipment financings		14,705
Payments on equipment financings	(12,888)	(10,622)
Borrowings under revolving credit facilities	15,000	70,000
Payments under revolving credit facilities	(102,500)	(190,000)
Borrowings from line of credit	3,230
Payments on finance lease obligations	(568)	(8,204)
Payment of debt issuance costs	(113)	(5,821)
Payments for purchase of units and tax withholdings related to settlements under deferred compensation plans	(1,090)	(1,310)
Distributions paid to Partners	(26,086)	(51,753)	$ (51,753)
Other	(615)	(603)
Net cash used in financing activities	(181,530)	(185,208)
NET CHANGE IN CASH AND CASH EQUIVALENTS	49,037	(2,347)
CASH AND CASH EQUIVALENTS AT BEGINNING OF PERIOD	55,574	36,482	36,482
CASH AND CASH EQUIVALENTS AT END OF PERIOD	104,611	34,135	$ 55,574
SUPPLEMENTAL CASH FLOW INFORMATION:
Cash paid for interest	20,045	26,686
Cash paid for income taxes	11	10
SUPPLEMENTAL NON-CASH ACTIVITY:
Accounts payable for purchase of property, plant and equipment	8,012	4,806
Right-of-use assets acquired by operating lease		278
Market value of common units issued under deferred compensation plans before tax withholding requirements	$ 1,082	$ 3,837

ORGANIZATION AND PRESENTATION

ORGANIZATION AND PRESENTATION	9 Months Ended
	Sep. 30, 2021
ORGANIZATION AND PRESENTATION
ORGANIZATION AND PRESENTATION	1. ORGANIZATION AND PRESENTATION ​ Significant Relationships Referenced in Notes to Condensed Consolidated Financial Statements ​ ● References to "we," "us," "our" or "ARLP Partnership" mean the business and operations of Alliance Resource Partners, L.P., the parent company, as well as its consolidated subsidiaries. ● References to "ARLP" mean Alliance Resource Partners, L.P., individually as the parent company, and not on a consolidated basis. ● References to "MGP" mean Alliance Resource Management GP, LLC, ARLP's general partner. ● References to "Mr. Craft" mean Joseph W. Craft III, the Chairman, President and Chief Executive Officer of MGP. ● References to "Intermediate Partnership" mean Alliance Resource Operating Partners, L.P., the intermediate partnership of Alliance Resource Partners, L.P. ● References to "Alliance Coal" mean Alliance Coal, LLC, the holding company for our coal mining operations. ● References to "Alliance Minerals" mean Alliance Minerals, LLC, the holding company for our oil and gas minerals interests. ● References to "Alliance Resource Properties" mean Alliance Resource Properties, LLC, the land holding company for certain of our coal mineral interests, including the subsidiaries of Alliance Resource Properties, LLC. ​ Organization ​ ARLP is a Delaware limited partnership listed on the NASDAQ Global Select Market under the ticker symbol "ARLP." ARLP was formed in May 1999 and completed its initial public offering on August 19, 1999 when it acquired substantially all of the coal production and marketing assets of Alliance Resource Holdings, Inc., a Delaware corporation, and its subsidiaries. We are managed by our general partner, MGP, a Delaware limited liability company which holds a non-economic general partner interest in ARLP. ​ Basis of Presentation ​ The accompanying condensed consolidated financial statements include the accounts and operations of the ARLP Partnership and present our financial position as of September 30, 2021 and December 31, 2020, the results of our operations and comprehensive income (loss) for the three and nine months ended September 30, 2021 and 2020, and cash flows for the nine months ended September 30, 2021 and 2020. All intercompany transactions and accounts have been eliminated. ​ These condensed consolidated financial statements and notes are prepared pursuant to the rules and regulations of the Securities and Exchange Commission for interim reporting and do not include all the information normally included with financial statements prepared in accordance with generally accepted accounting principles ("GAAP") of the United States. These financial statements should be read in conjunction with the audited consolidated financial statements and notes thereto included in our Annual Report on Form 10-K for the year ended December 31, 2020. ​ These condensed consolidated financial statements and notes are unaudited. However, in the opinion of management, these condensed consolidated financial statements reflect all normal recurring adjustments necessary for a fair presentation of the results for the periods presented. Results for interim periods are not necessarily indicative of results to be expected for the full year ending December 31, 2021. ​ Use of Estimates ​ The preparation of the ARLP Partnership's condensed consolidated financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts and disclosures in our condensed consolidated financial statements. Actual results could differ from those estimates.

LONG-LIVED ASSET IMPAIRMENTS

LONG-LIVED ASSET IMPAIRMENTS	9 Months Ended
	Sep. 30, 2021
LONG-LIVED ASSET IMPAIRMENTS
LONG-LIVED ASSET IMPAIRMENTS	2. LONG-LIVED ASSET IMPAIRMENTS ​ During the first quarter of 2020, we recorded $23.5 million of non-cash asset impairment charges in our Illinois Basin Coal Operations segment due to sealing our idled Gibson North mine, resulting in its permanent closure, and a decrease in the fair value of certain mining equipment at our idled operations and greenfield coal reserves as a result of weakened coal market conditions. During the same period, we also recorded an asset impairment charge of $1.5 million in our Coal Royalties segment due to a decrease in the fair value of greenfield coal reserves held by Alliance Resource Properties near our coal mining operations in the Illinois Basin. See Note 16 – Segment Information for more information about our segments. ​ The fair values of the impaired assets were determined using a market approach, which represents Level 3 fair value measurements under the fair value hierarchy. The fair value analysis used assumptions regarding the marketability of certain mining and reserve assets near our Illinois Basin coal mining operations.

GOODWILL IMPAIRMENT

GOODWILL IMPAIRMENT	9 Months Ended
	Sep. 30, 2021
GOODWILL IMPAIRMENT
GOODWILL IMPAIRMENT	3. GOODWILL IMPAIRMENT ​ During the first quarter of 2020, we considered whether an interim test of our consolidated goodwill of $136.4 million was necessary. Our consolidated goodwill included $132.0 million recorded in our Illinois Basin Coal Operations segment in conjunction with our acquisition of the Hamilton County Coal, LLC ("Hamilton") mine on July 31, 2015. We assessed certain events and changes in circumstances, including a) adverse industry and market developments, including the impact of the COVID-19 pandemic, b) our response to these developments, including temporarily ceasing production at several mines, including our Hamilton mine and c) our actual performance during the quarter. After consideration of these events and changes in circumstances, we performed an interim test of the goodwill associated with Hamilton comparing Hamilton's carrying amount to its fair value. ​ We estimated the fair value of Hamilton using an income approach utilizing a discounted cash flow model. The assumptions used in the discounted cash flow model included estimated production, forward coal prices, operating expenses, capital expenditures and a weighted average cost of capital. Our forecasts of future cash flows considered market conditions at the time of the assessment and our estimate of the mine's performance in future years based on the information available to us. Key assumptions used in our valuation were not observable in active markets; therefore, the fair value measurements represent Level 3 fair value measurements. The fair value of Hamilton was determined to be below its carrying amount (including goodwill) by more than the recorded balance of goodwill associated with the mine. Accordingly, we recognized an impairment charge of $132.0 million consisting of the total carrying amount of goodwill associated with Hamilton. This impairment charge reduced our consolidated goodwill balance to $4.4 million. During the first quarter of 2020, we also performed an interim test on ARLP's remaining goodwill balances not associated with Hamilton and concluded no impairment was necessary for our other reporting units.

CONTINGENCIES

CONTINGENCIES	9 Months Ended
	Sep. 30, 2021
CONTINGENCIES
CONTINGENCIES	4. CONTINGENCIES ​ We are party to litigation that has been initiated against certain of our subsidiaries in which the plaintiffs allege violations of the Fair Labor Standards Act and Kentucky Wage and Hour Act due to an alleged failure to compensate for time "donning" and "doffing" equipment and to account for certain bonuses in the calculation of overtime rates and pay. The plaintiffs seek class or collective action certification. Because the litigation of these matters is in the early stages, we cannot reasonably estimate a range of potential exposure at this time. We believe the plaintiffs’ claims are without merit and our ultimate exposure, if any, will not be material to our results of operations or financial position and we intend to defend the litigation vigorously. However, if our current belief that the claims are without merit is not upheld, it is reasonably possible that the ultimate resolution of these matters could result in a potential loss that may be material to our results of operations. ​ We also have various other lawsuits, claims and regulatory proceedings incidental to our business that are pending against the ARLP Partnership. We record an accrual for a potential loss related to these matters when, in management's opinion, such loss is probable and reasonably estimable. Based on known facts and circumstances, we believe the ultimate outcome of these outstanding lawsuits, claims and regulatory proceedings will not have a material adverse effect on our financial condition, results of operations or liquidity. However, if the results of these matters are different from management's current expectations and in amounts greater than our accruals, such matters could have a material adverse effect on our business and operations.

INVENTORIES

INVENTORIES	9 Months Ended
	Sep. 30, 2021
INVENTORIES
INVENTORIES	5. INVENTORIES ​ Inventories consist of the following: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ September 30, ​ December 31, ​ ​ ​ 2021 2020 ​ ​ (in thousands) ​ ​ ​ ​ ​ ​ ​ ​ ​ Coal ​ $ 31,066 ​ $ 19,756 ​ Supplies (net of reserve for obsolescence of $5,554 and $5,547, respectively) ​ 34,418 ​ 36,651 ​ Total inventories, net ​ $ 65,484 ​ $ 56,407 ​ ​

FAIR VALUE MEASUREMENTS

FAIR VALUE MEASUREMENTS	9 Months Ended
	Sep. 30, 2021
FAIR VALUE MEASUREMENTS
FAIR VALUE MEASUREMENTS	6. FAIR VALUE MEASUREMENTS ​ The following table summarizes our fair value measurements within the hierarchy not included elsewhere in these notes: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ September 30, 2021 ​ December 31, 2020 ​ ​ Level 1 Level 2 Level 3 Level 1 Level 2 Level 3 ​ ​ (in thousands) ​ Long-term debt ​ $ — ​ $ 459,650 ​ $ — ​ $ — ​ $ 518,317 ​ $ — ​ Total ​ $ — ​ $ 459,650 ​ $ — ​ $ — ​ $ 518,317 ​ $ — ​ ​ The carrying amounts for cash equivalents, accounts receivable, accounts payable, accrued and other liabilities approximate fair value due to the short maturity of those instruments. ​ The estimated fair value of our long-term debt, including current maturities, is based on interest rates that we believe are currently available to us in active markets for issuance of debt with similar terms and remaining maturities (See Note 7 – Long-Term Debt). The fair value of debt, which is based upon these interest rates, is classified as a Level 2 measurement under the fair value hierarchy.

LONG-TERM DEBT

LONG-TERM DEBT	9 Months Ended
	Sep. 30, 2021
LONG-TERM DEBT
LONG-TERM DEBT	7. LONG-TERM DEBT ​ Long-term debt consists of the following: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Unamortized Discount and ​ ​ ​ Principal ​ Debt Issuance Costs ​ ​ ​ September 30, ​ December 31, ​ September 30, ​ December 31, ​ ​ 2021 2020 2021 2020 ​ ​ (in thousands) ​ Revolving credit facility ​ $ — ​ $ 87,500 ​ $ (5,599) ​ $ (7,196) ​ Senior notes ​ 400,000 ​ 400,000 ​ (3,278) ​ (3,964) ​ Securitization facility ​ ​ — ​ ​ 55,900 ​ ​ — ​ ​ — ​ May 2019 equipment financing ​ ​ 2,387 ​ ​ 4,956 ​ ​ — ​ ​ — ​ November 2019 equipment financing ​ ​ 34,617 ​ ​ 42,367 ​ ​ — ​ ​ — ​ June 2020 equipment financing ​ ​ 10,488 ​ ​ 13,057 ​ ​ — ​ ​ — ​ Line of credit ​ ​ 3,230 ​ ​ — ​ ​ — ​ ​ — ​ ​ ​ 450,722 ​ 603,780 ​ (8,877) ​ (11,160) ​ Less current maturities ​ (16,770) ​ (73,199) ​ — ​ — ​ Total long-term debt ​ $ 433,952 ​ $ 530,581 ​ $ (8,877) ​ $ (11,160) ​ ​ Credit Facility. ​ The Credit Agreement is guaranteed by certain of our Intermediate Partnership's material direct and indirect subsidiaries (the "Restricted Subsidiaries") and is secured by substantially all the assets of the Restricted Subsidiaries. The Credit Agreement is also guaranteed by Alliance Minerals but the oil and gas minerals assets of Alliance Minerals and its direct and indirect subsidiaries (collectively with Alliance Minerals, the "Unrestricted Subsidiaries") are not collateral under the Credit Agreement. Borrowings under the Revolving Credit Facility bear interest, at our option, at either (i) the Base Rate at the greater of three benchmarks or (ii) a Eurodollar Rate, plus margins for (i) or (ii), as applicable, that fluctuate depending upon the ratio of Consolidated Debt to Consolidated Cash Flow (each as defined in the Credit Agreement). The Eurodollar Rate, with applicable margin, under the Revolving Credit Facility was 2.68% as of September 30, 2021. On September 30, 2021, we had $23.3 million of letters of credit outstanding with $436.2 million available for borrowing under the Revolving Credit Facility. We incur an annual commitment fee of 0.35% on the undrawn portion of the Revolving Credit Facility. We utilize the Revolving Credit Facility, as appropriate, for working capital requirements, capital expenditures and investments, scheduled debt payments and distribution payments. ​ The Credit Agreement contains various restrictions affecting the Intermediate Partnership and its Restricted Subsidiaries including, among other things, restrictions on incurrence of additional indebtedness and liens, sale of assets, investments, mergers and consolidations and transactions with affiliates, including transactions with Unrestricted Subsidiaries. In each case, these restrictions are subject to various exceptions. In addition, the payment of cash distributions is restricted if such payment would result in a fixed charge coverage ratio of less than 1.0 to 1.0 (as defined in the Credit Agreement) for the four most recently ended fiscal quarters. The Credit Agreement requires the Intermediate Partnership to maintain (a) a debt to cash flow ratio of not more than 2.5 to 1.0, (b) a cash flow to interest expense ratio of not less than 3.0 to 1.0 and (c) a first lien debt to cash flow ratio of not more than 1.5 to 1.0, in each case, during the four most recently ended fiscal quarters. The debt to cash flow ratio, cash flow to interest expense ratio and first lien debt to cash flow ratio were 0.95 to 1.0, 11.60 to 1.0 and 0.10 to 1.0, respectively, for the trailing twelve months ended September 30, 2021. We remained in compliance with the covenants of the Credit Agreement as of September 30, 2021 and anticipate remaining in compliance with the covenants. ​ Senior Notes. On April 24, 2017, the Intermediate Partnership and Alliance Resource Finance Corporation (as co-issuer), a wholly owned subsidiary of the Intermediate Partnership ("Alliance Finance"), issued an aggregate principal amount of $400.0 million of senior unsecured notes due 2025 ("Senior Notes") in a private placement to qualified institutional buyers. The Senior Notes have a term of eight years , maturing on May 1, 2025 (the "Term") and accrue interest at an annual rate of 7.5% . Interest is payable semi-annually in arrears on each May 1 and November 1. The indenture governing the Senior Notes contains customary terms, events of default and covenants relating to, among other things, the incurrence of debt, the payment of distributions or similar restricted payments, undertaking transactions with affiliates and limitations on asset sales. The issuers of the Senior Notes may redeem all or a part of the notes at any time at redemption prices set forth in the indenture governing the Senior Notes. ​ Accounts Receivable Securitization. ​ May 2019 Equipment Financing . On May 17, 2019, the Intermediate Partnership entered into an equipment financing arrangement accounted for as debt, wherein the Intermediate Partnership received $10.0 million in exchange for conveying its interest in certain equipment owned indirectly by the Intermediate Partnership and entering into a master lease agreement for that equipment (the "May 2019 Equipment Financing"). The May 2019 Equipment Financing contains customary terms and events of default and provides for thirty-six monthly payments with an implicit interest rate of 6.25% , maturing on May 1, 2022. Upon maturity, the equipment will revert to the Intermediate Partnership. ​ November 2019 Equipment Financing. On November 6, 2019, the Intermediate Partnership entered into an equipment financing arrangement accounted for as debt, wherein the Intermediate Partnership received $53.1 million in exchange for conveying its interest in certain equipment owned indirectly by the Intermediate Partnership and entering into a master lease agreement for that equipment (the "November 2019 Equipment Financing"). The November 2019 Equipment Financing contains customary terms and events of default and an implicit interest rate of 4.75% , providing for a four-year term with forty-seven monthly payments of $1.0 million and a balloon payment of $11.6 million upon maturity on November 6, 2023. Upon maturity, the equipment will revert to the Intermediate Partnership. ​ June 2020 Equipment Financing. On June 5, 2020, the Intermediate Partnership entered into an equipment financing arrangement accounted for as debt, wherein the Intermediate Partnership received $14.7 million in exchange for conveying its interest in certain equipment owned indirectly by the Intermediate Partnership and entering into a master lease agreement for that equipment (the "June 2020 Equipment Financing"). The June 2020 Equipment Financing contains customary terms and events of default and provides for forty-eight monthly payments with an implicit interest rate of 6.1% , maturing on June 5, 2024. Upon maturity, the equipment will revert to the Intermediate Partnership. ​ Line of Credit. On February 19, 2021, we entered into a line of credit arrangement with a related party for $5.0 million. The line of credit has a maturity date of February 28, 2023, with an option to extend it for an additional six months and accrue interest at an annual rate of 3.50% . Interest is payable quarterly commencing March 31, 2021, and continuing each March 31, June 30, September 30 and December 31 thereafter through and including February 28, 2023. The agreement contains customary terms and events of default and is guaranteed by ARLP. We utilize the line of credit, as appropriate, for capital expenditures and investments. As of September 30, 2021, we had drawn $3.2 million under this agreement.

