Alliance Resource Partners (ARLP) 10-Q 5 Nov 20 2020 Q3 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	9 Months Ended
	Sep. 30, 2020	Nov. 05, 2020
Document and Entity Information
Document Type	10-Q
Document Quarterly Report	true
Document Transition Report	false
Document Period End Date	Sep. 30, 2020
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	Large 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	2020
Document Fiscal Period Focus	Q3
Amendment Flag	false

CONDENSED CONSOLIDATED BALANCE

CONDENSED CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
CURRENT ASSETS:
Cash and cash equivalents	$ 34,135	$ 36,482
Trade receivables	120,875	161,679
Other receivables	1,919	256
Inventories, net	74,879	101,305
Advance royalties	344	1,844
Prepaid expenses and other assets	10,984	18,019
Total current assets	243,136	319,585
PROPERTY, PLANT AND EQUIPMENT:
Property, plant and equipment, at cost	3,619,568	3,684,008
Less accumulated depreciation, depletion and amortization	(1,758,646)	(1,675,022)
Total property, plant and equipment, net	1,860,922	2,008,986
OTHER ASSETS:
Advance royalties	59,850	52,057
Equity method investments	27,415	28,529
Goodwill	4,373	136,399
Operating lease right-of-use assets	15,388	17,660
Other long-term assets	20,256	23,478
Total other assets	127,282	258,123
TOTAL ASSETS	2,231,340	2,586,694
CURRENT LIABILITIES:
Accounts payable	54,789	80,566
Accrued taxes other than income taxes	17,397	15,768
Accrued payroll and related expenses	41,667	36,575
Accrued interest	12,691	5,664
Workers' compensation and pneumoconiosis benefits	11,162	11,175
Current finance lease obligations	732	8,368
Current operating lease obligations	1,863	3,251
Other current liabilities	23,803	21,062
Current maturities, long-term debt, net	89,271	13,157
Total current liabilities	253,375	195,586
LONG-TERM LIABILITIES:
Long-term debt, excluding current maturities, net	571,019	768,194
Pneumoconiosis benefits	96,906	94,389
Accrued pension benefit	41,862	44,858
Workers' compensation	46,404	45,503
Asset retirement obligations	132,627	133,018
Long-term finance lease obligations	1,656	2,224
Long-term operating lease obligations	13,599	14,316
Other liabilities	21,109	23,182
Total long-term liabilities	925,182	1,125,684
Total liabilities	1,178,557	1,321,270
ARLP Partners' Capital:
Limited Partners - Common Unitholders 127,195,219 and 126,915,597 units outstanding, respectively	1,116,626	1,331,482
Accumulated other comprehensive loss	(75,272)	(77,993)
Total ARLP Partners' Capital	1,041,354	1,253,489
Noncontrolling interest	11,429	11,935
Total Partners' Capital	1,052,783	1,265,424
TOTAL LIABILITIES AND PARTNERS' CAPITAL	$ 2,231,340	$ 2,586,694

CONDENSED CONSOLIDATED BALANC_2

CONDENSED CONSOLIDATED BALANCE SHEETS (Parenthetical) - shares	Sep. 30, 2020	Dec. 31, 2019
CONDENSED CONSOLIDATED BALANCE SHEETS
Common units outstanding	127,195,219	126,915,597

CONDENSED CONSOLIDATED STATEMEN

CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
SALES AND OPERATING REVENUES:
Revenues	$ 355,651	$ 464,726	$ 961,616	$ 1,508,382
EXPENSES:
Operating expenses (excluding depreciation, depletion and amortization)	216,027	278,254	637,533	895,255
Outside coal purchases		10,599		15,910
General and administrative	13,871	17,885	41,131	55,218
Depreciation, depletion and amortization	80,182	72,348	237,662	220,400
Asset impairments		15,190	24,977	15,190
Goodwill impairment			132,026
Total operating expenses	316,306	414,300	1,090,051	1,284,865
INCOME (LOSS) FROM OPERATIONS	39,345	50,426	(128,435)	223,517
Interest expense (net of interest capitalized for the three and nine months ended September 30, 2020 and 2019 of $199, $298, $1,265 and $790, respectively)	(11,186)	(11,698)	(34,911)	(33,831)
Interest income	30	92	112	321
Equity method investment income	62	659	650	1,533
Equity securities income				12,906
Acquisition gain				177,043
Other expense	(723)	(228)	(1,456)	(370)
INCOME (LOSS) BEFORE INCOME TAXES	27,528	39,251	(164,040)	381,119
INCOME TAX EXPENSE	293	50	111	130
NET INCOME (LOSS)	27,235	39,201	(164,151)	380,989
LESS: NET INCOME ATTRIBUTABLE TO NONCONTROLLING INTEREST	(36)	(117)	(97)	(7,407)
NET INCOME (LOSS) ATTRIBUTABLE TO ARLP	$ 27,199	$ 39,084	$ (164,248)	$ 373,582
EARNINGS PER LIMITED PARTNER UNIT - BASIC AND DILUTED	$ 0.21	$ 0.30	$ (1.29)	$ 2.86
WEIGHTED-AVERAGE NUMBER OF UNITS OUTSTANDING - BASIC AND DILUTED	127,195,219	128,391,191	127,154,398	128,311,609
Coal sales
SALES AND OPERATING REVENUES:
Revenues	$ 335,767	$ 420,005	$ 886,690	$ 1,357,331
EXPENSES:
Operating expenses (excluding depreciation, depletion and amortization)	216,027	278,254	637,533	895,255
Oil & gas royalties
SALES AND OPERATING REVENUES:
Revenues	9,693	13,969	31,718	36,254
Transportation revenues
SALES AND OPERATING REVENUES:
Revenues	6,226	20,024	16,722	82,892
EXPENSES:
Transportation expenses	6,226	20,024	16,722	82,892
Other revenues
SALES AND OPERATING REVENUES:
Revenues	$ 3,965	$ 10,728	$ 26,486	$ 31,905

CONDENSED CONSOLIDATED STATEM_2

CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS (Parenthetical) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS
Interest expense, interest capitalized	$ 199	$ 298	$ 1,265	$ 790

CONDENSED CONSOLIDATED STATEM_3

CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (LOSS) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
NET INCOME (LOSS)	$ 27,235	$ 39,201	$ (164,151)	$ 380,989
OTHER COMPREHENSIVE INCOME (LOSS):
OTHER COMPREHENSIVE INCOME (LOSS)	844	(119)	2,721	(3,821)
COMPREHENSIVE INCOME (LOSS)	28,079	39,082	(161,430)	377,168
Less: Comprehensive income attributable to noncontrolling interest	(36)	(117)	(97)	(7,407)
COMPREHENSIVE INCOME (LOSS) ATTRIBUTABLE TO ARLP	28,043	38,965	(161,527)	369,761
Defined benefit pension plan
OTHER COMPREHENSIVE INCOME (LOSS):
Amortization of prior service cost	47	46	140	139
Amortization of net actuarial gain loss	969	980	3,096	2,941
Total adjustments	1,016	1,026	3,236	3,080
Pneumoconiosis benefits
OTHER COMPREHENSIVE INCOME (LOSS):
Net actuarial loss				(3,465)
Amortization of net actuarial gain loss	(172)	(1,145)	(515)	(3,436)
Total adjustments	$ (172)	$ (1,145)	$ (515)	$ (6,901)

CONDENSED CONSOLIDATED STATEM_4

CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	9 Months Ended		12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS
CASH FLOWS FROM OPERATING ACTIVITIES	$ 291,788	$ 408,418
Property, plant and equipment:
Capital expenditures	(102,820)	(241,142)
Change in accounts payable and accrued liabilities	(9,698)	319
Proceeds from sale of property, plant and equipment	2,750	892
Distributions received from investments in excess of cumulative earnings	841	2,309
Payments for acquisitions of businesses, net of cash acquired		(320,232)
Cash received from redemption of equity securities		134,288
Net cash used in investing activities	(108,927)	(423,566)
CASH FLOWS FROM FINANCING ACTIVITIES:
Borrowings under securitization facility	46,100	153,500
Payments under securitization facility	(47,700)	(179,000)
Proceeds from equipment financings	14,705	10,000
Payments on equipment financings	(10,622)	(1,021)
Borrowings under revolving credit facilities	70,000	300,000
Payments under revolving credit facilities	(190,000)	(235,000)
Payments on finance lease obligations	(8,204)	(23,270)
Payment of debt issuance costs	(5,821)
Payments for purchases of units under unit repurchase program		(5,251)
Payments for taxes related to net settlement of issuance of units in deferred compensation plans	(1,310)	(7,817)
Distributions paid to Partners	(51,753)	(208,653)	$ (278,425)
Other	(603)	(673)
Net cash used in financing activities	(185,208)	(197,185)
NET CHANGE IN CASH AND CASH EQUIVALENTS	(2,347)	(212,333)
CASH AND CASH EQUIVALENTS AT BEGINNING OF PERIOD	36,482	244,150	244,150
CASH AND CASH EQUIVALENTS AT END OF PERIOD	34,135	31,817	$ 36,482
SUPPLEMENTAL CASH FLOW INFORMATION:
Cash paid for interest	26,686	23,931
Cash paid for income taxes	10
SUPPLEMENTAL NON-CASH ACTIVITY:
Accounts payable for purchase of property, plant and equipment	4,806	14,904
Right-of-use assets acquired by operating lease	278	25,321
Market value of common units issued under deferred compensation plans before tax withholding requirements	$ 3,837	17,415
Fair value of liabilities assumed in acquisition of business		$ 1,921

ORGANIZATION AND PRESENTATION

ORGANIZATION AND PRESENTATION	9 Months Ended
	Sep. 30, 2020
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 "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 the coal mining operations of Alliance Resource Operating Partners, L.P. ● References to "Alliance Minerals" mean Alliance Minerals, LLC, the holding company for the oil and gas minerals interests of Alliance Resource Partners, L.P. ​ 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, 2020 and December 31, 2019, the results of our operations and comprehensive income for the three and nine months ended September 30, 2020 and 2019, and cash flows for the nine months ended September 30, 2020 and 2019. 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 of 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, 2019. ​ 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, 2020. ​ 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.

NEW ACCOUNTING STANDARDS

NEW ACCOUNTING STANDARDS	9 Months Ended
	Sep. 30, 2020
NEW ACCOUNTING STANDARDS
NEW ACCOUNTING STANDARDS	2. NEW ACCOUNTING STANDARDS ​ New Accounting Standards Issued and Adopted ​ In August 2018, the FASB issued ASU 2018-13, Fair Value Measurement (Topic 820): Disclosure Framework – Changes to the Disclosure Requirement for Fair Value Measurement. ASU 2018-13 amended the fair value measurement guidance by removing and modifying certain disclosure requirements, while also adding new disclosure requirements including the requirement to disclose the range and weighted average of significant unobservable inputs used to develop certain Level 3 measurements. These changes are to be applied prospectively for only the most recent interim or annual period presented in the year of adoption. We adopted ASU 2018-13 on January 1, 2020. ​ In June 2016, the FASB issued ASU 2016-13, Financial Instruments–Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments

ACQUISITION

ACQUISITION	9 Months Ended
	Sep. 30, 2020
ACQUISITION
ACQUISITION	3. ACQUISITION ​ Wing ​ On August 2, 2019 (the "Wing Acquisition Date"), our subsidiary, AR Midland, LP ("AR Midland") acquired from Wing Resources LLC and Wing Resources II LLC (collectively, "Wing") approximately 9,000 net royalty acres in the Midland Basin, with exposure to more than 400,000 gross acres, for a cash purchase price of $144.9 million (the "Wing Acquisition"). The purchase price was funded with cash on hand and borrowings under the Revolving Credit Facility discussed in Note 9 – Long-Term Debt. The Wing Acquisition enhances our ownership position in the Permian Basin, expands our exposure to industry leading operators and furthers our business strategy to grow our Minerals segment. Concurrent with the Wing Acquisition, JC Resources LP, an entity owned by Joseph W. Craft III, the Chairman, President and Chief Executive Officer of MGP ("Mr. Craft"), acquired from Wing, in a separate transaction, mineral interests that we elected not to acquire. ​ Because the mineral interests acquired in the Wing Acquisition include royalty interests in both producing properties and unproved properties, we have determined that the acquisition should be accounted for as a business combination and the underlying assets should be recorded at fair value as of the Wing Acquisition Date on our condensed consolidated balance sheet. During the nine months ended September 30, 2020, we recorded adjustments to our mineral interests in proved and unproved properties after receiving additional information regarding proved and unproved reserve quantities, production and projections as of the Wing Acquisition Date. In addition, we increased our receivables by $0.3 million as a result of information received from operators concerning royalty payments owed to us from production that occurred prior to the Wing Acquisition Date. ​ The following table summarizes our final fair value allocation of assets acquired as of the Wing Acquisition Date incorporating measurement period adjustments made to the allocation: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ As Previously ​ ​ ​ ​ ​ ​ ​ ​ Reported ​ Adjustments ​ Final ​ ​ ​ ​ ​ (in thousands) ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Mineral interests in proved properties ​ $ 58,084 ​ ​ 16,987 ​ $ 75,071 ​ Mineral interests in unproved properties ​ ​ 84,976 ​ ​ (17,275) ​ ​ 67,701 ​ Receivables ​ ​ 1,867 ​ ​ 288 ​ ​ 2,155 ​ Net assets acquired ​ $ 144,927 ​ ​ ​ ​ $ 144,927 ​ ​ The fair value of the mineral interests was determined using a weighting of both income and market approaches. Our income approach primarily comprised a discounted cash flow model. The assumptions used in the discounted cash flow model included estimated production, projected cash flows, forward oil & gas prices and a weighted average cost of capital. Our market approach consisted of the observation of recent acquisitions in the Permian Basin to determine a market price for similar mineral interests. Certain assumptions used in our valuation are not observable in active markets; therefore, the fair value measurements represent Level 3 fair value measurements. The carrying value of the receivables represents the fair value given the short-term nature of the receivables.