VARIABLE INTEREST ENTITIES

VARIABLE INTEREST ENTITIES	9 Months Ended
	Sep. 30, 2021
VARIABLE INTEREST ENTITIES
VARIABLE INTEREST ENTITIES	8. VARIABLE INTEREST ENTITIES ​ Cavalier Minerals ​ On November 10, 2014, our subsidiary, Alliance Minerals, and Bluegrass Minerals Management, LLC ("Bluegrass Minerals") entered into a limited liability company agreement (the "Cavalier Agreement") to create Cavalier Minerals JV, LLC ("Cavalier Minerals"), which was formed to indirectly acquire oil & gas mineral interests through its ownership in AllDale Minerals LP ("AllDale I") and AllDale Minerals II, LP ("AllDale II", and collectively with AllDale I, "AllDale I & II"). Alliance Minerals owns a 96% member interest in Cavalier Minerals, and Bluegrass Minerals owns a 4% member interest in Cavalier Minerals and a profits interest which entitles it to receive distributions equal to 25% of all distributions (including in liquidation) after all members have recovered their investment. Distributions with respect to Bluegrass Minerals' profits interest will be offset by all distributions received by Bluegrass Minerals from the former general partners of AllDale I & II. To date, there has been no profits interest distribution. We hold the managing member interest in Cavalier Minerals. Total contributions to and cumulative distributions from Cavalier Minerals are as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Alliance ​ Bluegrass ​ ​ ​ Minerals ​ Minerals ​ ​ ​ (in thousands) ​ Contributions ​ $ 143,112 ​ $ 5,963 ​ Distributions ​ ​ 104,149 ​ ​ 4,339 ​ ​ We have concluded that Cavalier Minerals is a variable interest entity ("VIE") which we consolidate as the primary beneficiary because we are the managing member and a substantial equity owner in Cavalier Minerals. Bluegrass Minerals' equity ownership of Cavalier Minerals is accounted for as noncontrolling ownership interest in our condensed consolidated balance sheets. In addition, earnings attributable to Bluegrass Minerals are recognized as noncontrolling interest in our condensed consolidated statements of operations. ​ AllDale III ​ In February 2017, Alliance Minerals committed to directly invest $30.0 million in AllDale Minerals III, LP ("AllDale III") which was created for similar investment purposes as AllDale I & II. Alliance Minerals completed funding of this commitment in 2018. ​ The AllDale III Partnership Agreement includes a 25% profits interest for the general partner, subject to a return hurdle equal to the greater of 125% of cumulative capital contributions and a 10% internal rate of return, and following an 80/20 "catch-up" provision for the general partner. ​ Since AllDale III is structured as a limited partnership with the limited partners 1) not having the ability to remove the general partner and 2) not participating significantly in the operational decisions, we concluded that AllDale III is a VIE.

INVESTMENT

INVESTMENT	9 Months Ended
	Sep. 30, 2021
INVESTMENT
INVESTMENT	9. INVESTMENT ​ AllDale III ​ As discussed in Note 8 – Variable Interest Entities, we account for our ownership interest in the income or loss of AllDale III as an equity method investment. We record equity income or loss based on AllDale III's distribution structure. The changes in our equity method investment in AllDale III for each of the periods presented were as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Three Months Ended ​ Nine Months Ended ​ ​ ​ September 30, ​ September 30, ​ ​ 2021 2020 2021 2020 ​ ​ ​ (in thousands) ​ Beginning balance ​ $ 26,274 ​ $ 27,705 ​ $ 27,268 ​ $ 28,529 ​ Equity method investment income ​ ​ 703 ​ ​ 62 ​ ​ 1,106 ​ ​ 650 ​ Distributions received ​ ​ (797) ​ ​ (352) ​ ​ (2,194) ​ ​ (1,491) ​ Other ​ ​ — ​ ​ — ​ ​ — ​ ​ (273) ​ Ending balance ​ $ 26,180 ​ $ 27,415 ​ $ 26,180 ​ $ 27,415 ​ ​

PARTNERS' CAPITAL

PARTNERS' CAPITAL	9 Months Ended
	Sep. 30, 2021
PARTNERS' CAPITAL
PARTNERS' CAPITAL	10. PARTNERS' CAPITAL ​ Distributions ​ Distributions paid or declared during 2020 and 2021 were as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ Payment Date Per Unit Cash Distribution Total Cash Distribution ​ ​ ​ ​ ​ (in thousands) ​ ​ ​ ​ ​ ​ ​ ​ ​ February 14, 2020 ​ $ 0.4000 ​ $ 51,753 ​ Total ​ $ 0.4000 ​ $ 51,753 ​ ​ ​ ​ ​ ​ ​ ​ ​ May 14, 2021 ​ $ 0.1000 ​ $ 13,045 ​ August 13, 2021 ​ ​ 0.1000 ​ ​ 13,041 ​ November 12, 2021 (1) ​ ​ 0.2000 ​ ​ — ​ Total ​ $ 0.4000 ​ $ 26,086 ​ (1) On October 25, 2021, we declared this quarterly distribution payable on November 12, 2021 to all unitholders of record as of November 5, 2021 . ​ Unit Repurchase Program ​ In May 2018, the MGP board of directors approved the establishment of a unit repurchase program authorizing us to repurchase and retire up to $100 million of ARLP common units. The program has no time limit and we may repurchase units from time to time in the open market or in other privately negotiated transactions. The unit repurchase program authorization does not obligate us to repurchase any dollar amount or number of units. No unit repurchases were made during the nine months ended September 30, 2021. Since inception of the unit repurchase program, we have repurchased and retired 5,460,639 units at an average unit price of $17.12 for an aggregate purchase price of $93.5 million. ​ Change in Partners' Capital ​ The following tables present the quarterly change in Partners' Capital for the nine months ended September 30, 2021 and 2020: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Accumulated ​ ​ ​ ​ ​ ​ ​ ​ ​ Number of ​ Limited ​ Other ​ ​ ​ ​ ​ ​ ​ ​ ​ Limited Partner ​ Partners' ​ Comprehensive ​ Noncontrolling ​ Total Partners' ​ ​ Units Capital Income (Loss) Interest Capital ​ ​ (in thousands, except unit data) ​ Balance at January 1, 2021 127,195,219 ​ $ 1,148,565 ​ $ (87,674) ​ $ 11,376 ​ $ 1,072,267 ​ Comprehensive income: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Net income — ​ 24,748 ​ — ​ ​ 78 24,826 ​ Actuarially determined long-term liability adjustments — ​ — ​ 2,231 ​ — 2,231 ​ Total comprehensive income ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 27,057 ​ Common unit-based compensation — ​ 723 ​ ​ — ​ ​ — ​ ​ 723 ​ Distributions from consolidated company to noncontrolling interest ​ — ​ ​ — ​ ​ — ​ ​ (141) ​ ​ (141) ​ Balance at March 31, 2021 ​ 127,195,219 ​ ​ 1,174,036 ​ ​ (85,443) ​ ​ 11,313 ​ ​ 1,099,906 ​ Comprehensive income: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Net income — ​ 44,035 ​ — ​ ​ 130 44,165 ​ Actuarially determined long-term liability adjustments — ​ — ​ 2,231 ​ — 2,231 ​ Total comprehensive income ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 46,396 ​ Common unit-based compensation — ​ 1,485 ​ ​ — ​ ​ — ​ ​ 1,485 ​ Distributions on deferred common unit-based compensation — ​ (324) ​ ​ — ​ ​ — ​ ​ (324) ​ Distributions from consolidated company to noncontrolling interest ​ — ​ ​ — ​ ​ — ​ ​ (222) ​ ​ (222) ​ Distributions to Partners — ​ ​ (12,721) ​ ​ — ​ ​ — ​ ​ (12,721) ​ Balance at June 30, 2021 ​ 127,195,219 ​ ​ 1,206,511 ​ ​ (83,212) ​ ​ 11,221 ​ ​ 1,134,520 ​ Comprehensive income: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Net income — ​ 57,548 ​ — ​ ​ 176 57,724 ​ Actuarially determined long-term liability adjustments — ​ — ​ 2,231 ​ — 2,231 ​ Total comprehensive income ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 59,955 ​ Settlement of deferred compensation plans ​ ​ ​ ​ (1,090) ​ ​ — ​ ​ — ​ ​ (1,090) ​ Common unit-based compensation — ​ 1,746 ​ ​ — ​ ​ — ​ ​ 1,746 ​ Distributions on deferred common unit-based compensation — ​ (323) ​ ​ — ​ ​ — ​ ​ (323) ​ Distributions from consolidated company to noncontrolling interest ​ — ​ ​ — ​ ​ — ​ ​ (252) ​ ​ (252) ​ Distributions to Partners — ​ ​ (12,718) ​ ​ — ​ ​ — ​ ​ (12,718) ​ Balance at September 30, 2021 127,195,219 ​ $ 1,251,674 ​ $ (80,981) ​ $ 11,145 ​ $ 1,181,838 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Accumulated ​ ​ ​ ​ ​ ​ ​ ​ ​ Number of ​ Limited ​ Other ​ ​ ​ ​ ​ ​ ​ ​ ​ Limited Partner ​ Partners' ​ Comprehensive ​ Noncontrolling ​ Total Partners' ​ ​ Units Capital Income (Loss) Interest Capital ​ ​ (in thousands, except unit data) ​ Balance at January 1, 2020 126,915,597 ​ $ 1,331,482 ​ $ (77,993) ​ $ 11,935 ​ $ 1,265,424 ​ Comprehensive income (loss): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Net income (loss) — ​ (144,783) ​ — ​ ​ 76 (144,707) ​ Actuarially determined long-term liability adjustments — ​ — ​ 938 ​ — 938 ​ Total comprehensive loss ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ (143,769) ​ Settlement of deferred compensation plans ​ 279,622 ​ ​ (1,310) ​ ​ — ​ ​ — ​ ​ (1,310) ​ Common unit-based compensation — ​ (527) ​ ​ — ​ ​ — ​ ​ (527) ​ Distributions on deferred common unit-based compensation — ​ (986) ​ ​ — ​ ​ — ​ ​ (986) ​ Distributions from consolidated company to noncontrolling interest ​ — ​ ​ — ​ ​ — ​ ​ (288) ​ ​ (288) ​ Distributions to Partners — ​ ​ (50,767) ​ ​ — ​ ​ — ​ ​ (50,767) ​ Other ​ — ​ ​ (273) ​ ​ — ​ ​ — ​ ​ (273) ​ Balance at March 31, 2020 127,195,219 ​ ​ 1,132,836 ​ ​ (77,055) ​ ​ 11,723 ​ ​ 1,067,504 ​ Comprehensive income (loss): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Net loss — ​ (46,664) ​ — ​ ​ (15) (46,679) ​ Actuarially determined long-term liability adjustments — ​ — ​ 939 ​ — 939 ​ Total comprehensive loss ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ (45,740) ​ Common unit-based compensation — ​ 1,610 ​ ​ — ​ ​ — ​ ​ 1,610 ​ Distributions from consolidated company to noncontrolling interest ​ — ​ ​ — ​ ​ — ​ ​ (222) ​ ​ (222) ​ Balance at June 30, 2020 127,195,219 ​ ​ 1,087,782 ​ ​ (76,116) ​ ​ 11,486 ​ ​ 1,023,152 ​ Comprehensive income: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Net income — ​ 27,199 ​ — ​ ​ 36 27,235 ​ Actuarially determined long-term liability adjustments — ​ — ​ 844 ​ — 844 ​ Total comprehensive income ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 28,079 ​ Common unit-based compensation — ​ 1,645 ​ ​ — ​ ​ — ​ ​ 1,645 ​ Distributions from consolidated company to noncontrolling interest ​ — ​ ​ — ​ ​ — ​ ​ (93) ​ ​ (93) ​ Balance at September 30, 2020 127,195,219 ​ $ 1,116,626 ​ $ (75,272) ​ $ 11,429 ​ $ 1,052,783 ​ ​