LONG-LIVED ASSET IMPAIRMENTS

LONG-LIVED ASSET IMPAIRMENTS	9 Months Ended
	Sep. 30, 2020
LONG-LIVED ASSET IMPAIRMENTS
LONG-LIVED ASSET IMPAIRMENTS	4. LONG-LIVED ASSET IMPAIRMENTS ​ During the nine months ended September 30, 2020, we recorded $25.0 million of non-cash asset impairment charges in our Illinois Basin 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 nine months ended September 30, 2019, we recorded an asset impairment charge of $15.2 million in our Illinois Basin segment due to the cessation of coal production at our Dotiki mine, effective August 16, 2019, in an effort to focus on maximizing production at our lower-cost mines in the segment. We adjusted the carrying value of Dotiki's assets from $35.9 million to its fair value of $25.8 million and accrued $5.1 million with respect to scheduled payments to WKY CoalPlay, LLC ("WKY CoalPlay") for leased coal reserves from which we may not receive future economic benefit. See Note 10 – Variable Interest Entities for more information about WKY CoalPlay. ​ The fair values of the impaired assets were determined using a market approach, which represent Level 3 fair value measurements under the fair value hierarchy. The fair value analysis used assumptions regarding the marketability of certain assets in the Illinois Basin. ​ With the uncertainty related to energy demand as a result of a) weak electricity demand and b) an oversupply and lack of storage for oil and natural gas during the quarter ended March 31, 2020 (the "First Quarter"), both due in part to the COVID-19 pandemic and other market and production factors impacting both our coal mining operations and our mineral interests activities, we performed recoverability tests during the First Quarter using undiscounted cash flows based on our estimate of both volume and prices from information available to us and determined we would be able to recover the costs of our assets, excluding the impaired assets discussed above. Amid cost reduction efforts, increased customer commitments for coal, a modest recovery in commodity futures prices and increased clarity into production levels by operators of our oil & gas mineral interests, we determined impairment of our long-lived assets subsequent to the First Quarter was not necessary. The cash flow estimates used in our impairment assessments, by their very nature, are dependent on conditions that could materially change in future periods based on new information. If in future periods changes to these estimates were to materially reduce our expected cash flows, additional impairments could be necessary.

GOODWILL IMPAIRMENT

GOODWILL IMPAIRMENT	9 Months Ended
	Sep. 30, 2020
GOODWILL IMPAIRMENT
GOODWILL IMPAIRMENT	5. GOODWILL IMPAIRMENT ​ At December 31, 2019, our consolidated balance sheet included $136.4 million of goodwill, of which $132.0 million was associated with the reporting unit representing our Hamilton County Coal, LLC ("Hamilton") mine, which is included in our Illinois Basin segment. The goodwill associated with our Hamilton mine was recorded in conjunction with our acquisition of the Hamilton mine on July 31, 2015. During the First Quarter, 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 Hamilton and c) our actual performance during the First Quarter. After consideration of these events and changes in circumstances, we performed an interim test of the goodwill associated with the Hamilton reporting unit comparing Hamilton's carrying amount to its fair value. ​ We estimated the fair value of the Hamilton reporting unit 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 are not observable in active markets; therefore, the fair value measurements represent Level 3 fair value measurements. The fair value of the Hamilton reporting unit was determined to be below its carrying amount (including goodwill) by more than the recorded balance of goodwill associated with the reporting unit. Accordingly, we recognized an impairment charge of $132.0 million consisting of the total carrying amount of goodwill allocated to the Hamilton reporting unit. This impairment charge reduced our consolidated goodwill balance to $4.4 million. During the First Quarter, 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, 2020
CONTINGENCIES
CONTINGENCIES	6. CONTINGENCIES ​ Various lawsuits, claims and regulatory proceedings incidental to our business 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, 2020
INVENTORIES
INVENTORIES	7. INVENTORIES ​ Inventories consist of the following: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ September 30, ​ December 31, ​ ​ ​ 2020 2019 ​ ​ (in thousands) ​ ​ ​ ​ ​ ​ ​ ​ ​ Coal ​ $ 38,531 ​ $ 63,645 ​ Supplies (net of reserve for obsolescence of $5,577 and $5,555, respectively) ​ 36,348 ​ 37,660 ​ Total inventories, net ​ $ 74,879 ​ $ 101,305 ​ ​

FAIR VALUE MEASUREMENTS

FAIR VALUE MEASUREMENTS	9 Months Ended
	Sep. 30, 2020
FAIR VALUE MEASUREMENTS
FAIR VALUE MEASUREMENTS	8. FAIR VALUE MEASUREMENTS ​ The following table summarizes our fair value measurements within the hierarchy not included elsewhere in these notes: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ September 30, 2020 ​ December 31, 2019 ​ ​ Level 1 Level 2 Level 3 Level 1 Level 2 Level 3 ​ ​ (in thousands) ​ Long-term debt ​ $ — ​ $ 494,712 ​ $ — ​ $ — ​ $ 736,206 ​ $ — ​ Total ​ $ — ​ $ 494,712 ​ $ — ​ $ — ​ $ 736,206 ​ $ — ​ ​ 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 9 – 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, 2020
LONG-TERM DEBT
LONG-TERM DEBT	9. 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, ​ ​ 2020 2019 2020 2019 ​ ​ (in thousands) ​ Revolving credit facility ​ $ 135,000 ​ $ 255,000 ​ $ (7,280) ​ $ (3,050) ​ Senior notes ​ 400,000 ​ 400,000 ​ (4,192) ​ (4,879) ​ Securitization facility ​ ​ 72,200 ​ ​ 73,800 ​ ​ — ​ ​ — ​ May 2019 equipment financing ​ ​ 5,785 ​ ​ 8,199 ​ ​ — ​ ​ — ​ November 2019 equipment financing ​ ​ 44,890 ​ ​ 52,281 ​ ​ — ​ ​ — ​ June 2020 equipment financing ​ ​ 13,887 ​ ​ — ​ ​ — ​ ​ — ​ ​ ​ 671,762 ​ 789,280 ​ (11,472) ​ (7,929) ​ Less current maturities ​ (89,271) ​ (13,157) ​ — ​ — ​ Total long-term debt ​ $ 582,491 ​ $ 776,123 ​ $ (11,472) ​ $ (7,929) ​ ​ 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 of the assets of the Restricted Subsidiaries. The Credit Agreement is not guaranteed or secured by the assets of the Intermediate Partnership's oil & gas minerals subsidiary, Alliance Minerals, or its direct and indirect subsidiaries (collectively the "Unrestricted Subsidiaries"). 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 3.01% as of September 30, 2020. At September 30, 2020, we had $21.8 million of letters of credit outstanding with $381.0 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 1.69 to 1.0, 8.22 to 1.0 and 0.69 to 1.0, respectively, for the trailing twelve months ended September 30, 2020. We remain in compliance with the covenants of the Credit Agreement as of September 30, 2020. ​ Senior Notes. 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 back 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% that provides 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. At maturity, the equipment will revert back 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 back to the Intermediate Partnership.

VARIABLE INTEREST ENTITIES

VARIABLE INTEREST ENTITIES	9 Months Ended
	Sep. 30, 2020
VARIABLE INTEREST ENTITIES
VARIABLE INTEREST ENTITIES	​ ​ 10. 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 ​ ​ 86,384 ​ ​ 3,598 ​ ​ 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 income. ​ 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. ​ WKY CoalPlay ​ On November 17, 2014, SGP Land, LLC ("SGP Land"), an entity owned indirectly by the Chairman, President and CEO of MGP ("Mr. Craft") and Kathleen S. Craft, jointly, and two limited liability companies ("Craft Companies") owned by irrevocable trusts established by Mr. Craft and his children, entered into a limited liability company agreement to form WKY CoalPlay. WKY CoalPlay was formed, in part, to purchase and lease coal reserves. WKY CoalPlay is managed by an individual who is an officer and director of Alliance Resource Holdings II, Inc. and trustee of the irrevocable trusts owning one of the Craft Companies. In December 2014 and February 2015, we entered into various coal reserve leases with WKY CoalPlay. During the nine months ended September 30, 2020, we paid $10.8 million to WKY CoalPlay under these leases. ​ As discussed in Item 8. Financial Statements and Supplementary Data—Note 20 – Related-Party Transactions in our Annual Report on Form 10-K for the year ended December 31, 2019, we have the option to acquire the coal reserves leased from WKY CoalPlay at any time during a three-year period ending in December 2020, with respect to a portion of the reserves, and ending in February 2021 with respect to the remainder of the reserves. In all cases, the options provide for a purchase price that would provide WKY CoalPlay a 7.0% internal rate of return on its investment in the reserves taking into account payments previously made under the leases. ​ We have concluded that WKY CoalPlay is a VIE because of our ability to exercise options to acquire reserves under lease with WKY CoalPlay, which is not within the control of the equity holders and, if it occurs, could potentially limit the expected residual return to the owners of WKY CoalPlay. Once the options expire in December 2020 and February 2021, WKY CoalPlay will cease to be a VIE. We do not have any economic or governance rights related to WKY CoalPlay and our options that provide us with a variable interest in WKY CoalPlay's reserve assets do not give us any rights that constitute power to direct the primary activities that most significantly impact WKY CoalPlay's economic performance. SGP Land has the sole ability to replace the manager of WKY CoalPlay at its discretion and therefore has power to direct the activities of WKY CoalPlay. Consequently, we concluded that SGP Land is the primary beneficiary of WKY CoalPlay.

INVESTMENTS

INVESTMENTS	9 Months Ended
	Sep. 30, 2020
INVESTMENTS
INVESTMENTS	11. INVESTMENTS ​ AllDale III ​ As discussed in Note 10 – 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, ​ ​ 2020 2019 2020 2019 ​ ​ ​ (in thousands) ​ Beginning balance ​ $ 27,705 ​ $ 28,672 ​ $ 28,529 ​ $ 28,974 ​ Equity method investment income ​ ​ 62 ​ ​ 659 ​ ​ 650 ​ ​ 1,533 ​ Distributions received ​ ​ (352) ​ ​ (610) ​ ​ (1,491) ​ ​ (1,786) ​ Other ​ ​ — ​ ​ — ​ ​ (273) ​ ​ — ​ Ending balance ​ $ 27,415 ​ $ 28,721 ​ $ 27,415 ​ $ 28,721 ​ ​ As discussed in Note 4 – Long-Lived Asset Impairments, there was uncertainty related to energy demand in the First Quarter as a result of a) weak electricity demand and b) an oversupply and lack of storage for oil and natural gas, both due in part to the COVID-19 pandemic and other market and production factors, which could have impacted our investment in AllDale III. As a result, as part of our First Quarter impairment assessment, we compared the fair value of our investment to its carrying value and concluded that the fair value exceeded the carrying value and no impairment in our investment was necessary. In our subsequent quarterly impairment assessments, amid a modest recovery in commodity futures prices and increased clarity into production levels by operators, we again compared the fair value of our investment to its carrying value and concluded no impairment was necessary. To calculate the fair value of the investment we used an income approach utilizing a discounted cash flow model based on our estimate of both volume, prices and expenses from information available to us. Key assumptions used in our valuation are not observable in active markets; therefore, the fair value measurements represent Level 3 fair value measurements. The cash flow estimates used in our assessments, by their very nature, are dependent on conditions that could materially change in future periods based on new information. If in future periods changes to these estimates were to materially reduce our expected cash flows, an impairment of our investment could be necessary. ​ Kodiak ​ On July 19, 2017, Alliance Minerals purchased $100 million of Series A-1 Preferred Interests from Kodiak Gas Services, LLC ("Kodiak"), a privately-held company providing large-scale, high-utilization gas compression assets to customers operating primarily in the Permian Basin. This structured investment provided us with a quarterly cash or payment-in-kind return. On February 8, 2019, Kodiak redeemed our preferred interest for $135.0 million in cash resulting in an $11.5 million gain due to an early redemption premium. The gain is included in the Equity securities income