REVENUE FROM CONTRACTS WITH CUS

REVENUE FROM CONTRACTS WITH CUSTOMERS	9 Months Ended
	Sep. 30, 2021
REVENUE FROM CONTRACTS WITH CUSTOMERS
REVENUE FROM CONTRACTS WITH CUSTOMERS	11. REVENUE FROM CONTRACTS WITH CUSTOMERS ​ The following table illustrates the disaggregation of our revenues by type, including a reconciliation to our segment presentation as presented in Note 16 – Segment Information. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Coal Operations ​ Royalties ​ Other, ​ ​ ​ ​ ​ ​ Illinois ​ ​ ​ ​ Corporate and ​ ​ ​ ​ Basin Appalachia Oil & Gas Coal Elimination Consolidated ​ ​ ​ (in thousands) ​ Three Months Ended September 30, 2021 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Coal sales ​ $ 217,637 ​ $ 144,627 ​ $ — ​ $ — ​ $ — ​ $ 362,264 ​ Oil & gas royalties ​ ​ — ​ ​ — ​ ​ 20,109 ​ ​ — ​ ​ — ​ ​ 20,109 ​ Coal royalties ​ ​ — ​ ​ — ​ ​ — ​ ​ 13,456 ​ ​ (13,456) ​ ​ — ​ Transportation revenues ​ ​ 12,121 ​ ​ 9,906 ​ ​ — ​ ​ — ​ ​ — ​ ​ 22,027 ​ Other revenues ​ ​ 1,335 ​ ​ 411 ​ ​ 1,082 ​ ​ — ​ ​ 8,211 ​ ​ 11,039 ​ Total revenues ​ $ 231,093 ​ $ 154,944 ​ $ 21,191 ​ $ 13,456 ​ $ (5,245) ​ $ 415,439 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Three Months Ended September 30, 2020 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Coal sales ​ $ 206,356 ​ $ 129,411 ​ $ — ​ $ — ​ $ — ​ $ 335,767 ​ Oil & gas royalties ​ ​ — ​ ​ — ​ ​ 9,693 ​ ​ — ​ ​ — ​ ​ 9,693 ​ Coal royalties ​ ​ — ​ ​ — ​ ​ — ​ ​ 11,406 ​ ​ (11,406) ​ ​ — ​ Transportation revenues ​ ​ 3,722 ​ ​ 2,504 ​ ​ — ​ ​ — ​ ​ — ​ ​ 6,226 ​ Other revenues ​ ​ 241 ​ ​ 395 ​ ​ 28 ​ ​ 42 ​ ​ 3,259 ​ ​ 3,965 ​ Total revenues ​ $ 210,319 ​ $ 132,310 ​ $ 9,721 ​ $ 11,448 ​ $ (8,147) ​ $ 355,651 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Nine Months Ended September 30, 2021 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Coal sales ​ $ 610,435 ​ $ 365,290 ​ $ — ​ $ — ​ $ — ​ $ 975,725 ​ Oil & gas royalties ​ ​ — ​ ​ — ​ ​ 51,222 ​ ​ — ​ ​ — ​ ​ 51,222 ​ Coal royalties ​ ​ — ​ ​ — ​ ​ — ​ ​ 36,410 ​ ​ (36,410) ​ ​ — ​ Transportation revenues ​ ​ 27,235 ​ ​ 17,918 ​ ​ — ​ ​ — ​ ​ — ​ ​ 45,153 ​ Other revenues ​ ​ 2,590 ​ ​ 1,078 ​ ​ 1,576 ​ ​ — ​ ​ 19,160 ​ ​ 24,404 ​ Total revenues ​ $ 640,260 ​ $ 384,286 ​ $ 52,798 ​ $ 36,410 ​ $ (17,250) ​ $ 1,096,504 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Nine Months Ended September 30, 2020 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Coal sales ​ $ 539,614 ​ $ 347,076 ​ $ — ​ $ — ​ $ — ​ $ 886,690 ​ Oil & gas royalties ​ ​ — ​ ​ — ​ ​ 31,718 ​ ​ — ​ ​ — ​ ​ 31,718 ​ Coal royalties ​ ​ — ​ ​ — ​ ​ — ​ ​ 29,555 ​ ​ (29,555) ​ ​ — ​ Transportation revenues ​ ​ 10,731 ​ ​ 5,991 ​ ​ — ​ ​ — ​ ​ — ​ ​ 16,722 ​ Other revenues ​ ​ 1,633 ​ ​ 14,456 ​ ​ 113 ​ ​ 47 ​ ​ 10,237 ​ ​ 26,486 ​ Total revenues ​ $ 551,978 ​ $ 367,523 ​ $ 31,831 ​ $ 29,602 ​ $ (19,318) ​ $ 961,616 ​ ​ The following table illustrates the amount of our transaction price for all current coal supply contracts allocated to performance obligations that are unsatisfied or partially unsatisfied as of September 30, 2021 and disaggregated by segment and contract duration. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 2024 and ​ ​ ​ 2021 2022 2023 Thereafter Total ​ ​ (in thousands) ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Illinois Basin Coal Operations coal revenues ​ $ 293,651 ​ $ 567,699 ​ $ 255,470 ​ $ 196,683 ​ $ 1,313,503 Appalachia Coal Operations coal revenues ​ ​ 183,060 ​ ​ 325,846 ​ ​ 17,880 ​ ​ 10,080 ​ ​ 536,866 Total coal revenues (1) ​ $ 476,711 ​ $ 893,545 ​ $ 273,350 ​ $ 206,763 ​ $ 1,850,369 (1) Coal revenues generally consists of consolidated revenues excluding our Oil & Gas Royalties segment as well as intercompany revenues from our Coal Royalties segment .

EARNINGS PER LIMITED PARTNER UN

EARNINGS PER LIMITED PARTNER UNIT	9 Months Ended
	Sep. 30, 2021
EARNINGS PER LIMITED PARTNER UNIT
EARNINGS PER LIMITED PARTNER UNIT	12. EARNINGS PER LIMITED PARTNER UNIT ​ We utilize the two-class method in calculating basic and diluted earnings per limited partner unit ("EPU"). Net income attributable to ARLP is allocated to limited partners and participating securities under deferred compensation plans, which include rights to nonforfeitable distributions or distribution equivalents. Net losses attributable to ARLP are allocated to limited partners but not to participating securities. Our participating securities are outstanding restricted unit awards under our Long-Term Incentive Plan ("LTIP") and phantom units in notional accounts under our Supplemental Executive Retirement Plan ("SERP") and the MGP Amended and Restated Deferred Compensation Plan for Directors ("Directors' Deferred Compensation Plan"). ​ The following is a reconciliation of net income (loss) attributable to ARLP used for calculating basic and diluted earnings per unit and the weighted-average units used in computing EPU for the three and nine months ended September 30, 2021 and 2020: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Three Months Ended ​ Nine Months Ended ​ ​ ​ September 30, ​ September 30, ​ ​ 2021 2020 2021 2020 ​ ​ (in thousands, except per unit data) ​ Net income (loss) attributable to ARLP ​ $ 57,548 ​ $ 27,199 ​ $ 126,331 ​ $ (164,248) ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Less: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Distributions to participating securities ​ (765) ​ — ​ (1,384) ​ — ​ Undistributed earnings attributable to participating securities ​ (951) ​ (581) ​ (1,832) ​ — ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Net income (loss) attributable to ARLP available to limited partners ​ $ 55,832 ​ $ 26,618 ​ $ 123,115 ​ $ (164,248) ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted-average limited partner units outstanding – basic and diluted ​ 127,195 ​ 127,195 ​ 127,195 ​ 127,154 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Earnings per limited partner unit - basic and diluted (1) ​ $ 0.44 ​ $ 0.21 ​ $ 0.97 ​ $ (1.29) ​ (1) Diluted EPU gives effect to all potentially dilutive common units outstanding during the period using the treasury stock method. Diluted EPU excludes all potentially dilutive units calculated under the treasury stock method if their effect is anti-dilutive. The combined total of LTIP, SERP and Directors' Deferred Compensation Plan units of 2,328 and 1,706 for the three and nine months ended September 30, 2021 , respectively, and 661 and 656 for the three and nine months ended September 30, 2020, respectively, were considered anti-dilutive under the treasury stock method .

WORKERS' COMPENSATION AND PNEUM

WORKERS' COMPENSATION AND PNEUMOCONIOSIS	9 Months Ended
	Sep. 30, 2021
WORKERS' COMPENSATION AND PNEUMOCONIOSIS BENEFITS
WORKERS' COMPENSATION AND PNEUMOCONIOSIS	13. WORKERS' COMPENSATION AND PNEUMOCONIOSIS ​ The changes in the workers' compensation liability, including current and long-term liability balances, for each of the periods presented were as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Three Months Ended ​ Nine Months Ended ​ ​ September 30, ​ September 30, ​ ​ ​ 2021 2020 2021 2020 ​ ​ ​ (in thousands) ​ Beginning balance ​ $ 52,059 ​ $ 54,478 ​ $ 54,739 ​ $ 53,384 ​ Accruals increase ​ 1,674 ​ 1,599 ​ 4,911 ​ 3,539 ​ Payments ​ (2,939) ​ (2,123) ​ (7,914) ​ (6,686) ​ Interest accretion ​ 232 ​ 319 ​ 695 ​ 958 ​ Valuation loss (gain) (1) ​ — ​ — ​ (1,405) ​ 3,078 ​ Ending balance ​ $ 51,026 ​ $ 54,273 ​ $ 51,026 ​ $ 54,273 ​ (1) Our estimate of the liability for the present value of current workers′ compensation benefits is based on our actuarial calculations. Our actuarial calculations are based on a blend of actuarial projection methods and numerous assumptions including claims development patterns, mortality, medical costs and interest rates. The valuation gain in 2021 is due to an increase in the discount rate from 1.95% on December 31, 2020 to 2.34% on June 30, 202 1 . We conducted a mid-year 2020 review of our actuarial assumptions, which resulted in a valuation loss in 2020 due to unfavorable changes in claims development and a decrease in the discount rate from 2.81% on December 31, 2019 to 2.05% on June 30, 2020. ​ We limit our exposure to traumatic injury claims by purchasing a high deductible insurance policy that starts paying benefits after deductibles for a claim have been met. The deductible level may vary by claim year. Our workers' compensation liability above is presented on a gross basis and does not include our expected receivables on our insurance policy. Our receivables for traumatic injury claims under this policy as of September 30, 2021 are $7.1 million and are included in Other long-term assets ​ Certain of our mine operating entities are liable under state statutes and the Federal Coal Mine Health and Safety Act of 1969, as amended, to pay pneumoconiosis, or black lung, benefits to eligible employees and former employees and their dependents. Components of the net periodic benefit cost for each of the periods presented are as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Three Months Ended ​ Nine Months Ended ​ ​ ​ September 30, ​ September 30, ​ ​ ​ 2021 2020 2021 2020 ​ ​ (in thousands) ​ Service cost ​ $ 1,007 ​ $ 882 ​ $ 3,027 ​ $ 2,643 Interest cost (1) ​ 636 ​ 750 ​ 1,909 ​ 2,249 ​ Net amortization (1) ​ 1,043 ​ (172) ​ 3,129 ​ (515) ​ Net periodic benefit cost ​ $ 2,686 ​ $ 1,460 ​ $ 8,065 ​ $ 4,377 ​ (1) Interest cost and net amortization are included in the Other expense line item within our condensed consolidated statements of operations.

COMMON UNIT-BASED COMPENSATION

COMMON UNIT-BASED COMPENSATION PLANS	9 Months Ended
	Sep. 30, 2021
COMMON UNIT-BASED COMPENSATION PLANS
COMMON UNIT-BASED COMPENSATION PLANS	14. COMMON UNIT-BASED COMPENSATION PLANS ​ Long-Term Incentive Plan ​ We maintain the LTIP for certain employees and officers of MGP and its affiliates who perform services for us. As part of our LTIP, unit awards of non-vested "phantom" or notional units, also referred to as "restricted units", may be granted which upon satisfaction of time and performance-based vesting requirements, entitle the LTIP participant to receive ARLP common units. Certain awards may also contain a minimum-value guarantee payable in ARLP common units or cash that would be paid regardless of whether or not the awards vest, as long as service requirements are met. Annual grant levels, vesting provisions and minimum-value guarantees of restricted units for designated participants are recommended by Mr. Craft, subject to review and approval of the compensation committee of the MGP board of directors (the "Compensation Committee"). Vesting of all restricted units outstanding is subject to the satisfaction of certain financial tests. If it is not probable the financial tests for a particular grant of restricted units will be met, any previously expensed amounts for that grant are reversed and no future expense will be recognized for that grant. Assuming the financial tests are met, grants of restricted units issued to LTIP participants are generally expected to cliff vest on January 1st of the third year following issuance of the grants. We expect to settle restricted unit grants by delivery of newly-issued ARLP common units, except for the portion of the grants that will satisfy employee tax withholding obligations of LTIP participants. We account for forfeitures of non-vested LTIP restricted unit grants as they occur. As provided under the distribution equivalent rights ("DERs") provisions of the LTIP and the terms of the LTIP restricted unit awards, all non-vested restricted units include contingent rights to receive quarterly distributions in cash or, at the discretion of the Compensation Committee, phantom units in lieu of cash credited to a bookkeeping account with value equal to the cash distributions we make to unitholders during the vesting period. If it is not probable the financial tests for a particular grant of restricted units will be met, any previously paid DER amounts for that grant are reversed from Partners’ Capital and recorded as compensation expense and any future DERs, for that grant, if any, will be recognized as compensation expense when paid. ​ A summary of non-vested LTIP grants as of and for the nine months ended September 30, 2021 is as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Number of units Weighted average grant date fair value per unit Intrinsic value ​ ​ ​ ​ ​ ​ ​ (in thousands) ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Non-vested grants at January 1, 2021 ​ 1,430,489 ​ $ 5.02 ​ $ 6,409 ​ Granted (1) 1,818,190 ​ ​ 6.03 ​ ​ ​ ​ Forfeited (69,933) ​ 5.46 ​ ​ ​ ​ Non-vested grants at September 30, 2021 3,178,746 ​ 5.59 ​ ​ 34,553 ​ (1) 921,430 units and 896,760 units have a minimum-value guarantee of $2.53 and $3.79 per unit, respectively, regardless of whether or not the awards vest. ​ LTIP expense for grants of restricted units was $1.7 million and $1.6 million for the three months ended September 30, 2021 and 2020, respectively, and $3.8 million and $2.5 million for the nine months ended September 30, 2021 and 2020, respectively. LTIP expense for grants of restricted units for the nine months ended September 30, 2020 includes the reversal of $4.8 million of cumulative previously recognized expense for the 2019 Grants, which were determined to be not probable of vesting, offset in part by related DERs for the 2019 Grants previously recorded to equity and then expensed. ​ The total obligation associated with LTIP grants of restricted units as of September 30, 2021 was $ 5.1 million and is included in the partners' capital Limited partners-common unitholders line item in our condensed consolidated balance sheets. As of September 30, 2021, there was $12.6 million in total unrecognized compensation expense related to the non-vested LTIP restricted unit grants that are expected to vest. That expense is expected to be recognized over a weighted-average period of 1.8 years. ​ Supplemental Executive Retirement Plan and Directors' Deferred Compensation Plan ​ We utilize the SERP to provide deferred compensation benefits for certain officers and key employees. All allocations made to participants under the SERP are made in the form of "phantom" ARLP units and SERP distributions will be settled in the form of ARLP common units. The SERP is administered by the Compensation Committee. ​ Our directors participate in the Directors' Deferred Compensation Plan. Pursuant to the Directors' Deferred Compensation Plan, for amounts deferred either automatically or at the election of the director, a notional account is established and credited with notional common units of ARLP, described in the Directors' Deferred Compensation Plan as "phantom" units. Distributions from the Directors' Deferred Compensation Plan will be settled in the form of ARLP common units. ​ For both the SERP and Directors' Deferred Compensation Plan, when quarterly cash distributions are made with respect to ARLP common units, an amount equal to such quarterly distribution is credited to each participant's notional account as additional phantom units. All grants of phantom units under the SERP and Directors' Deferred Compensation Plan vest immediately. ​ A summary of SERP and Directors' Deferred Compensation Plan activity as of and for the nine months ended September 30, 2021 is as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Number of units Weighted average grant date fair value per unit Intrinsic value ​ ​ ​ ​ ​ ​ ​ (in thousands) ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Phantom units outstanding as of January 1, 2021 ​ 760,630 ​ $ 22.04 ​ $ 3,408 ​ Granted ​ 22,777 ​ ​ 6.97 ​ ​ ​ ​ Issued (1) (138,570) ​ ​ 25.86 ​ ​ ​ ​ Phantom units outstanding as of September 30, 2021 644,837 ​ 20.69 ​ ​ 7,009 ​ (1) During the nine months ended September 30, 2021, we issued 102,962 ARLP common units purchased on the open market to a participant under the SERP. Units issued were net of units settled in cash to satisfy tax withholding obligations. ​ Total SERP and Directors' Deferred Compensation Plan expense was $0.1 million for the three months ended September 30, 2021 and 2020, and $0.3 million and $0.4 million for the nine months ended September 30, 2021, and 2020, respectively. As of September 30, 2021, the total obligation associated with the SERP and Directors' Deferred Compensation Plan was $13.3 million and is included in the partners' capital Limited partners-common unitholders