PARTNERS' CAPITAL

PARTNERS' CAPITAL	9 Months Ended
	Sep. 30, 2020
PARTNERS' CAPITAL
PARTNERS' CAPITAL	12. PARTNERS' CAPITAL ​ Distributions ​ Distributions paid or declared during 2019 and 2020 were as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ Payment Date Per Unit Cash Distribution Total Cash Distribution ​ ​ ​ ​ ​ (in thousands) ​ ​ ​ ​ ​ ​ ​ ​ ​ February 14, 2019 ​ $ 0.5300 ​ $ 69,011 ​ May 15, 2019 ​ ​ 0.5350 ​ ​ 69,489 ​ August 14, 2019 ​ ​ 0.5400 ​ ​ 70,153 ​ November 14, 2019 ​ ​ 0.5400 ​ ​ 69,772 ​ Total ​ $ 2.1450 ​ $ 278,425 ​ ​ ​ ​ ​ ​ ​ ​ ​ February 14, 2020 ​ $ 0.4000 ​ $ 51,753 ​ Total ​ $ 0.4000 ​ $ 51,753 ​ ​ In response to the disruptions to the economy and the uncertainty surrounding the COVID-19 pandemic, the Board of Directors of ARLP's general partner began suspending cash distributions to unitholders with the First Quarter and has continued through the quarter ended December 31, 2020. ​ 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, 2020. 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. Total units repurchased include the repurchase and retirement of 35 units representing fractional units as part of the simplification transactions completed by the ARLP Partnership on May 31, 2018 which are not part of the unit repurchase program. ​ Change in Partners' Capital ​ The following tables present the quarterly change in Partners' Capital for the nine months ended September 30, 2020 and 2019: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 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 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Accumulated ​ ​ ​ ​ ​ ​ ​ ​ ​ Number of ​ Limited ​ Other ​ ​ ​ ​ ​ ​ ​ ​ ​ Limited Partner ​ Partners' ​ Comprehensive ​ Noncontrolling ​ Total Partners' ​ ​ Units Capital Loss Interest Capital ​ ​ (in thousands, except unit data) ​ Balance at January 1, 2019 128,095,511 ​ $ 1,229,268 ​ $ (46,871) ​ $ 5,290 ​ $ 1,187,687 ​ Comprehensive income: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Net income — ​ 276,428 ​ — ​ ​ 7,176 283,604 ​ Actuarially determined long-term liability adjustments — ​ — ​ (3,584) ​ — (3,584) ​ Total comprehensive income ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 280,020 ​ Settlement of deferred compensation plans 596,650 ​ (7,817) ​ ​ — ​ ​ — ​ ​ (7,817) ​ Purchase of units under unit repurchase program (300,970) ​ (5,251) ​ ​ — ​ ​ — ​ ​ (5,251) ​ Common unit-based compensation — ​ 2,743 ​ ​ — ​ ​ — ​ ​ 2,743 ​ Distributions on deferred common unit-based compensation — ​ (1,280) ​ ​ — ​ ​ — ​ ​ (1,280) ​ Distributions from consolidated company to noncontrolling interest ​ — ​ ​ — ​ ​ — ​ ​ (262) ​ ​ (262) ​ Distributions to Partners — ​ ​ (67,731) ​ ​ — ​ ​ — ​ ​ (67,731) ​ Balance at March 31, 2019 128,391,191 ​ ​ 1,426,360 ​ ​ (50,455) ​ ​ 12,204 ​ ​ 1,388,109 ​ Comprehensive income: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Net income — ​ 58,070 ​ — ​ ​ 114 58,184 ​ Actuarially determined long-term liability adjustments — ​ — ​ (118) ​ — (118) ​ Total comprehensive income ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 58,066 ​ Common unit-based compensation — ​ 3,021 ​ ​ — ​ ​ — ​ ​ 3,021 ​ Distributions on deferred common unit-based compensation — ​ (799) ​ ​ — ​ ​ — ​ ​ (799) ​ Distributions from consolidated company to noncontrolling interest ​ — ​ ​ — ​ ​ — ​ ​ (228) ​ ​ (228) ​ Distributions to Partners — ​ ​ (68,690) ​ ​ — ​ ​ — ​ ​ (68,690) ​ Balance at June 30, 2019 128,391,191 ​ ​ 1,417,962 ​ ​ (50,573) ​ ​ 12,090 ​ ​ 1,379,479 ​ Comprehensive income: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Net income — ​ 39,084 ​ — ​ ​ 117 39,201 ​ Actuarially determined long-term liability adjustments — ​ — ​ (119) ​ — (119) ​ Total comprehensive income ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 39,082 ​ Common unit-based compensation — ​ 3,066 ​ ​ — ​ ​ — ​ ​ 3,066 ​ Distributions on deferred common unit-based compensation — ​ (822) ​ ​ — ​ ​ — ​ ​ (822) ​ Distributions from consolidated company to noncontrolling interest ​ — ​ ​ — ​ ​ — ​ ​ (183) ​ ​ (183) ​ Distributions to Partners — ​ ​ (69,331) ​ ​ — ​ ​ — ​ ​ (69,331) ​ Balance at September 30, 2019 128,391,191 ​ $ 1,389,959 ​ $ (50,692) ​ $ 12,024 ​ $ 1,351,291 ​ ​

REVENUE FROM CONTRACTS WITH CUS

REVENUE FROM CONTRACTS WITH CUSTOMERS	9 Months Ended
	Sep. 30, 2020
REVENUE FROM CONTRACTS WITH CUSTOMERS
REVENUE FROM CONTRACTS WITH CUSTOMERS	13. 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 18 – Segment Information. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Illinois ​ ​ Other and ​ ​ ​ ​ ​ Basin Appalachia Minerals Corporate Elimination Consolidated ​ ​ ​ (in thousands) ​ Three Months Ended September 30, 2020 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Coal sales ​ $ 206,356 ​ $ 129,411 ​ $ — ​ $ — ​ $ — ​ $ 335,767 ​ Oil & gas royalties ​ ​ — ​ ​ — ​ ​ 9,693 ​ ​ — ​ ​ — ​ ​ 9,693 ​ Transportation revenues ​ ​ 3,722 ​ ​ 2,504 ​ ​ — ​ ​ — ​ ​ — ​ ​ 6,226 ​ Other revenues ​ ​ 282 ​ ​ 395 ​ ​ 28 ​ ​ 6,070 ​ ​ (2,810) ​ ​ 3,965 ​ Total revenues ​ $ 210,360 ​ $ 132,310 ​ $ 9,721 ​ $ 6,070 ​ $ (2,810) ​ $ 355,651 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Three Months Ended September 30, 2019 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Coal sales ​ $ 256,293 ​ $ 162,316 ​ $ — ​ $ 5,689 ​ $ (4,293) ​ $ 420,005 ​ Oil & gas royalties ​ ​ — ​ ​ — ​ ​ 13,969 ​ ​ — ​ ​ — ​ ​ 13,969 ​ Transportation revenues ​ ​ 18,778 ​ ​ 1,246 ​ ​ — ​ ​ — ​ ​ — ​ ​ 20,024 ​ Other revenues ​ ​ 5,264 ​ ​ 852 ​ ​ 208 ​ ​ 7,434 ​ ​ (3,030) ​ ​ 10,728 ​ Total revenues ​ $ 280,335 ​ $ 164,414 ​ $ 14,177 ​ $ 13,123 ​ $ (7,323) ​ $ 464,726 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Nine Months Ended September 30, 2020 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Coal sales ​ $ 539,614 ​ $ 347,076 ​ $ — ​ $ — ​ $ — ​ $ 886,690 ​ Oil & gas royalties ​ ​ — ​ ​ — ​ ​ 31,718 ​ ​ — ​ ​ — ​ ​ 31,718 ​ Transportation revenues ​ ​ 10,731 ​ ​ 5,991 ​ ​ — ​ ​ — ​ ​ — ​ ​ 16,722 ​ Other revenues ​ ​ 1,674 ​ ​ 14,456 ​ ​ 113 ​ ​ 18,409 ​ ​ (8,166) ​ ​ 26,486 ​ Total revenues ​ $ 552,019 ​ $ 367,523 ​ $ 31,831 ​ $ 18,409 ​ $ (8,166) ​ $ 961,616 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Nine Months Ended September 30, 2019 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Coal sales ​ $ 875,544 ​ $ 477,720 ​ $ — ​ $ 16,530 ​ $ (12,463) ​ $ 1,357,331 ​ Oil & gas royalties ​ ​ — ​ ​ — ​ ​ 36,254 ​ ​ — ​ ​ — ​ ​ 36,254 ​ Transportation revenues ​ ​ 79,303 ​ ​ 3,589 ​ ​ — ​ ​ — ​ ​ — ​ ​ 82,892 ​ Other revenues ​ ​ 10,557 ​ ​ 2,753 ​ ​ 1,079 ​ ​ 26,745 ​ ​ (9,229) ​ ​ 31,905 ​ Total revenues ​ $ 965,404 ​ $ 484,062 ​ $ 37,333 ​ $ 43,275 ​ $ (21,692) ​ $ 1,508,382 ​ ​ 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, 2020 and disaggregated by segment and contract duration. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 2023 and ​ ​ ​ ​ 2020 2021 2022 Thereafter Total ​ ​ (in thousands) ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Illinois Basin coal revenues ​ $ 248,362 ​ $ 618,966 ​ $ 238,514 ​ $ 307,695 ​ $ 1,413,537 ​ Appalachia coal revenues ​ ​ 138,340 ​ ​ 130,075 ​ ​ 57,891 ​ ​ — ​ ​ 326,306 ​ Total coal revenues (1) ​ $ 386,702 ​ $ 749,041 ​ $ 296,405 ​ $ 307,695 ​ $ 1,739,843 ​ (1) Coal revenues generally consists of consolidated revenues excluding our Minerals segment .

EARNINGS PER LIMITED PARTNER UN

EARNINGS PER LIMITED PARTNER UNIT	9 Months Ended
	Sep. 30, 2020
EARNINGS PER LIMITED PARTNER UNIT
EARNINGS PER LIMITED PARTNER UNIT	14. 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 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, 2020 and 2019: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Three Months Ended ​ Nine Months Ended ​ ​ ​ September 30, ​ September 30, ​ ​ 2020 2019 2020 2019 ​ ​ (in thousands, except per unit data) ​ Net income (loss) attributable to ARLP ​ $ 27,199 ​ $ 39,084 ​ $ (164,248) ​ $ 373,582 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Less: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Distributions to participating securities ​ — ​ (1,133) ​ — ​ (3,360) ​ Undistributed earnings attributable to participating securities ​ (581) ​ — ​ — ​ (2,655) ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Net income (loss) attributable to ARLP available to limited partners ​ $ 26,618 ​ $ 37,951 ​ $ (164,248) ​ $ 367,567 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted-average limited partner units outstanding – basic and diluted ​ 127,195 ​ 128,391 ​ 127,154 ​ 128,312 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Earnings per limited partner unit - basic and diluted (1) ​ $ 0.21 ​ $ 0.30 ​ $ (1.29) ​ $ 2.86 ​ (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 661 and 656 for the three and nine months ended September 30, 2020, respectively, and 1,133 and 1,216 for the three and nine months ended September 30, 2019, respectively, were considered anti-dilutive under the treasury stock method .

WORKERS' COMPENSATION AND PNEUM

WORKERS' COMPENSATION AND PNEUMOCONIOSIS	9 Months Ended
	Sep. 30, 2020
ACCRUED WORKERS' COMPENSATION AND PNEUMOCONIOSIS BENEFITS
WORKERS' COMPENSATION AND PNEUMOCONIOSIS	15. 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, ​ ​ ​ 2020 2019 2020 2019 ​ ​ ​ (in thousands) ​ Beginning balance ​ $ 54,478 ​ $ 53,425 ​ $ 53,384 ​ $ 49,539 ​ Accruals increase ​ 1,599 ​ 2,395 ​ 3,539 ​ 6,603 ​ Payments ​ (2,123) ​ (2,663) ​ (6,686) ​ (8,588) ​ Interest accretion ​ 319 ​ 402 ​ 958 ​ 1,204 ​ Valuation loss (1) ​ — ​ — ​ 3,078 ​ 4,801 ​ Ending balance ​ $ 54,273 ​ $ 53,559 ​ $ 54,273 ​ $ 53,559 ​ (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. We conducted a 2020 mid-year review of our actuarial assumptions which resulted in a valuation loss due to unfavorable changes in claims development and a decrease in the discount rate from 2.81% to 2.05% . Our 2019 mid-year actuarial review resulted in a valuation loss due to unfavorable changes in claims development and a decrease in the discount rate from 3.89% to 3.06% . ​ 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, 2020 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, ​ ​ ​ 2020 2019 2020 2019 ​ ​ (in thousands) ​ Service cost ​ $ 882 ​ $ 656 ​ $ 2,643 ​ $ 1,947 Interest cost (1) ​ 750 ​ 761 ​ 2,249 ​ 2,283 ​ Net amortization (1) ​ (172) ​ (1,145) ​ (515) ​ (3,436) ​ Net periodic benefit cost ​ $ 1,460 ​ $ 272 ​ $ 4,377 ​ $ 794 ​ (1) Interest cost and net amortization are included in the Other expense line item within our condensed consolidated statements of income.

COMPENSATION PLANS

COMPENSATION PLANS	9 Months Ended
	Sep. 30, 2020
COMPENSATION PLANS
COMPENSATION PLANS	16. 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. The LTIP awards are grants of non-vested "phantom" or notional units, also referred to as "restricted units", which upon satisfaction of time and performance-based vesting requirements, entitle the LTIP participant to receive ARLP common units. Annual grant levels and vesting provisions for designated participants are recommended by the Chairman, President and Chief Executive Officer of MGP, subject to review and approval of the compensation committee of the MGP board of directors (the "Compensation Committee"). Vesting of all grants outstanding is subject to the satisfaction of certain financial tests. If it is not probable the financial tests for a particular grant will be met, any previously expensed amounts for the grant are reversed and no future expense will be recognized for those grants. Assuming the financial tests are met, grants issued to LTIP participants are expected to cliff vest on January 1st of the third year following issuance of the grants. We expect to settle these grants by delivery of 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 grants as they occur. As provided under the distribution equivalent rights ("DERs") provisions of the LTIP and the terms of the LTIP awards, all non-vested grants 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. ​ A summary of non-vested LTIP grants as of and for the nine months ended September 30, 2020 is as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ Number of units Weighted average grant date fair value per unit ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Non-vested grants at January 1, 2020 ​ 1,603,378 ​ ​ ​ ​ Granted 950,035 ​ $ 9.62 ​ Vested (1) (424,486) ​ 23.22 ​ Forfeited (13,835) ​ 16.13 ​ Non-vested grants at September 30, 2020 (2) 2,115,092 ​ ​ ​ (1) During the nine months ended September 30, 2020, we issued 279,622 unrestricted common units to the LTIP participants. The remaining vested units were settled in cash to satisfy tax withholding obligations of the LTIP participants. (2) Represents total non-vested grants outstanding including 675,302 restricted units that were granted in 2019 (the "2019 Grants"). During the First Quarter, it was determined that the vesting requirements for the 2019 Grants were not probable of being satisfied. ​ LTIP expense was $1.6 million and $2.7 million for the three months ended September 30, 2020 and 2019, respectively, and $2.5 million and $7.9 million for the nine months ended September 30, 2020 and 2019, respectively. LTIP expense for the nine months ended September 30, 2020 includes the reversal in the First Quarter 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 the LTIP as of September 30, 2020 was $11.3 million and is included in the partners' capital Limited partners-common unitholders ​ As of September 30, 2020, we had 1,439,790 restricted units that are expected to vest, with a weighted average grant date fair value of $13.33 per unit and an intrinsic value of $4.0 million at $2.77 per unit. There was $7.9 million in total unrecognized compensation expense related to the non-vested LTIP grants that are expected to vest. That expense is expected to be recognized over a weighted-average period of 1.6 years. ​ After consideration of the January 1, 2020 vesting and subsequent issuance of 279,622 common units, approximately 1.0 million units remain available under the LTIP for issuance in the future. This available issuance excludes all grants currently outstanding. Adding back the 2019 Grants that are not probable to vest, approximately 1.7 million units remain available under the LTIP for issuance in the future. ​ 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, 2020 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, 2020 ​ 631,365 ​ $ 25.48 ​ $ 6,831 ​ Granted ​ 29,544 ​ ​ 7.87 ​ ​ ​ ​ Phantom units outstanding as of September 30, 2020 660,909 ​ 24.69 ​ ​ 1,831 ​ ​ Total SERP and Directors' Deferred Compensation Plan expense was $0.1 million and $0.4 million for the three months ended September 30, 2020 and 2019, respectively, and $0.4 million and $1.1 million for the nine months ended September 30, 2020 and 2019, respectively. As of September 30, 2020, the total obligation associated with the SERP and Directors' Deferred Compensation Plan was $16.3 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, 2020
COMPONENTS OF PENSION PLAN NET PERIODIC BENEFIT COSTS
COMPONENTS OF PENSION PLAN NET PERIODIC BENEFIT COSTS	17. 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, ​ ​ ​ 2020 2019 2020 2019 ​ ​ (in thousands) ​ Interest cost ​ $ 1,030 ​ $ 1,217 ​ $ 3,138 ​ $ 3,649 ​ Expected return on plan assets ​ (1,413) ​ (1,233) ​ (4,396) ​ (3,699) ​ Amortization of prior service cost ​ ​ 47 ​ ​ 46 ​ ​ 140 ​ ​ 139 ​ Amortization of net loss ​ 969 ​ 980 ​ 3,096 ​ 2,941 ​ Net periodic benefit cost (1) ​ $ 633 ​ $ 1,010 ​ $ 1,978 ​ $ 3,030 ​ (1) Net periodic benefit cost for the Pension Plan is included in the Other expense line item within our condensed consolidated statements of income. ​ During the nine months ended September 30, 2020, we made contribution payments of $1.7 million to the Pension Plan for the 2019 plan year. We expect to defer additional contributions to the Pension Plan until December 2020 as permitted under the Coronavirus Aid Relief and Economic Security Act of 2020 enacted in response to the COVID-19 pandemic.