COMPONENTS OF PENSION PLAN NET

COMPONENTS OF PENSION PLAN NET PERIODIC BENEFIT COSTS	9 Months Ended
	Sep. 30, 2021
COMPONENTS OF PENSION PLAN NET PERIODIC BENEFIT COSTS
COMPONENTS OF PENSION PLAN NET PERIODIC BENEFIT COSTS	15. COMPONENTS OF PENSION PLAN NET PERIODIC BENEFIT COSTS ​ Eligible employees at certain of our mining operations participate in a defined benefit plan (the "Pension Plan") that we sponsor. The Pension Plan is currently closed to new applicants and participants in the Pension Plan are no longer receiving benefit accruals for service. The benefit formula for the Pension Plan is a fixed dollar unit based on years of service. Components of the net periodic benefit cost for each of the periods presented are as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Three Months Ended ​ Nine Months Ended ​ ​ ​ September 30, ​ September 30, ​ ​ ​ 2021 2020 2021 2020 ​ ​ (in thousands) ​ Interest cost ​ $ 860 ​ $ 1,030 ​ $ 2,580 ​ $ 3,138 ​ Expected return on plan assets ​ (1,671) ​ (1,413) ​ (5,013) ​ (4,396) ​ Amortization of prior service cost ​ ​ 47 ​ ​ 47 ​ ​ 140 ​ ​ 140 ​ Amortization of net loss ​ 1,141 ​ 969 ​ 3,424 ​ 3,096 ​ Net periodic benefit cost (1) ​ $ 377 ​ $ 633 ​ $ 1,131 ​ $ 1,978 ​ (1) Net periodic benefit cost for the Pension Plan is included in the Other expense line item within our condensed consolidated statements of operations. ​ During the nine months ended September 30, 2021, we made contribution payments totaling $3.3 million to the Pension Plan for the 2020 plan year. As a result of certain pension plan contribution relief provided by the American Rescue Plan Act enacted in March 2021, we do not expect to make additional contributions to the Pension Plan during 2021 or 2022.

SEGMENT INFORMATION

SEGMENT INFORMATION	9 Months Ended
	Sep. 30, 2021
SEGMENT INFORMATION
SEGMENT INFORMATION	16. SEGMENT INFORMATION ​ We operate in the United States as a diversified natural resource company that generates operating and royalty income from the production and marketing of coal to major domestic and international utilities and industrial users as well as royalty income from oil & gas mineral interests. We aggregate multiple operating segments into four reportable segments, Illinois Basin Coal Operations, Appalachia Coal Operations, Oil & Gas Royalties and Coal Royalties. We also have an "all other" category referred to as Other, Corporate and Elimination. ​ Our two coal operations reportable segments correspond to major coal producing regions in the eastern United States with similar economic characteristics including coal quality, geology, coal marketing opportunities, mining and transportation methods and regulatory issues. The two coal operations reportable segments include seven mining complexes operating in Illinois, Indiana, Kentucky, Maryland, ​ Beginning in the first quarter of 2021, we began to strategically view and manage our coal royalty activities separately from our coal mining operations since acquiring and managing a variety of royalty producing assets have similar management attributes. As a result, we restructured our reportable segments to better reflect this strategic view in how we manage our business and allocate resources. Prior periods have been recast to include Alliance Resource Properties within our new Coal Royalties reportable segment with offsetting recast adjustments primarily to our coal operations reportable segments and to a lesser extent, our Other, Corporate and Elimination category. Eliminations reported in Other, Corporate and Elimination were also recast to reflect intercompany royalty revenues and offsetting intercompany royalty expense resulting from our new Coal Royalties reportable segment. ​ The Illinois Basin Coal Operations reportable segment includes currently operating mining complexes (a) the Gibson County Coal, LLC ("Gibson") mining complex, which includes the Gibson South mine, (b) the Warrior Coal, LLC ("Warrior") mining complex, (c) the River View Coal, LLC ("River View") mining complex and (d) the Hamilton mining complex. The Illinois Basin Coal Operations reportable segment also includes our currently operating Mt. Vernon Transfer Terminal, LLC ("Mt. Vernon") coal loading terminal in Indiana on the Ohio River. Our Coal Royalties reportable segment discussed below, controls other coal reserves near our Illinois Basin operations which have not yet been leased to our Illinois Basin mining entities. ​ The Illinois Basin Coal Operations reportable segment also includes Mid-America Carbonates, LLC ("MAC") and other support services as well as non-operating mining complexes including (a) the Gibson North mine, which ceased production in the fourth quarter of 2019, (b) Webster County Coal, LLC's Dotiki mining complex, (c) White County Coal, LLC's Pattiki mining complex, (d) Hopkins County Coal, LLC's mining complex, and (e) Sebree Mining, LLC's mining complex. ​ The Appalachia Coal Operations reportable segment includes currently operating mining complexes (a) the Mettiki mining complex, (b) the Tunnel Ridge, LLC mining complex ("Tunnel Ridge") and (c) the MC Mining, LLC mining complex. The Mettiki mining complex includes Mettiki Coal (WV), LLC's Mountain View mine and Mettiki Coal, LLC's preparation plant. ​ The Oil & Gas Royalties reportable segment includes oil & gas mineral interests held by AR Midland, LP and AllDale I & II and includes Alliance Minerals' equity interests in both AllDale III (Note 9 – Investment) and Cavalier Minerals. ​ The Coal Royalties reportable segment includes coal reserves controlled by Alliance Resource Properties, that are either (a) leased to certain of our mining complexes in both the Illinois Basin Coal Operations and Appalachia Coal Operations reportable segments or (b) near our coal mining operations but not yet leased to our coal mining entities. About two thirds of the coal sold by our Coal Operations' mines is leased from our Coal Royalties entities. ​ Other, Corporate and Elimination includes marketing and administrative activities, Matrix Design Group, LLC and its subsidiaries ("Matrix Design"), Alliance Design Group, LLC ("Alliance Design") (collectively, Matrix Design and Alliance Design referred to as the "Matrix Group"), Pontiki Coal, LLC's workers' compensation and pneumoconiosis liabilities, Wildcat Insurance, LLC ("Wildcat Insurance"), which assists the ARLP Partnership with its insurance requirements, AROP Funding and Alliance Finance (both discussed in Note 7 – Long-Term Debt) and other miscellaneous activities. The eliminations included in Other, Corporate and Elimination primarily represent the intercompany coal royalty transactions described above between our Coal Royalties reportable segment and our coal operations' mines. ​ Reportable segment results are presented below. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Coal Operations ​ Royalties ​ Other, ​ ​ ​ ​ ​ Illinois ​ ​ ​ ​ ​ Corporate and ​ ​ ​ ​ Basin Appalachia Oil & Gas Coal ​ Elimination Consolidated ​ ​ (in thousands) Three Months Ended September 30, 2021 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Revenues - Outside ​ $ 231,093 ​ $ 154,944 ​ $ 21,191 ​ $ — ​ $ 8,211 ​ $ 415,439 ​ Revenues - Intercompany ​ ​ — ​ ​ — ​ ​ — ​ ​ 13,456 ​ ​ (13,456) ​ ​ — ​ Total revenues (1) ​ ​ 231,093 ​ ​ 154,944 ​ ​ 21,191 ​ ​ 13,456 ​ ​ (5,245) ​ ​ 415,439 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Segment Adjusted EBITDA Expense (2) ​ 149,666 ​ 92,312 ​ 2,639 ​ 4,258 ​ (9,525) ​ 239,350 ​ Segment Adjusted EBITDA (3) ​ 69,305 ​ 52,726 ​ 19,080 ​ 9,198 ​ 4,280 ​ 154,589 ​ Capital expenditures ​ 19,081 ​ 12,531 ​ — ​ 30 ​ 1,393 ​ 33,035 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Three Months Ended September 30, 2020 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Revenues - Outside ​ $ 210,319 ​ $ 132,310 ​ $ 9,721 ​ $ 42 ​ $ 3,259 ​ $ 355,651 ​ Revenues - Intercompany ​ ​ — ​ ​ — ​ ​ — ​ ​ 11,406 ​ ​ (11,406) ​ ​ — ​ Total revenues (1) ​ ​ 210,319 ​ ​ 132,310 ​ ​ 9,721 ​ ​ 11,448 ​ ​ (8,147) ​ ​ 355,651 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Segment Adjusted EBITDA Expense (2) ​ 131,014 ​ 86,701 ​ 849 ​ 5,161 ​ (6,975) ​ 216,750 ​ Segment Adjusted EBITDA (3) ​ 75,583 ​ 43,105 ​ 8,898 ​ 6,287 ​ (1,172) ​ 132,701 ​ Capital expenditures ​ 3,815 ​ 14,541 ​ — ​ — ​ 219 ​ 18,575 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Nine Months Ended September 30, 2021 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Revenues - Outside ​ $ 640,260 ​ $ 384,286 ​ $ 52,798 ​ $ — ​ $ 19,160 ​ $ 1,096,504 ​ Revenues - Intercompany ​ ​ — ​ ​ — ​ ​ — ​ ​ 36,410 ​ ​ (36,410) ​ ​ — ​ Total revenues (1) ​ ​ 640,260 ​ ​ 384,286 ​ ​ 52,798 ​ ​ 36,410 ​ ​ (17,250) ​ ​ 1,096,504 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Segment Adjusted EBITDA Expense (2) ​ 415,423 ​ ​ 240,494 ​ ​ 7,116 ​ ​ 13,157 ​ ​ (24,619) ​ 651,571 ​ Segment Adjusted EBITDA (3) ​ 197,601 ​ ​ 125,873 ​ ​ 46,405 ​ ​ 23,253 ​ ​ 7,370 ​ 400,502 ​ Total assets ​ 703,060 ​ ​ 422,504 ​ ​ 601,695 ​ ​ 289,100 ​ ​ 132,616 ​ 2,148,975 ​ Capital expenditures ​ 47,997 ​ ​ 34,579 ​ ​ — ​ ​ 30 ​ ​ 6,055 ​ 88,661 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Nine Months Ended September 30, 2020 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Revenues - Outside ​ $ 551,978 ​ $ 367,523 ​ $ 31,831 ​ $ 47 ​ $ 10,237 ​ $ 961,616 ​ Revenues - Intercompany ​ ​ — ​ ​ — ​ ​ — ​ ​ 29,555 ​ ​ (29,555) ​ ​ — ​ Total revenues (1) ​ ​ 551,978 ​ ​ 367,523 ​ ​ 31,831 ​ ​ 29,602 ​ ​ (19,318) ​ ​ 961,616 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Segment Adjusted EBITDA Expense (2) ​ 399,664 ​ ​ 240,846 ​ ​ 2,851 ​ ​ 12,649 ​ ​ (17,021) ​ 638,989 ​ Segment Adjusted EBITDA (3) ​ 141,583 ​ ​ 120,686 ​ ​ 29,534 ​ ​ 16,953 ​ ​ (2,298) ​ 306,458 ​ Total assets ​ 799,936 ​ ​ 461,751 ​ ​ 616,491 ​ ​ 291,854 ​ ​ 61,308 ​ 2,231,340 ​ Capital expenditures ​ 44,073 ​ ​ 57,798 ​ ​ — ​ ​ — ​ ​ 949 ​ 102,820 ​ (1) Revenues included in the Other, Corporate and Elimination column are attributable to intercompany eliminations, which are primarily the coal royalties intercompany eliminations, outside revenues at the Matrix Group and other outside miscellaneous sales and revenue activities. ​ (2) Segment Adjusted EBITDA Expense includes operating expenses, coal purchases and other income. Transportation expenses are excluded as transportation revenues are recognized in an amount equal to transportation expenses when title passes to the customer. ​ ​ The following is a reconciliation of consolidated Segment Adjusted EBITDA Expense to Operating expenses (excluding depreciation, depletion and amortization) ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Three Months Ended ​ Nine Months Ended ​ ​ ​ September 30, ​ September 30, ​ ​ ​ 2021 2020 2021 2020 ​ ​ (in thousands) ​ Segment Adjusted EBITDA Expense ​ $ 239,350 ​ $ 216,750 ​ $ 651,571 ​ $ 638,989 ​ Outside coal purchases ​ (6,065) ​ — ​ (6,179) ​ — ​ Other expense ​ (84) ​ (723) ​ (2,632) ​ (1,456) ​ Operating expenses (excluding depreciation, depletion and amortization) ​ $ 233,201 ​ $ 216,027 ​ $ 642,760 ​ $ 637,533 ​ ​ (3) Segment Adjusted EBITDA is defined as net income (loss) attributable to ARLP before net interest expense, income taxes, depreciation, depletion and amortization, general and administrative expenses and asset and goodwill impairments. Management therefore is able to focus solely on the evaluation of segment operating profitability as it relates to our revenues and operating expenses, which are primarily controlled by our segments. Consolidated Segment Adjusted EBITDA is reconciled to net income as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Three Months Ended ​ Nine Months Ended ​ ​ ​ September 30, ​ September 30, ​ ​ ​ 2021 2020 2021 2020 ​ ​ (in thousands) ​ Consolidated Segment Adjusted EBITDA ​ $ 154,589 ​ $ 132,701 ​ $ 400,502 ​ $ 306,458 ​ General and administrative ​ (18,655) ​ (13,871) ​ (51,651) ​ (41,131) ​ Depreciation, depletion and amortization ​ (68,763) ​ (80,182) ​ (192,698) ​ (237,662) ​ Asset impairments ​ — ​ — ​ — ​ (24,977) ​ Goodwill impairment ​ ​ — ​ ​ — ​ ​ — ​ ​ (132,026) ​ Interest expense, net ​ (9,389) ​ (11,156) ​ (29,595) ​ (34,799) ​ Income tax expense ​ (234) ​ (293) ​ (227) ​ (111) ​ Net income (loss) attributable to ARLP ​ $ 57,548 ​ $ 27,199 ​ $ 126,331 ​ $ (164,248) ​ Noncontrolling interest ​ ​ 176 ​ ​ 36 ​ ​ 384 ​ ​ 97 ​ Net income (loss) ​ $ 57,724 ​ $ 27,235 ​ $ 126,715 ​ $ (164,151) ​ ​

SUBSEQUENT EVENTS

SUBSEQUENT EVENTS	9 Months Ended
	Sep. 30, 2021
SUBSEQUENT EVENTS
SUBSEQUENT EVENTS	17. SUBSEQUENT EVENTS ​ Other than the events described below and in Note 10, there were no subsequent events. ​ On October 13, 2021, ARLP acquired approximately 1,480 oil & gas net royalty acres in the Delaware Basin from Boulders Royalty Corp. for a purchase price of $31.0 million, which was funded with cash on hand. ​

ORGANIZATION AND PRESENTATION (

ORGANIZATION AND PRESENTATION (Policies)	9 Months Ended
	Sep. 30, 2021
ORGANIZATION AND PRESENTATION
Basis of Presentation	Basis of Presentation ​ The accompanying condensed consolidated financial statements include the accounts and operations of the ARLP Partnership and present our financial position as of September 30, 2021 and December 31, 2020, the results of our operations and comprehensive income (loss) for the three and nine months ended September 30, 2021 and 2020, and cash flows for the nine months ended September 30, 2021 and 2020. All intercompany transactions and accounts have been eliminated. ​ These condensed consolidated financial statements and notes are prepared pursuant to the rules and regulations of the Securities and Exchange Commission for interim reporting and do not include all the information normally included with financial statements prepared in accordance with generally accepted accounting principles ("GAAP") of the United States. These financial statements should be read in conjunction with the audited consolidated financial statements and notes thereto included in our Annual Report on Form 10-K for the year ended December 31, 2020. ​ These condensed consolidated financial statements and notes are unaudited. However, in the opinion of management, these condensed consolidated financial statements reflect all normal recurring adjustments necessary for a fair presentation of the results for the periods presented. Results for interim periods are not necessarily indicative of results to be expected for the full year ending December 31, 2021. ​
Use of Estimates	Use of Estimates ​ The preparation of the ARLP Partnership's condensed consolidated financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts and disclosures in our condensed consolidated financial statements. Actual results could differ from those estimates.

INVENTORIES (Tables)

INVENTORIES (Tables)	9 Months Ended
	Sep. 30, 2021
INVENTORIES
Schedule of inventories	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ September 30, ​ December 31, ​ ​ ​ 2021 2020 ​ ​ (in thousands) ​ ​ ​ ​ ​ ​ ​ ​ ​ Coal ​ $ 31,066 ​ $ 19,756 ​ Supplies (net of reserve for obsolescence of $5,554 and $5,547, respectively) ​ 34,418 ​ 36,651 ​ Total inventories, net ​ $ 65,484 ​ $ 56,407 ​

FAIR VALUE MEASUREMENTS (Tables

FAIR VALUE MEASUREMENTS (Tables)	9 Months Ended
	Sep. 30, 2021
FAIR VALUE MEASUREMENTS
Summary of fair value measurements within the hierarchy	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ September 30, 2021 ​ December 31, 2020 ​ ​ Level 1 Level 2 Level 3 Level 1 Level 2 Level 3 ​ ​ (in thousands) ​ Long-term debt ​ $ — ​ $ 459,650 ​ $ — ​ $ — ​ $ 518,317 ​ $ — ​ Total ​ $ — ​ $ 459,650 ​ $ — ​ $ — ​ $ 518,317 ​ $ — ​

LONG-TERM DEBT (Tables)

LONG-TERM DEBT (Tables)	9 Months Ended
	Sep. 30, 2021
LONG-TERM DEBT
Schedule of long-term debt	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Unamortized Discount and ​ ​ ​ Principal ​ Debt Issuance Costs ​ ​ ​ September 30, ​ December 31, ​ September 30, ​ December 31, ​ ​ 2021 2020 2021 2020 ​ ​ (in thousands) ​ Revolving credit facility ​ $ — ​ $ 87,500 ​ $ (5,599) ​ $ (7,196) ​ Senior notes ​ 400,000 ​ 400,000 ​ (3,278) ​ (3,964) ​ Securitization facility ​ ​ — ​ ​ 55,900 ​ ​ — ​ ​ — ​ May 2019 equipment financing ​ ​ 2,387 ​ ​ 4,956 ​ ​ — ​ ​ — ​ November 2019 equipment financing ​ ​ 34,617 ​ ​ 42,367 ​ ​ — ​ ​ — ​ June 2020 equipment financing ​ ​ 10,488 ​ ​ 13,057 ​ ​ — ​ ​ — ​ Line of credit ​ ​ 3,230 ​ ​ — ​ ​ — ​ ​ — ​ ​ ​ 450,722 ​ 603,780 ​ (8,877) ​ (11,160) ​ Less current maturities ​ (16,770) ​ (73,199) ​ — ​ — ​ Total long-term debt ​ $ 433,952 ​ $ 530,581 ​ $ (8,877) ​ $ (11,160) ​

VARIABLE INTEREST ENTITIES (Tab

VARIABLE INTEREST ENTITIES (Tables)	9 Months Ended
	Sep. 30, 2021
VARIABLE INTEREST ENTITIES
Schedule of distributions	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Alliance ​ Bluegrass ​ ​ ​ Minerals ​ Minerals ​ ​ ​ (in thousands) ​ Contributions ​ $ 143,112 ​ $ 5,963 ​ Distributions ​ ​ 104,149 ​ ​ 4,339 ​

INVESTMENT (Tables)

INVESTMENT (Tables)	9 Months Ended
	Sep. 30, 2021
INVESTMENT
Schedule of changes in equity method investment	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Three Months Ended ​ Nine Months Ended ​ ​ ​ September 30, ​ September 30, ​ ​ 2021 2020 2021 2020 ​ ​ ​ (in thousands) ​ Beginning balance ​ $ 26,274 ​ $ 27,705 ​ $ 27,268 ​ $ 28,529 ​ Equity method investment income ​ ​ 703 ​ ​ 62 ​ ​ 1,106 ​ ​ 650 ​ Distributions received ​ ​ (797) ​ ​ (352) ​ ​ (2,194) ​ ​ (1,491) ​ Other ​ ​ — ​ ​ — ​ ​ — ​ ​ (273) ​ Ending balance ​ $ 26,180 ​ $ 27,415 ​ $ 26,180 ​ $ 27,415 ​

PARTNERS' CAPITAL (Tables)

PARTNERS' CAPITAL (Tables)	9 Months Ended
	Sep. 30, 2021
PARTNERS' CAPITAL
Summary of quarterly per unit distribution paid	​ ​ ​ ​ ​ ​ ​ ​ Payment Date Per Unit Cash Distribution Total Cash Distribution ​ ​ ​ ​ ​ (in thousands) ​ ​ ​ ​ ​ ​ ​ ​ ​ February 14, 2020 ​ $ 0.4000 ​ $ 51,753 ​ Total ​ $ 0.4000 ​ $ 51,753 ​ ​ ​ ​ ​ ​ ​ ​ ​ May 14, 2021 ​ $ 0.1000 ​ $ 13,045 ​ August 13, 2021 ​ ​ 0.1000 ​ ​ 13,041 ​ November 12, 2021 (1) ​ ​ 0.2000 ​ ​ — ​ Total ​ $ 0.4000 ​ $ 26,086 ​ (1) On October 25, 2021, we declared this quarterly distribution payable on November 12, 2021 to all unitholders of record as of November 5, 2021 .
Summary of changes to Partners' Capital	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Accumulated ​ ​ ​ ​ ​ ​ ​ ​ ​ Number of ​ Limited ​ Other ​ ​ ​ ​ ​ ​ ​ ​ ​ Limited Partner ​ Partners' ​ Comprehensive ​ Noncontrolling ​ Total Partners' ​ ​ Units Capital Income (Loss) Interest Capital ​ ​ (in thousands, except unit data) ​ Balance at January 1, 2021 127,195,219 ​ $ 1,148,565 ​ $ (87,674) ​ $ 11,376 ​ $ 1,072,267 ​ Comprehensive income: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Net income — ​ 24,748 ​ — ​ ​ 78 24,826 ​ Actuarially determined long-term liability adjustments — ​ — ​ 2,231 ​ — 2,231 ​ Total comprehensive income ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 27,057 ​ Common unit-based compensation — ​ 723 ​ ​ — ​ ​ — ​ ​ 723 ​ Distributions from consolidated company to noncontrolling interest ​ — ​ ​ — ​ ​ — ​ ​ (141) ​ ​ (141) ​ Balance at March 31, 2021 ​ 127,195,219 ​ ​ 1,174,036 ​ ​ (85,443) ​ ​ 11,313 ​ ​ 1,099,906 ​ Comprehensive income: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Net income — ​ 44,035 ​ — ​ ​ 130 44,165 ​ Actuarially determined long-term liability adjustments — ​ — ​ 2,231 ​ — 2,231 ​ Total comprehensive income ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 46,396 ​ Common unit-based compensation — ​ 1,485 ​ ​ — ​ ​ — ​ ​ 1,485 ​ Distributions on deferred common unit-based compensation — ​ (324) ​ ​ — ​ ​ — ​ ​ (324) ​ Distributions from consolidated company to noncontrolling interest ​ — ​ ​ — ​ ​ — ​ ​ (222) ​ ​ (222) ​ Distributions to Partners — ​ ​ (12,721) ​ ​ — ​ ​ — ​ ​ (12,721) ​ Balance at June 30, 2021 ​ 127,195,219 ​ ​ 1,206,511 ​ ​ (83,212) ​ ​ 11,221 ​ ​ 1,134,520 ​ Comprehensive income: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Net income — ​ 57,548 ​ — ​ ​ 176 57,724 ​ Actuarially determined long-term liability adjustments — ​ — ​ 2,231 ​ — 2,231 ​ Total comprehensive income ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 59,955 ​ Settlement of deferred compensation plans ​ ​ ​ ​ (1,090) ​ ​ — ​ ​ — ​ ​ (1,090) ​ Common unit-based compensation — ​ 1,746 ​ ​ — ​ ​ — ​ ​ 1,746 ​ Distributions on deferred common unit-based compensation — ​ (323) ​ ​ — ​ ​ — ​ ​ (323) ​ Distributions from consolidated company to noncontrolling interest ​ — ​ ​ — ​ ​ — ​ ​ (252) ​ ​ (252) ​ Distributions to Partners — ​ ​ (12,718) ​ ​ — ​ ​ — ​ ​ (12,718) ​ Balance at September 30, 2021 127,195,219 ​ $ 1,251,674 ​ $ (80,981) ​ $ 11,145 ​ $ 1,181,838 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Accumulated ​ ​ ​ ​ ​ ​ ​ ​ ​ Number of ​ Limited ​ Other ​ ​ ​ ​ ​ ​ ​ ​ ​ Limited Partner ​ Partners' ​ Comprehensive ​ Noncontrolling ​ Total Partners' ​ ​ Units Capital Income (Loss) Interest Capital ​ ​ (in thousands, except unit data) ​ Balance at January 1, 2020 126,915,597 ​ $ 1,331,482 ​ $ (77,993) ​ $ 11,935 ​ $ 1,265,424 ​ Comprehensive income (loss): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Net income (loss) — ​ (144,783) ​ — ​ ​ 76 (144,707) ​ Actuarially determined long-term liability adjustments — ​ — ​ 938 ​ — 938 ​ Total comprehensive loss ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ (143,769) ​ Settlement of deferred compensation plans ​ 279,622 ​ ​ (1,310) ​ ​ — ​ ​ — ​ ​ (1,310) ​ Common unit-based compensation — ​ (527) ​ ​ — ​ ​ — ​ ​ (527) ​ Distributions on deferred common unit-based compensation — ​ (986) ​ ​ — ​ ​ — ​ ​ (986) ​ Distributions from consolidated company to noncontrolling interest ​ — ​ ​ — ​ ​ — ​ ​ (288) ​ ​ (288) ​ Distributions to Partners — ​ ​ (50,767) ​ ​ — ​ ​ — ​ ​ (50,767) ​ Other ​ — ​ ​ (273) ​ ​ — ​ ​ — ​ ​ (273) ​ Balance at March 31, 2020 127,195,219 ​ ​ 1,132,836 ​ ​ (77,055) ​ ​ 11,723 ​ ​ 1,067,504 ​ Comprehensive income (loss): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Net loss — ​ (46,664) ​ — ​ ​ (15) (46,679) ​ Actuarially determined long-term liability adjustments — ​ — ​ 939 ​ — 939 ​ Total comprehensive loss ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ (45,740) ​ Common unit-based compensation — ​ 1,610 ​ ​ — ​ ​ — ​ ​ 1,610 ​ Distributions from consolidated company to noncontrolling interest ​ — ​ ​ — ​ ​ — ​ ​ (222) ​ ​ (222) ​ Balance at June 30, 2020 127,195,219 ​ ​ 1,087,782 ​ ​ (76,116) ​ ​ 11,486 ​ ​ 1,023,152 ​ Comprehensive income: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Net income — ​ 27,199 ​ — ​ ​ 36 27,235 ​ Actuarially determined long-term liability adjustments — ​ — ​ 844 ​ — 844 ​ Total comprehensive income ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 28,079 ​ Common unit-based compensation — ​ 1,645 ​ ​ — ​ ​ — ​ ​ 1,645 ​ Distributions from consolidated company to noncontrolling interest ​ — ​ ​ — ​ ​ — ​ ​ (93) ​ ​ (93) ​ Balance at September 30, 2020 127,195,219 ​ $ 1,116,626 ​ $ (75,272) ​ $ 11,429 ​ $ 1,052,783 ​

REVENUE FROM CONTRACTS WITH C_2

REVENUE FROM CONTRACTS WITH CUSTOMERS (Tables)	9 Months Ended
	Sep. 30, 2021
REVENUE FROM CONTRACTS WITH CUSTOMERS
Schedule of disaggregation of revenues by type	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Coal Operations ​ Royalties ​ Other, ​ ​ ​ ​ ​ ​ Illinois ​ ​ ​ ​ Corporate and ​ ​ ​ ​ Basin Appalachia Oil & Gas Coal Elimination Consolidated ​ ​ ​ (in thousands) ​ Three Months Ended September 30, 2021 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Coal sales ​ $ 217,637 ​ $ 144,627 ​ $ — ​ $ — ​ $ — ​ $ 362,264 ​ Oil & gas royalties ​ ​ — ​ ​ — ​ ​ 20,109 ​ ​ — ​ ​ — ​ ​ 20,109 ​ Coal royalties ​ ​ — ​ ​ — ​ ​ — ​ ​ 13,456 ​ ​ (13,456) ​ ​ — ​ Transportation revenues ​ ​ 12,121 ​ ​ 9,906 ​ ​ — ​ ​ — ​ ​ — ​ ​ 22,027 ​ Other revenues ​ ​ 1,335 ​ ​ 411 ​ ​ 1,082 ​ ​ — ​ ​ 8,211 ​ ​ 11,039 ​ Total revenues ​ $ 231,093 ​ $ 154,944 ​ $ 21,191 ​ $ 13,456 ​ $ (5,245) ​ $ 415,439 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Three Months Ended September 30, 2020 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Coal sales ​ $ 206,356 ​ $ 129,411 ​ $ — ​ $ — ​ $ — ​ $ 335,767 ​ Oil & gas royalties ​ ​ — ​ ​ — ​ ​ 9,693 ​ ​ — ​ ​ — ​ ​ 9,693 ​ Coal royalties ​ ​ — ​ ​ — ​ ​ — ​ ​ 11,406 ​ ​ (11,406) ​ ​ — ​ Transportation revenues ​ ​ 3,722 ​ ​ 2,504 ​ ​ — ​ ​ — ​ ​ — ​ ​ 6,226 ​ Other revenues ​ ​ 241 ​ ​ 395 ​ ​ 28 ​ ​ 42 ​ ​ 3,259 ​ ​ 3,965 ​ Total revenues ​ $ 210,319 ​ $ 132,310 ​ $ 9,721 ​ $ 11,448 ​ $ (8,147) ​ $ 355,651 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Nine Months Ended September 30, 2021 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Coal sales ​ $ 610,435 ​ $ 365,290 ​ $ — ​ $ — ​ $ — ​ $ 975,725 ​ Oil & gas royalties ​ ​ — ​ ​ — ​ ​ 51,222 ​ ​ — ​ ​ — ​ ​ 51,222 ​ Coal royalties ​ ​ — ​ ​ — ​ ​ — ​ ​ 36,410 ​ ​ (36,410) ​ ​ — ​ Transportation revenues ​ ​ 27,235 ​ ​ 17,918 ​ ​ — ​ ​ — ​ ​ — ​ ​ 45,153 ​ Other revenues ​ ​ 2,590 ​ ​ 1,078 ​ ​ 1,576 ​ ​ — ​ ​ 19,160 ​ ​ 24,404 ​ Total revenues ​ $ 640,260 ​ $ 384,286 ​ $ 52,798 ​ $ 36,410 ​ $ (17,250) ​ $ 1,096,504 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Nine Months Ended September 30, 2020 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Coal sales ​ $ 539,614 ​ $ 347,076 ​ $ — ​ $ — ​ $ — ​ $ 886,690 ​ Oil & gas royalties ​ ​ — ​ ​ — ​ ​ 31,718 ​ ​ — ​ ​ — ​ ​ 31,718 ​ Coal royalties ​ ​ — ​ ​ — ​ ​ — ​ ​ 29,555 ​ ​ (29,555) ​ ​ — ​ Transportation revenues ​ ​ 10,731 ​ ​ 5,991 ​ ​ — ​ ​ — ​ ​ — ​ ​ 16,722 ​ Other revenues ​ ​ 1,633 ​ ​ 14,456 ​ ​ 113 ​ ​ 47 ​ ​ 10,237 ​ ​ 26,486 ​ Total revenues ​ $ 551,978 ​ $ 367,523 ​ $ 31,831 ​ $ 29,602 ​ $ (19,318) ​ $ 961,616 ​
Schedule of current coal supply contracts allocated to performance obligations that are unsatisfied or partially unsatisfied	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 2024 and ​ ​ ​ 2021 2022 2023 Thereafter Total ​ ​ (in thousands) ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Illinois Basin Coal Operations coal revenues ​ $ 293,651 ​ $ 567,699 ​ $ 255,470 ​ $ 196,683 ​ $ 1,313,503 Appalachia Coal Operations coal revenues ​ ​ 183,060 ​ ​ 325,846 ​ ​ 17,880 ​ ​ 10,080 ​ ​ 536,866 Total coal revenues (1) ​ $ 476,711 ​ $ 893,545 ​ $ 273,350 ​ $ 206,763 ​ $ 1,850,369 (1) Coal revenues generally consists of consolidated revenues excluding our Oil & Gas Royalties segment as well as intercompany revenues from our Coal Royalties segment .

EARNINGS PER LIMITED PARTNER _2

EARNINGS PER LIMITED PARTNER UNIT (Tables)	9 Months Ended
	Sep. 30, 2021
EARNINGS PER LIMITED PARTNER UNIT
Reconciliation of net income and EPU calculations	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Three Months Ended ​ Nine Months Ended ​ ​ ​ September 30, ​ September 30, ​ ​ 2021 2020 2021 2020 ​ ​ (in thousands, except per unit data) ​ Net income (loss) attributable to ARLP ​ $ 57,548 ​ $ 27,199 ​ $ 126,331 ​ $ (164,248) ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Less: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Distributions to participating securities ​ (765) ​ — ​ (1,384) ​ — ​ Undistributed earnings attributable to participating securities ​ (951) ​ (581) ​ (1,832) ​ — ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Net income (loss) attributable to ARLP available to limited partners ​ $ 55,832 ​ $ 26,618 ​ $ 123,115 ​ $ (164,248) ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted-average limited partner units outstanding – basic and diluted ​ 127,195 ​ 127,195 ​ 127,195 ​ 127,154 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Earnings per limited partner unit - basic and diluted (1) ​ $ 0.44 ​ $ 0.21 ​ $ 0.97 ​ $ (1.29) ​ (1) Diluted EPU gives effect to all potentially dilutive common units outstanding during the period using the treasury stock method. Diluted EPU excludes all potentially dilutive units calculated under the treasury stock method if their effect is anti-dilutive. The combined total of LTIP, SERP and Directors' Deferred Compensation Plan units of 2,328 and 1,706 for the three and nine months ended September 30, 2021 , respectively, and 661 and 656 for the three and nine months ended September 30, 2020, respectively, were considered anti-dilutive under the treasury stock method .

WORKERS' COMPENSATION AND PNE_2

WORKERS' COMPENSATION AND PNEUMOCONIOSIS (Tables)	9 Months Ended
	Sep. 30, 2021
Accrued Workers Compensation And Pneumoconiosis Benefits
Reconciliation of changes in workers' compensation liability	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Three Months Ended ​ Nine Months Ended ​ ​ September 30, ​ September 30, ​ ​ ​ 2021 2020 2021 2020 ​ ​ ​ (in thousands) ​ Beginning balance ​ $ 52,059 ​ $ 54,478 ​ $ 54,739 ​ $ 53,384 ​ Accruals increase ​ 1,674 ​ 1,599 ​ 4,911 ​ 3,539 ​ Payments ​ (2,939) ​ (2,123) ​ (7,914) ​ (6,686) ​ Interest accretion ​ 232 ​ 319 ​ 695 ​ 958 ​ Valuation loss (gain) (1) ​ — ​ — ​ (1,405) ​ 3,078 ​ Ending balance ​ $ 51,026 ​ $ 54,273 ​ $ 51,026 ​ $ 54,273 ​ (1) Our estimate of the liability for the present value of current workers′ compensation benefits is based on our actuarial calculations. Our actuarial calculations are based on a blend of actuarial projection methods and numerous assumptions including claims development patterns, mortality, medical costs and interest rates. The valuation gain in 2021 is due to an increase in the discount rate from 1.95% on December 31, 2020 to 2.34% on June 30, 202 1 . We conducted a mid-year 2020 review of our actuarial assumptions, which resulted in a valuation loss in 2020 due to unfavorable changes in claims development and a decrease in the discount rate from 2.81% on December 31, 2019 to 2.05% on June 30, 2020.
Pneumoconiosis benefits
Accrued Workers Compensation And Pneumoconiosis Benefits
Components of net periodic benefit cost	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Three Months Ended ​ Nine Months Ended ​ ​ ​ September 30, ​ September 30, ​ ​ ​ 2021 2020 2021 2020 ​ ​ (in thousands) ​ Service cost ​ $ 1,007 ​ $ 882 ​ $ 3,027 ​ $ 2,643 Interest cost (1) ​ 636 ​ 750 ​ 1,909 ​ 2,249 ​ Net amortization (1) ​ 1,043 ​ (172) ​ 3,129 ​ (515) ​ Net periodic benefit cost ​ $ 2,686 ​ $ 1,460 ​ $ 8,065 ​ $ 4,377 ​ (1) Interest cost and net amortization are included in the Other expense line item within our condensed consolidated statements of operations.

COMMON UNIT-BASED COMPENSATIO_2

COMMON UNIT-BASED COMPENSATION PLANS (Tables)	9 Months Ended
	Sep. 30, 2021
COMMON UNIT-BASED COMPENSATION PLANS
Summary of non-vested share activity	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Number of units Weighted average grant date fair value per unit Intrinsic value ​ ​ ​ ​ ​ ​ ​ (in thousands) ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Non-vested grants at January 1, 2021 ​ 1,430,489 ​ $ 5.02 ​ $ 6,409 ​ Granted (1) 1,818,190 ​ ​ 6.03 ​ ​ ​ ​ Forfeited (69,933) ​ 5.46 ​ ​ ​ ​ Non-vested grants at September 30, 2021 3,178,746 ​ 5.59 ​ ​ 34,553 ​ (1) 921,430 units and 896,760 units have a minimum-value guarantee of $2.53 and $3.79 per unit, respectively, regardless of whether or not the awards vest.
Summary of activity in share-based plans	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Number of units Weighted average grant date fair value per unit Intrinsic value ​ ​ ​ ​ ​ ​ ​ (in thousands) ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Phantom units outstanding as of January 1, 2021 ​ 760,630 ​ $ 22.04 ​ $ 3,408 ​ Granted ​ 22,777 ​ ​ 6.97 ​ ​ ​ ​ Issued (1) (138,570) ​ ​ 25.86 ​ ​ ​ ​ Phantom units outstanding as of September 30, 2021 644,837 ​ 20.69 ​ ​ 7,009 ​ (1) During the nine months ended September 30, 2021, we issued 102,962 ARLP common units purchased on the open market to a participant under the SERP. Units issued were net of units settled in cash to satisfy tax withholding obligations.

COMPONENTS OF PENSION PLAN NE_2

COMPONENTS OF PENSION PLAN NET PERIODIC BENEFIT COSTS (Tables)	9 Months Ended
	Sep. 30, 2021
Defined benefit pension plan
Employee Benefit Plans
Components of net periodic benefit cost	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Three Months Ended ​ Nine Months Ended ​ ​ ​ September 30, ​ September 30, ​ ​ ​ 2021 2020 2021 2020 ​ ​ (in thousands) ​ Interest cost ​ $ 860 ​ $ 1,030 ​ $ 2,580 ​ $ 3,138 ​ Expected return on plan assets ​ (1,671) ​ (1,413) ​ (5,013) ​ (4,396) ​ Amortization of prior service cost ​ ​ 47 ​ ​ 47 ​ ​ 140 ​ ​ 140 ​ Amortization of net loss ​ 1,141 ​ 969 ​ 3,424 ​ 3,096 ​ Net periodic benefit cost (1) ​ $ 377 ​ $ 633 ​ $ 1,131 ​ $ 1,978 ​ (1) Net periodic benefit cost for the Pension Plan is included in the Other expense line item within our condensed consolidated statements of operations.

SEGMENT INFORMATION (Tables)

SEGMENT INFORMATION (Tables)	9 Months Ended
	Sep. 30, 2021
SEGMENT INFORMATION
Schedule of reportable segment results	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Coal Operations ​ Royalties ​ Other, ​ ​ ​ ​ ​ Illinois ​ ​ ​ ​ ​ Corporate and ​ ​ ​ ​ Basin Appalachia Oil & Gas Coal ​ Elimination Consolidated ​ ​ (in thousands) Three Months Ended September 30, 2021 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Revenues - Outside ​ $ 231,093 ​ $ 154,944 ​ $ 21,191 ​ $ — ​ $ 8,211 ​ $ 415,439 ​ Revenues - Intercompany ​ ​ — ​ ​ — ​ ​ — ​ ​ 13,456 ​ ​ (13,456) ​ ​ — ​ Total revenues (1) ​ ​ 231,093 ​ ​ 154,944 ​ ​ 21,191 ​ ​ 13,456 ​ ​ (5,245) ​ ​ 415,439 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Segment Adjusted EBITDA Expense (2) ​ 149,666 ​ 92,312 ​ 2,639 ​ 4,258 ​ (9,525) ​ 239,350 ​ Segment Adjusted EBITDA (3) ​ 69,305 ​ 52,726 ​ 19,080 ​ 9,198 ​ 4,280 ​ 154,589 ​ Capital expenditures ​ 19,081 ​ 12,531 ​ — ​ 30 ​ 1,393 ​ 33,035 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Three Months Ended September 30, 2020 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Revenues - Outside ​ $ 210,319 ​ $ 132,310 ​ $ 9,721 ​ $ 42 ​ $ 3,259 ​ $ 355,651 ​ Revenues - Intercompany ​ ​ — ​ ​ — ​ ​ — ​ ​ 11,406 ​ ​ (11,406) ​ ​ — ​ Total revenues (1) ​ ​ 210,319 ​ ​ 132,310 ​ ​ 9,721 ​ ​ 11,448 ​ ​ (8,147) ​ ​ 355,651 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Segment Adjusted EBITDA Expense (2) ​ 131,014 ​ 86,701 ​ 849 ​ 5,161 ​ (6,975) ​ 216,750 ​ Segment Adjusted EBITDA (3) ​ 75,583 ​ 43,105 ​ 8,898 ​ 6,287 ​ (1,172) ​ 132,701 ​ Capital expenditures ​ 3,815 ​ 14,541 ​ — ​ — ​ 219 ​ 18,575 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Nine Months Ended September 30, 2021 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Revenues - Outside ​ $ 640,260 ​ $ 384,286 ​ $ 52,798 ​ $ — ​ $ 19,160 ​ $ 1,096,504 ​ Revenues - Intercompany ​ ​ — ​ ​ — ​ ​ — ​ ​ 36,410 ​ ​ (36,410) ​ ​ — ​ Total revenues (1) ​ ​ 640,260 ​ ​ 384,286 ​ ​ 52,798 ​ ​ 36,410 ​ ​ (17,250) ​ ​ 1,096,504 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Segment Adjusted EBITDA Expense (2) ​ 415,423 ​ ​ 240,494 ​ ​ 7,116 ​ ​ 13,157 ​ ​ (24,619) ​ 651,571 ​ Segment Adjusted EBITDA (3) ​ 197,601 ​ ​ 125,873 ​ ​ 46,405 ​ ​ 23,253 ​ ​ 7,370 ​ 400,502 ​ Total assets ​ 703,060 ​ ​ 422,504 ​ ​ 601,695 ​ ​ 289,100 ​ ​ 132,616 ​ 2,148,975 ​ Capital expenditures ​ 47,997 ​ ​ 34,579 ​ ​ — ​ ​ 30 ​ ​ 6,055 ​ 88,661 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Nine Months Ended September 30, 2020 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Revenues - Outside ​ $ 551,978 ​ $ 367,523 ​ $ 31,831 ​ $ 47 ​ $ 10,237 ​ $ 961,616 ​ Revenues - Intercompany ​ ​ — ​ ​ — ​ ​ — ​ ​ 29,555 ​ ​ (29,555) ​ ​ — ​ Total revenues (1) ​ ​ 551,978 ​ ​ 367,523 ​ ​ 31,831 ​ ​ 29,602 ​ ​ (19,318) ​ ​ 961,616 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Segment Adjusted EBITDA Expense (2) ​ 399,664 ​ ​ 240,846 ​ ​ 2,851 ​ ​ 12,649 ​ ​ (17,021) ​ 638,989 ​ Segment Adjusted EBITDA (3) ​ 141,583 ​ ​ 120,686 ​ ​ 29,534 ​ ​ 16,953 ​ ​ (2,298) ​ 306,458 ​ Total assets ​ 799,936 ​ ​ 461,751 ​ ​ 616,491 ​ ​ 291,854 ​ ​ 61,308 ​ 2,231,340 ​ Capital expenditures ​ 44,073 ​ ​ 57,798 ​ ​ — ​ ​ — ​ ​ 949 ​ 102,820 ​ (1) Revenues included in the Other, Corporate and Elimination column are attributable to intercompany eliminations, which are primarily the coal royalties intercompany eliminations, outside revenues at the Matrix Group and other outside miscellaneous sales and revenue activities. ​ (2) Segment Adjusted EBITDA Expense includes operating expenses, coal purchases and other income. Transportation expenses are excluded as transportation revenues are recognized in an amount equal to transportation expenses when title passes to the customer.
Reconciliation of consolidated Segment Adjusted EBITDA Expense to operating expenses (excluding depreciation, depletion and amortization)	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Three Months Ended ​ Nine Months Ended ​ ​ ​ September 30, ​ September 30, ​ ​ ​ 2021 2020 2021 2020 ​ ​ (in thousands) ​ Segment Adjusted EBITDA Expense ​ $ 239,350 ​ $ 216,750 ​ $ 651,571 ​ $ 638,989 ​ Outside coal purchases ​ (6,065) ​ — ​ (6,179) ​ — ​ Other expense ​ (84) ​ (723) ​ (2,632) ​ (1,456) ​ Operating expenses (excluding depreciation, depletion and amortization) ​ $ 233,201 ​ $ 216,027 ​ $ 642,760 ​ $ 637,533 ​ ​ (3) Segment Adjusted EBITDA is defined as net income (loss) attributable to ARLP before net interest expense, income taxes, depreciation, depletion and amortization, general and administrative expenses and asset and goodwill impairments. Management therefore is able to focus solely on the evaluation of segment operating profitability as it relates to our revenues and operating expenses, which are primarily controlled by our segments. Consolidated Segment Adjusted EBITDA is reconciled to net income as follows:
Reconciliation of consolidated Segment Adjusted EBITDA to net income	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Three Months Ended ​ Nine Months Ended ​ ​ ​ September 30, ​ September 30, ​ ​ ​ 2021 2020 2021 2020 ​ ​ (in thousands) ​ Consolidated Segment Adjusted EBITDA ​ $ 154,589 ​ $ 132,701 ​ $ 400,502 ​ $ 306,458 ​ General and administrative ​ (18,655) ​ (13,871) ​ (51,651) ​ (41,131) ​ Depreciation, depletion and amortization ​ (68,763) ​ (80,182) ​ (192,698) ​ (237,662) ​ Asset impairments ​ — ​ — ​ — ​ (24,977) ​ Goodwill impairment ​ ​ — ​ ​ — ​ ​ — ​ ​ (132,026) ​ Interest expense, net ​ (9,389) ​ (11,156) ​ (29,595) ​ (34,799) ​ Income tax expense ​ (234) ​ (293) ​ (227) ​ (111) ​ Net income (loss) attributable to ARLP ​ $ 57,548 ​ $ 27,199 ​ $ 126,331 ​ $ (164,248) ​ Noncontrolling interest ​ ​ 176 ​ ​ 36 ​ ​ 384 ​ ​ 97 ​ Net income (loss) ​ $ 57,724 ​ $ 27,235 ​ $ 126,715 ​ $ (164,151) ​

LONG-LIVED ASSET IMPAIRMENTS (D

LONG-LIVED ASSET IMPAIRMENTS (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
	Mar. 31, 2020	Sep. 30, 2020
Asset impairment charges
Asset impairments		$ 24,977
Illinois Basin
Asset impairment charges
Asset impairments	$ 23,500
Coal Royalties
Asset impairment charges
Asset impairments	$ 1,500

GOODWILL IMPAIRMENT (Details)

GOODWILL IMPAIRMENT (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
	Mar. 31, 2020	Sep. 30, 2020	Sep. 30, 2021	Dec. 31, 2020	Dec. 31, 2019
GOODWILL IMPAIRMENT
Goodwill	$ 4,400		$ 4,373	$ 4,373	$ 136,400
Impairments of goodwill		$ 132,026
Hamilton mining complex
GOODWILL IMPAIRMENT
Goodwill					$ 132,000
Impairments of goodwill	$ 132,000

INVENTORIES (Details)

INVENTORIES (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
INVENTORIES
Coal	$ 31,066	$ 19,756
Supplies (net of reserve for obsolescence of $5,554 and $5,547, respectively)	34,418	36,651
Total inventories, net	65,484	56,407
Reserve for obsolescence	$ 5,554	$ 5,547

FAIR VALUE MEASUREMENTS (Detail

FAIR VALUE MEASUREMENTS (Details) - Estimated fair value - Significant Observable Inputs (Level 2) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
FAIR VALUE MEASUREMENTS
Long-term debt	$ 459,650	$ 518,317
Total	$ 459,650	$ 518,317

LONG-TERM DEBT - Components (De

LONG-TERM DEBT - Components (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Principal
Aggregate maturities of long-term debt	$ 450,722	$ 603,780
Less current maturities	(16,770)	(73,199)
Total long-term debt	433,952	530,581
Unamortized Discount and Debt Issuance Costs
Unamortized debt issuance costs including current and non-current	(8,877)	(11,160)
Total unamortized debt issuance costs	(8,877)	(11,160)
Revolving credit facility
Principal
Aggregate maturities of long-term debt		87,500
Unamortized Discount and Debt Issuance Costs
Unamortized debt issuance costs including current and non-current	(5,599)	(7,196)
Senior notes due 2025
Principal
Aggregate maturities of long-term debt	400,000	400,000
Unamortized Discount and Debt Issuance Costs
Unamortized debt issuance costs including current and non-current	(3,278)	(3,964)
Securitization Facility
Principal
Aggregate maturities of long-term debt		55,900
May 2019 equipment financing
Principal
Aggregate maturities of long-term debt	2,387	4,956
November 2019 equipment financing
Principal
Aggregate maturities of long-term debt	34,617	42,367
June 2020 equipment financing
Principal
Aggregate maturities of long-term debt	10,488	$ 13,057
Line of credit
Principal
Aggregate maturities of long-term debt	$ 3,230

LONG-TERM DEBT - Credit Facilit

LONG-TERM DEBT - Credit Facility (Details) $ in Millions	Mar. 09, 2020USD ($)	Sep. 30, 2021USD ($)
Credit Agreement
Long-Term Debt
Maximum borrowing capacity	$ 459.5
ARLP debt arrangements requirements, fixed charge coverage ratio	1
ARLP debt arrangements requirements, debt to cash flow ratio	2.5
ARLP debt arrangements requirements, cash flow to interest expense ratio	3
Actual debt to cash flow ratio for trailing twelve months		0.95
Actual cash flow to interest expense ratio for trailing twelve months		11.60
ARLP debt arrangements requirements, period over which the ratios are required to be maintained	12 months
Credit Agreement | Credit Agreement, first lien
Long-Term Debt
ARLP debt arrangements requirements, debt to cash flow ratio	1.5
Actual debt to cash flow ratio for trailing twelve months		0.10
Revolving credit facility
Long-Term Debt
Line of credit facility, available for borrowing		$ 436.2
Annual commitment fee percentage, undrawn portion		0.35%
Revolving credit facility | Eurodollar Rate
Long-Term Debt
Effective interest rate (as a percent)		2.68%
Letters of credit subfacility
Long-Term Debt
Maximum borrowing capacity	$ 125
Letters of credit outstanding		$ 23.3
Swingline subfacility
Long-Term Debt
Maximum borrowing capacity	$ 15

LONG-TERM DEBT - 2025 Senior No

LONG-TERM DEBT - 2025 Senior Notes (Details) - Senior notes due 2025 $ in Millions	Apr. 24, 2017USD ($)
Issuance of Senior Notes
Principal amount	$ 400
Term	8 years
Interest rate (as a percent)	7.50%

LONG-TERM DEBT - Securitization

LONG-TERM DEBT - Securitization Facility (Details) - Securitization Facility - USD ($) $ in Millions	Sep. 30, 2021	Jan. 31, 2021	Dec. 05, 2014
Long-Term Debt
Maximum borrowing capacity		$ 60	$ 100
Facility outstanding amount	$ 0

LONG-TERM DEBT - Equipment fina

LONG-TERM DEBT - Equipment financing and other (Details) $ in Millions	Jun. 05, 2020USD ($)	Nov. 06, 2019USD ($)payment	May 17, 2019USD ($)
May 2019 Equipment Financing
Long-Term Debt
Principal amount			$ 10
Term			36 months
Effective interest rate (as a percent)			6.25%
November 2019 Equipment Financing
Long-Term Debt
Principal amount		$ 53.1
Term		4 years
Effective interest rate (as a percent)		4.75%
Number of monthly payments | payment		47
Periodic Payment		$ 1
Balloon payment on maturity		$ 11.6
June 2020 equipment financing
Long-Term Debt
Principal amount	$ 14.7
Term	48 months
Effective interest rate (as a percent)	6.10%

LONG-TERM DEBT - Line of Credit

LONG-TERM DEBT - Line of Credit (Details) - Line of credit - USD ($) $ in Millions	Feb. 19, 2021	Sep. 30, 2021
Long-Term Debt
Maximum borrowing capacity	$ 5
Extension term	6 months
Interest rate (as a percent)	3.50%
Facility outstanding amount		$ 3.2

VARIABLE INTEREST ENTITIES - Ca

VARIABLE INTEREST ENTITIES - Cavalier (Details) - USD ($) $ in Thousands	Aug. 13, 2021	May 14, 2021	Feb. 14, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Variable Interest Entities
Distributions paid to Partners	$ 13,041	$ 13,045	$ 51,753	$ 26,086	$ 51,753	$ 51,753
Cavalier Minerals | Alliance Minerals
Variable Interest Entities
Contributions				143,112
Distributions paid to Partners				104,149
Cavalier Minerals | Bluegrass Minerals
Variable Interest Entities
Contributions				5,963
Distributions paid to Partners				$ 4,339
Cavalier Minerals | Bluegrass Minerals
Variable Interest Entities
Incentive distribution of available cash (as a percent)				25.00%
Cavalier Minerals
Variable Interest Entities
Ownership interest in VIE (as a percent)				96.00%
Cavalier Minerals | Bluegrass Minerals
Variable Interest Entities
Noncontrolling ownership interest (as a percent)				4.00%

VARIABLE INTEREST ENTITIES - Al

VARIABLE INTEREST ENTITIES - All Dale III (Detail) - All Dale Minerals III - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2021	Feb. 28, 2017
Equity Investments
Other Commitment		$ 30
Distribution after hurdles (as a percent)	25.00%
Specified internal rate of return (as a percent)	10.00%
Percentage of available cash distributed	125.00%
All Dale Minerals III
Equity Investments
Ownership percentage by limited partners	13.90%

INVESTMENT - AllDale (Details)

INVESTMENT - AllDale (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
ASSETS
Beginning balance			$ 27,268
Equity method investment income	$ 703	$ 62	1,106	$ 650
Ending balance	26,180		26,180
All Dale Minerals III
ASSETS
Beginning balance	26,274	27,705	27,268	28,529
Equity method investment income	703	62	1,106	650
Distributions received	(797)	(352)	(2,194)	(1,491)
Other				(273)
Ending balance	$ 26,180	$ 27,415	$ 26,180	$ 27,415

PARTNERS' CAPITAL - Distributio

PARTNERS' CAPITAL - Distributions (Details) - USD ($) $ / shares in Units, $ in Thousands	Nov. 12, 2021	Aug. 13, 2021	May 14, 2021	Feb. 14, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
PARTNERS' CAPITAL
Quarterly distribution paid (in dollars per unit)	$ 0.2000	$ 0.1000	$ 0.1000	$ 0.4000	$ 0.4000		$ 0.4000
Total Cash Distribution		$ 13,041	$ 13,045	$ 51,753	$ 26,086	$ 51,753	$ 51,753

PARTNERS' CAPITAL - Narrative (

PARTNERS' CAPITAL - Narrative (Details) - USD ($) $ / shares in Units, $ in Millions	9 Months Ended	41 Months Ended
	Sep. 30, 2021	Sep. 30, 2021	May 31, 2018
Partners' capital
Treasury units retired	$ 0
Limited Partners' Capital
Partners' capital
Repurchase and retire authorization			$ 100
Treasury units retired		$ 93.5
Number of units retired		5,460,639
Repurchase price (in dollars per unit)		$ 17.12
Remaining authorized amount	$ 6.5	$ 6.5

PARTNERS' CAPITAL - Change (Det

PARTNERS' CAPITAL - Change (Details) - USD ($) $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2021	Sep. 30, 2020
Increase (decrease) in Partners' Capital
Balance at beginning of period	$ 1,134,520	$ 1,099,906	$ 1,072,267	$ 1,023,152	$ 1,067,504	$ 1,265,424	$ 1,072,267	$ 1,265,424
Balance at beginning of period (in units)			127,195,219				127,195,219
Comprehensive income (loss):
Net income (loss)	57,724	44,165	$ 24,826	27,235	(46,679)	(144,707)	$ 126,715	(164,151)
Actuarially determined long-term liability adjustments	2,231	2,231	2,231	844	939	938	6,693	2,721
COMPREHENSIVE INCOME (LOSS)	59,955	46,396	27,057	28,079	(45,740)	(143,769)	133,408	(161,430)
Settlement of deferred compensation plans	(1,090)					(1,310)
Common unit-based compensation	1,746	1,485	723	1,645	1,610	(527)
Distributions on deferred common unit-based compensation	(323)	(324)				(986)
Distributions from consolidated company to noncontrolling interest	(252)	(222)	(141)	(93)	(222)	(288)
Distributions to Partners	(12,718)	(12,721)				(50,767)
Other						(273)
Balance at end of period	$ 1,181,838	1,134,520	1,099,906	1,052,783	1,023,152	1,067,504	$ 1,181,838	1,052,783
Balance at end of period (in units)	127,195,219						127,195,219
Accumulated Other Comprehensive Income (Loss)
Increase (decrease) in Partners' Capital
Balance at beginning of period	$ (83,212)	(85,443)	(87,674)	(76,116)	(77,055)	(77,993)	$ (87,674)	(77,993)
Comprehensive income (loss):
Actuarially determined long-term liability adjustments	2,231	2,231	2,231	844	939	938
Balance at end of period	(80,981)	(83,212)	(85,443)	(75,272)	(76,116)	(77,055)	(80,981)	(75,272)
Noncontrolling Interest
Increase (decrease) in Partners' Capital
Balance at beginning of period	11,221	11,313	11,376	11,486	11,723	11,935	11,376	11,935
Comprehensive income (loss):
Net income (loss)	176	130	78	36	(15)	76
Distributions from consolidated company to noncontrolling interest	(252)	(222)	(141)	(93)	(222)	(288)
Balance at end of period	11,145	11,221	11,313	11,429	11,486	11,723	11,145	11,429
Limited Partners' Capital
Increase (decrease) in Partners' Capital
Balance at beginning of period	$ 1,206,511	$ 1,174,036	$ 1,148,565	$ 1,087,782	$ 1,132,836	$ 1,331,482	$ 1,148,565	$ 1,331,482
Balance at beginning of period (in units)	127,195,219	127,195,219	127,195,219	127,195,219	127,195,219	126,915,597	127,195,219	126,915,597
Comprehensive income (loss):
Net income (loss)	$ 57,548	$ 44,035	$ 24,748	$ 27,199	$ (46,664)	$ (144,783)
Settlement of deferred compensation plans	(1,090)					$ (1,310)
Settlement of deferred compensation plans (in units)						279,622
Common unit-based compensation	1,746	1,485	723	1,645	1,610	$ (527)
Distributions on deferred common unit-based compensation	(323)	(324)				(986)
Distributions to Partners	(12,718)	(12,721)				(50,767)
Other						(273)
Balance at end of period	$ 1,251,674	$ 1,206,511	$ 1,174,036	$ 1,116,626	$ 1,087,782	$ 1,132,836	$ 1,251,674	$ 1,116,626
Balance at end of period (in units)	127,195,219	127,195,219	127,195,219	127,195,219	127,195,219	127,195,219	127,195,219	127,195,219

REVENUE FROM CONTRACTS WITH C_3

REVENUE FROM CONTRACTS WITH CUSTOMERS - Disaggregation (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Disaggregation of revenues
Revenues	$ 415,439	$ 355,651	$ 1,096,504	$ 961,616
Illinois Basin
Disaggregation of revenues
Revenues	231,093	210,319	640,260	551,978
Appalachia
Disaggregation of revenues
Revenues	154,944	132,310	384,286	367,523
Oil & Gas Royalties
Disaggregation of revenues
Revenues	21,191	9,721	52,798	31,831
Coal Royalties
Disaggregation of revenues
Revenues	13,456	11,448	36,410	29,602
Other and Corporate
Disaggregation of revenues
Revenues	(5,245)	(8,147)	(17,250)	(19,318)
Operating segments
Disaggregation of revenues
Revenues	415,439	355,651	1,096,504	961,616
Operating segments | Illinois Basin
Disaggregation of revenues
Revenues	231,093	210,319	640,260	551,978
Operating segments | Appalachia
Disaggregation of revenues
Revenues	154,944	132,310	384,286	367,523
Operating segments | Oil & Gas Royalties
Disaggregation of revenues
Revenues	21,191	9,721	52,798	31,831
Operating segments | Coal Royalties
Disaggregation of revenues
Revenues		42		47
Elimination | Coal Royalties
Disaggregation of revenues
Revenues	13,456	11,406	36,410	29,555
Coal sales
Disaggregation of revenues
Revenues	362,264	335,767	975,725	886,690
Coal sales | Illinois Basin
Disaggregation of revenues
Revenues	217,637	206,356	610,435	539,614
Coal sales | Appalachia
Disaggregation of revenues
Revenues	144,627	129,411	365,290	347,076
Coal royalties | Coal Royalties
Disaggregation of revenues
Revenues	13,456	11,406	36,410	29,555
Coal royalties | Other and Corporate
Disaggregation of revenues
Revenues	(13,456)	(11,406)	(36,410)	(29,555)
Oil & gas royalties
Disaggregation of revenues
Revenues	20,109	9,693	51,222	31,718
Oil & gas royalties | Oil & Gas Royalties
Disaggregation of revenues
Revenues	20,109	9,693	51,222	31,718
Transportation
Disaggregation of revenues
Revenues	22,027	6,226	45,153	16,722
Transportation | Illinois Basin
Disaggregation of revenues
Revenues	12,121	3,722	27,235	10,731
Transportation | Appalachia
Disaggregation of revenues
Revenues	9,906	2,504	17,918	5,991
Other revenues
Disaggregation of revenues
Revenues	11,039	3,965	24,404	26,486
Other revenues | Illinois Basin
Disaggregation of revenues
Revenues	1,335	241	2,590	1,633
Other revenues | Appalachia
Disaggregation of revenues
Revenues	411	395	1,078	14,456
Other revenues | Oil & Gas Royalties
Disaggregation of revenues
Revenues	1,082	28	1,576	113
Other revenues | Coal Royalties
Disaggregation of revenues
Revenues		42		47
Other revenues | Other and Corporate
Disaggregation of revenues
Revenues	$ 8,211	$ 3,259	$ 19,160	$ 10,237

REVENUE FROM CONTRACTS WITH C_4

REVENUE FROM CONTRACTS WITH CUSTOMERS - Supply contracts (Details) $ in Thousands	Sep. 30, 2021USD ($)
Performance obligations unsatisfied or partially unsatisfied
Total	$ 1,850,369
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2021-10-01
Performance obligations unsatisfied or partially unsatisfied
Total	$ 476,711
Expected timing of satisfaction period	3 months
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2022-01-01
Performance obligations unsatisfied or partially unsatisfied
Total	$ 893,545
Expected timing of satisfaction period	1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2023-01-01
Performance obligations unsatisfied or partially unsatisfied
Total	$ 273,350
Expected timing of satisfaction period	1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2024-01-01
Performance obligations unsatisfied or partially unsatisfied
Total	$ 206,763
Expected timing of satisfaction period	1 year
Illinois Basin
Performance obligations unsatisfied or partially unsatisfied
Total	$ 1,313,503
Illinois Basin | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2021-10-01
Performance obligations unsatisfied or partially unsatisfied
Total	$ 293,651
Expected timing of satisfaction period	3 months
Illinois Basin | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2022-01-01
Performance obligations unsatisfied or partially unsatisfied
Total	$ 567,699
Expected timing of satisfaction period	1 year
Illinois Basin | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2023-01-01
Performance obligations unsatisfied or partially unsatisfied
Total	$ 255,470
Expected timing of satisfaction period	1 year
Illinois Basin | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2024-01-01
Performance obligations unsatisfied or partially unsatisfied
Total	$ 196,683
Expected timing of satisfaction period	1 year
Appalachia
Performance obligations unsatisfied or partially unsatisfied
Total	$ 536,866
Appalachia | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2021-10-01
Performance obligations unsatisfied or partially unsatisfied
Total	$ 183,060
Expected timing of satisfaction period	3 months
Appalachia | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2022-01-01
Performance obligations unsatisfied or partially unsatisfied
Total	$ 325,846
Expected timing of satisfaction period	1 year
Appalachia | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2023-01-01
Performance obligations unsatisfied or partially unsatisfied
Total	$ 17,880
Expected timing of satisfaction period	1 year
Appalachia | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2024-01-01
Performance obligations unsatisfied or partially unsatisfied
Total	$ 10,080
Expected timing of satisfaction period	1 year

EARNINGS PER LIMITED PARTNER _3

EARNINGS PER LIMITED PARTNER UNIT - Reconciliation (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
EARNINGS PER LIMITED PARTNER UNIT
Net income (loss) attributable to ARLP	$ 57,548	$ 27,199	$ 126,331	$ (164,248)
Distributions to participating securities	(765)		(1,384)
Undistributed earnings attributable to participating securities	(951)	(581)	(1,832)
Net income (loss) attributable to ARLP available to limited partners	$ 55,832	$ 26,618	$ 123,115	$ (164,248)
Weighted-average limited partner units outstanding - basic and diluted	127,195,219	127,195,219	127,195,219	127,154,398
Earnings per limited partner unit - basic and diluted	$ 0.44	$ 0.21	$ 0.97	$ (1.29)
Anti-dilutive under the treasury stock method (in units)	2,328,000	661,000	1,706,000	656,000

WORKERS' COMPENSATION AND PNE_3

WORKERS' COMPENSATION AND PNEUMOCONIOSIS - Liability (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020	Dec. 31, 2019
Reconciliation of changes in the workers' compensation liability
Beginning balance	$ 52,059	$ 54,478	$ 54,739	$ 53,384	$ 54,739	$ 53,384	$ 53,384
Accruals increase	1,674	1,599			4,911	3,539
Payments	(2,939)	(2,123)			(7,914)	(6,686)
Interest accretion	232	319			695	958
Valuation loss (gain)					(1,405)	3,078
Ending balance	51,026	$ 54,273	$ 52,059	$ 54,478	51,026	$ 54,273	$ 54,739	$ 53,384
Workers' compensation discount rate			2.34%	2.05%			1.95%	2.81%
Receivables for traumatic injury claims	$ 7,100				$ 7,100

WORKERS' COMPENSATION AND PNE_4

WORKERS' COMPENSATION AND PNEUMOCONIOSIS - Periodic Benefit Cost (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Accrued Workers Compensation And Pneumoconiosis Benefits
Interest cost	$ 860	$ 1,030	$ 2,580	$ 3,138
Net amortization	1,141	969	3,424	3,096
Net periodic benefit cost	377	633	1,131	1,978
Pneumoconiosis benefits
Accrued Workers Compensation And Pneumoconiosis Benefits
Service cost	1,007	882	3,027	2,643
Interest cost	636	750	1,909	2,249
Net amortization	1,043	(172)	3,129	(515)
Net periodic benefit cost	$ 2,686	$ 1,460	$ 8,065	$ 4,377

COMMON UNIT-BASED COMPENSATIO_3

COMMON UNIT-BASED COMPENSATION PLANS - LTIP Grants (Details) - USD ($) $ / shares in Units, $ in Thousands	9 Months Ended
	Sep. 30, 2021	Dec. 31, 2020
Number of units
Balance at the beginning of the period (in units)	1,430,489
Granted (in units)	1,818,190
Forfeited (in units)	(69,933)
Balance at the end of the period (in units)	3,178,746
Weighted average grant date fair value per unit
Balance at the beginning of the period (in dollars per unit)	$ 5.02
Granted (in dollars per unit)	6.03
Forfeited (in dollars per unit)	5.46
Balance at the end of the period (in dollars per unit)	$ 5.59
Intrinsic value (in dollars)
Intrinsic value of outstanding grants (in dollars)	$ 34,553	$ 6,409
$2.53 minimum-value guarantee
Other information
Guaranteed minimum (in shares)	921,430
Guaranteed minimum (in dollars per unit)	$ 2.53
$3.79 minimum-value guarantee
Other information
Guaranteed minimum (in shares)	896,760
Guaranteed minimum (in dollars per unit)	$ 3.79

COMMON UNIT-BASED COMPENSATIO_4

COMMON UNIT-BASED COMPENSATION PLANS - LTIP Other (Details) - ARLP LTIP - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Other information
Unit-based compensation expense	$ 1.7	$ 1.6	$ 3.8	$ 2.5
Reversal of cumulative previously recognized expenses				$ 4.8
Total unit-based obligation recorded	5.1		5.1
Unrecognized compensation expense (in dollars)	$ 12.6		$ 12.6
Weighted-average period for recognition of expense			1 year 9 months 18 days

COMMON UNIT-BASED COMPENSATIO_5

COMMON UNIT-BASED COMPENSATION PLANS - SERP and Directors Comp (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Weighted average grant date fair value per unit
Granted (in dollars per unit)			$ 6.03
Intrinsic value of outstanding grants (in dollars)	$ 34,553		$ 34,553		$ 6,409
SERP and Deferred Compensation Plans
Number of units
Balance at the beginning of the period (in units)			760,630
Granted (in units)			22,777
Issued (in units)			(138,570)
Balance at the end of the period (in units)	644,837		644,837
Other information
Common units issued			102,962
Unit-based compensation expense	$ 100	$ 100	$ 300	$ 400
Total unit-based obligation recorded	$ 13,300		$ 13,300
SERP and Deferred Compensation Plans | Phantom Share Units (PSUs)
Weighted average grant date fair value per unit
Balance at the beginning of the period (in dollars per unit)			$ 22.04
Granted (in dollars per unit)			6.97
Issued (in dollars per unit)			25.86
Balance at the end of the period (in dollars per unit)	$ 20.69		$ 20.69
Intrinsic value of outstanding grants (in dollars)	$ 7,009		$ 7,009		$ 3,408

COMPONENTS OF PENSION PLAN NE_3

COMPONENTS OF PENSION PLAN NET PERIODIC BENEFIT COSTS (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Components of net periodic benefit cost:
Interest cost	$ 860	$ 1,030	$ 2,580	$ 3,138
Expected return on plan assets	(1,671)	(1,413)	(5,013)	(4,396)
Amortization of prior service cost	47	47	140	140
Amortization of net loss	1,141	969	3,424	3,096
Net periodic benefit cost	$ 377	$ 633	1,131	$ 1,978
2020 plan year
Components of net periodic benefit cost:
Employer contribution			$ 3,300

SEGMENT INFORMATION - Segment R

SEGMENT INFORMATION - Segment Results (Details) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021USD ($)	Sep. 30, 2020USD ($)	Sep. 30, 2021USD ($)segment	Sep. 30, 2020USD ($)	Dec. 31, 2020USD ($)
Segment Information
Number of reportable segments | segment			4
Reportable segment results
Revenues	$ 415,439	$ 355,651	$ 1,096,504	$ 961,616
Segment Adjusted EBITDA Expense	239,350	216,750	651,571	638,989
Segment Adjusted EBITDA	154,589	132,701	400,502	306,458
Total assets	2,148,975	2,231,340	2,148,975	2,231,340	$ 2,166,016
Capital expenditures	33,035	18,575	$ 88,661	102,820
Coal Operations
Segment Information
Number of reportable segments | segment			2
Number of mining complex | segment			7
Illinois Basin
Reportable segment results
Revenues	231,093	210,319	$ 640,260	551,978
Segment Adjusted EBITDA Expense	149,666	131,014	415,423	399,664
Segment Adjusted EBITDA	69,305	75,583	197,601	141,583
Total assets	703,060	799,936	703,060	799,936
Capital expenditures	19,081	3,815	47,997	44,073
Appalachia
Reportable segment results
Revenues	154,944	132,310	384,286	367,523
Segment Adjusted EBITDA Expense	92,312	86,701	240,494	240,846
Segment Adjusted EBITDA	52,726	43,105	125,873	120,686
Total assets	422,504	461,751	422,504	461,751
Capital expenditures	12,531	14,541	34,579	57,798
Oil & Gas Royalties
Reportable segment results
Revenues	21,191	9,721	52,798	31,831
Segment Adjusted EBITDA Expense	2,639	849	7,116	2,851
Segment Adjusted EBITDA	19,080	8,898	46,405	29,534
Total assets	601,695	616,491	601,695	616,491
Coal Royalties
Reportable segment results
Revenues	13,456	11,448	36,410	29,602
Segment Adjusted EBITDA Expense	4,258	5,161	13,157	12,649
Segment Adjusted EBITDA	9,198	6,287	23,253	16,953
Total assets	289,100	291,854	289,100	291,854
Capital expenditures	30		30
Other and Corporate and Elimination
Reportable segment results
Revenues	(5,245)	(8,147)	(17,250)	(19,318)
Segment Adjusted EBITDA Expense	(9,525)	(6,975)	(24,619)	(17,021)
Segment Adjusted EBITDA	4,280	(1,172)	7,370	(2,298)
Total assets	132,616	61,308	132,616	61,308
Capital expenditures	1,393	219	6,055	949
Operating segments
Reportable segment results
Revenues	415,439	355,651	1,096,504	961,616
Operating segments | Illinois Basin
Reportable segment results
Revenues	231,093	210,319	640,260	551,978
Operating segments | Appalachia
Reportable segment results
Revenues	154,944	132,310	384,286	367,523
Operating segments | Oil & Gas Royalties
Reportable segment results
Revenues	21,191	9,721	52,798	31,831
Operating segments | Coal Royalties
Reportable segment results
Revenues		42		47
Operating segments | Other and Corporate and Elimination
Reportable segment results
Revenues	8,211	3,259	19,160	10,237
Elimination | Coal Royalties
Reportable segment results
Revenues	13,456	11,406	36,410	29,555
Elimination | Other and Corporate and Elimination
Reportable segment results
Revenues	$ (13,456)	$ (11,406)	$ (36,410)	$ (29,555)

SEGMENT INFORMATION - EBITDA Ex

SEGMENT INFORMATION - EBITDA Expense Reconciliation (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Reconciliation of consolidated Segment Adjusted EBITDA Expense
Segment Adjusted EBITDA Expense	$ 239,350	$ 216,750	$ 651,571	$ 638,989
Outside coal purchases	(6,065)		(6,179)
Other expense	(84)	(723)	(2,632)	(1,456)
Product
Reconciliation of consolidated Segment Adjusted EBITDA Expense
Operating expenses (excluding depreciation, depletion and amortization)	$ 233,201	$ 216,027	$ 642,760	$ 637,533

SEGMENT INFORMATION - EBITDA Re

SEGMENT INFORMATION - EBITDA Reconciliation (Details) - USD ($) $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2021	Sep. 30, 2020
Reconciliation of consolidated Segment Adjusted EBITDA to net income
Consolidated Segment Adjusted EBITDA	$ 154,589			$ 132,701			$ 400,502	$ 306,458
General and administrative	(18,655)			(13,871)			(51,651)	(41,131)
Depreciation, depletion and amortization	(68,763)			(80,182)			(192,698)	(237,662)
Asset impairment								(24,977)
Goodwill impairment								(132,026)
Interest expense, net	(9,389)			(11,156)			(29,595)	(34,799)
Income tax (expense) benefit	(234)			(293)			(227)	(111)
NET INCOME (LOSS) ATTRIBUTABLE TO ARLP	57,548			27,199			126,331	(164,248)
Noncontrolling interest	176			36			384	97
NET INCOME (LOSS)	$ 57,724	$ 44,165	$ 24,826	$ 27,235	$ (46,679)	$ (144,707)	$ 126,715	$ (164,151)

SUBSEQUENT EVENTS (Details)

SUBSEQUENT EVENTS (Details) - Subsequent event $ in Millions	Oct. 13, 2021USD ($)a
Subsequent Event
Royalty acres, net | a	1,480
Oil & gas royalty acquisition | $	$ 31