SEGMENT INFORMATION

SEGMENT INFORMATION	9 Months Ended
	Sep. 30, 2020
SEGMENT INFORMATION
SEGMENT INFORMATION	18. SEGMENT INFORMATION ​ We operate in the United States as a diversified natural resource company that generates income from the production and marketing of coal to major domestic and international utilities and industrial users as well as income from oil & gas mineral interests. We aggregate multiple operating segments into three reportable segments, Illinois Basin, Appalachia, and Minerals. We also have an "all other" category referred to as Other and Corporate. Our two coal 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 segments include seven mining complexes operating in Illinois, Indiana, Kentucky, Maryland and West Virginia and a coal loading terminal in Indiana on the Ohio River. The Minerals reportable segment aggregates our oil & gas mineral interests which are located primarily in the Permian (Delaware and Midland), Anadarko (SCOOP/STACK), and Williston (Bakken) basins. We have no operations within our Minerals reportable segment other than receiving royalties and lease bonuses for our oil & gas mineral interests. ​ The Illinois Basin reportable segment includes currently operating mining complexes (a) Gibson County Coal, LLC's ("Gibson") mining complex, which includes the Gibson South mine, (b) Warrior Coal, LLC's ("Warrior") mining complex, (c) River View Coal, LLC's ("River View") mining complex and (d) Hamilton's mining complex. The Illinois Basin reportable segment also includes our currently operating Mt. Vernon Transfer Terminal, LLC ("Mt. Vernon") coal loading terminal in Indiana on the Ohio River. ​ The Illinois Basin reportable segment also includes Mid-America Carbonates, LLC ("MAC") and other support services as well as non-operating mining complexes (a) Gibson North mine, which ceased production in the fourth quarter of 2019, (b) Webster County Coal, LLC's Dotiki mining complex, which ceased production in August 2019, (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 reportable segment includes currently operating mining complexes (a) Mettiki mining complex, (b) Tunnel Ridge, LLC mining complex and (c) MC Mining, LLC ("MC Mining") mining complex. The Mettiki mining complex includes Mettiki Coal (WV), LLC's Mountain View mine and Mettiki Coal, LLC's preparation plant. The Appalachia reportable segment also includes the Penn Ridge assets, which are primarily coal mineral interests. ​ The Minerals reportable segment includes oil & gas mineral interests held by AR Midland and AllDale I & II and includes Alliance Minerals' equity interests in both AllDale III (Note 11 – Investments) and Cavalier Minerals. AR Midland acquired its mineral interest in the Wing Acquisition (Note 3 – Acquisition). ​ Other and Corporate 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"), Alliance Coal's coal brokerage activity and Alliance Minerals' prior equity investment in Kodiak. In February 2019, Kodiak redeemed our equity investment (see Note 11 – Investments). In addition, Other and Corporate includes certain Alliance Resource Properties, LLC's land and coal mineral interest activities, Pontiki Coal, LLC's workers' compensation and pneumoconiosis liabilities, Wildcat Insurance, LLC ("Wildcat Insurance"), which assists the ARLP Partnership with its insurance requirements, and AROP Funding and Alliance Finance (both discussed in Note 9 – Long-Term Debt). ​ In response to the impacts of the COVID-19 pandemic, we announced on March 30, 2020 a temporary cessation of coal production at our River View, Gibson, Hamilton and Warrior mining complexes in our Illinois Basin segment and on April 9, 2020 a temporary cessation of coal production at our MC Mining complex in our Appalachia segment. Underground production operations resumed in the second quarter at each of our mining complexes. All of our seven mining complexes are now producing coal. However, several mines continue running at less than capacity due to a limited spot market in the U.S. and a seaborne market that continues to be sub-economic for U.S. production. Due to the ongoing and unforeseen impacts of the COVID-19 pandemic, on April 15, 2020, 116 employees of the Gibson County mining complex and 78 employees of the Hamilton mining complex were notified that their employment would be terminated permanently on April 26, 2020. In addition to reduced production levels and employment adjustments, we have also taken numerous actions to optimize cash flows and preserve liquidity by reducing capital expenditures, working capital, costs and expenses, including adjusting our corporate support structure to better align to current operating levels. ​ Reportable segment results are presented below. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Illinois ​ ​ Other and Elimination ​ ​ ​ Basin Appalachia Minerals Corporate (1) Consolidated ​ ​ (in thousands) Three Months Ended September 30, 2020 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Revenues - Outside ​ $ 210,360 ​ $ 132,310 ​ $ 9,721 ​ $ 3,260 ​ $ — ​ $ 355,651 ​ Revenues - Intercompany ​ ​ — ​ ​ — ​ ​ — ​ ​ 2,810 ​ ​ (2,810) ​ ​ — ​ Total revenues (2) ​ ​ 210,360 ​ ​ 132,310 ​ ​ 9,721 ​ ​ 6,070 ​ ​ (2,810) ​ ​ 355,651 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Segment Adjusted EBITDA Expense (3) ​ 125,021 ​ 86,447 ​ 849 ​ 4,908 ​ (475) ​ 216,750 ​ Segment Adjusted EBITDA (4) ​ 81,617 ​ 43,358 ​ 8,898 ​ 1,163 ​ (2,335) ​ 132,701 ​ Capital expenditures ​ 3,815 ​ 14,541 ​ — ​ 219 ​ — ​ 18,575 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Three Months Ended September 30, 2019 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Revenues - Outside ​ $ 276,042 ​ $ 164,414 ​ $ 14,177 ​ $ 10,093 ​ $ — ​ $ 464,726 ​ Revenues - Intercompany ​ ​ 4,293 ​ ​ — ​ ​ — ​ ​ 3,030 ​ ​ (7,323) ​ ​ — ​ Total revenues (2) ​ ​ 280,335 ​ ​ 164,414 ​ ​ 14,177 ​ ​ 13,123 ​ ​ (7,323) ​ ​ 464,726 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Segment Adjusted EBITDA Expense (3) ​ 173,779 ​ 107,990 ​ 2,517 ​ 9,878 ​ (5,083) ​ 289,081 ​ Segment Adjusted EBITDA (4) ​ 87,780 ​ 55,178 ​ 12,202 ​ 3,243 ​ (2,240) ​ 156,163 ​ Capital expenditures ​ 49,829 ​ 25,056 ​ — ​ 630 ​ — ​ 75,515 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Nine Months Ended September 30, 2020 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Revenues - Outside ​ $ 552,019 ​ $ 367,523 ​ $ 31,831 ​ $ 10,243 ​ $ — ​ $ 961,616 ​ Revenues - Intercompany ​ ​ — ​ ​ — ​ ​ — ​ ​ 8,166 ​ ​ (8,166) ​ ​ — ​ Total revenues (2) ​ ​ 552,019 ​ ​ 367,523 ​ ​ 31,831 ​ ​ 18,409 ​ ​ (8,166) ​ ​ 961,616 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Segment Adjusted EBITDA Expense (3) ​ 383,486 ​ ​ 240,116 ​ ​ 2,851 ​ ​ 13,697 ​ ​ (1,161) ​ 638,989 ​ Segment Adjusted EBITDA (4) ​ 157,803 ​ ​ 121,416 ​ ​ 29,534 ​ ​ 4,710 ​ ​ (7,005) ​ 306,458 ​ Total assets ​ 1,082,992 ​ ​ 470,261 ​ ​ 616,491 ​ ​ 468,590 ​ ​ (406,994) ​ 2,231,340 ​ Capital expenditures ​ 44,073 ​ ​ 57,798 ​ ​ — ​ ​ 949 ​ ​ — ​ 102,820 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Nine Months Ended September 30, 2019 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Revenues - Outside ​ $ 952,941 ​ $ 484,062 ​ $ 37,333 ​ $ 34,046 ​ $ — ​ $ 1,508,382 ​ Revenues - Intercompany ​ ​ 12,463 ​ ​ — ​ ​ — ​ ​ 9,229 ​ ​ (21,692) ​ ​ — ​ Total revenues (2) ​ ​ 965,404 ​ ​ 484,062 ​ ​ 37,333 ​ ​ 43,275 ​ ​ (21,692) ​ ​ 1,508,382 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Segment Adjusted EBITDA Expense (3) ​ 579,510 ​ ​ 312,861 ​ ​ 6,109 ​ ​ 28,026 ​ ​ (14,971) ​ 911,535 ​ Segment Adjusted EBITDA (4) ​ 306,592 ​ ​ 167,612 ​ ​ 32,432 ​ ​ 28,155 ​ ​ (6,721) ​ 528,070 ​ Total assets ​ 1,418,008 ​ ​ 493,133 ​ ​ 647,480 ​ ​ 561,171 ​ ​ (492,703) ​ 2,627,089 ​ Capital expenditures (5) ​ 157,759 ​ ​ 79,389 ​ ​ — ​ ​ 3,994 ​ ​ — ​ 241,142 ​ (1) The elimination column represents the elimination of intercompany transactions and is primarily comprised of sales from the Matrix Group to our mining operations, coal sales and purchases between operations within different segments, sales of receivables to AROP Funding, financing between segments and insurance premiums paid to Wildcat Insurance. ​ (2) Revenues included in the Other and Corporate column are primarily attributable to the Matrix Group revenues, administrative service revenues from affiliates, Wildcat Insurance revenues and brokerage coal sales. ​ (3) 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, ​ ​ ​ 2020 2019 2020 2019 ​ ​ (in thousands) ​ Segment Adjusted EBITDA Expense ​ $ 216,750 ​ $ 289,081 ​ $ 638,989 ​ $ 911,535 ​ Outside coal purchases ​ — ​ (10,599) ​ — ​ (15,910) ​ Other expense ​ (723) ​ (228) ​ (1,456) ​ (370) ​ Operating expenses (excluding depreciation, depletion and amortization) ​ $ 216,027 ​ $ 278,254 ​ $ 637,533 ​ $ 895,255 ​ ​ (4) 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, settlement gain, asset and goodwill impairments and acquisition gain. 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, ​ ​ ​ 2020 2019 2020 2019 ​ ​ (in thousands) ​ Consolidated Segment Adjusted EBITDA ​ $ 132,701 ​ $ 156,163 ​ $ 306,458 ​ $ 528,070 ​ General and administrative ​ (13,871) ​ (17,885) ​ (41,131) ​ (55,218) ​ Depreciation, depletion and amortization ​ (80,182) ​ (72,348) ​ (237,662) ​ (220,400) ​ Asset impairments ​ — ​ (15,190) ​ (24,977) ​ (15,190) ​ Goodwill impairment ​ ​ — ​ ​ — ​ ​ (132,026) ​ ​ — ​ Interest expense, net ​ (11,156) ​ (11,606) ​ (34,799) ​ (33,510) ​ Acquisition gain ​ ​ — ​ ​ — ​ ​ — ​ ​ 177,043 ​ Income tax expense ​ (293) ​ (50) ​ (111) ​ (130) ​ Acquisition gain attributable to noncontrolling interest ​ ​ — ​ ​ — ​ ​ — ​ ​ (7,083) ​ Net income (loss) attributable to ARLP ​ $ 27,199 ​ $ 39,084 ​ $ (164,248) ​ $ 373,582 ​ Noncontrolling interest ​ ​ 36 ​ ​ 117 ​ ​ 97 ​ ​ 7,407 ​ Net income (loss) ​ $ 27,235 ​ $ 39,201 ​ $ (164,151) ​ $ 380,989 ​ ​ (5) Capital Expenditures shown exclude the AllDale Acquisition which occurred in January 2019 and Wing Acquisition whic h occurred in August 2019 .

ORGANIZATION AND PRESENTATION (

ORGANIZATION AND PRESENTATION (Policies)	9 Months Ended
	Sep. 30, 2020
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, 2020 and December 31, 2019, the results of our operations and comprehensive income for the three and nine months ended September 30, 2020 and 2019, and cash flows for the nine months ended September 30, 2020 and 2019. 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 of 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, 2019. ​ 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, 2020. ​
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.
New Accounting Standards	​ New Accounting Standards Issued and Adopted ​ In August 2018, the FASB issued ASU 2018-13, Fair Value Measurement (Topic 820): Disclosure Framework – Changes to the Disclosure Requirement for Fair Value Measurement. ASU 2018-13 amended the fair value measurement guidance by removing and modifying certain disclosure requirements, while also adding new disclosure requirements including the requirement to disclose the range and weighted average of significant unobservable inputs used to develop certain Level 3 measurements. These changes are to be applied prospectively for only the most recent interim or annual period presented in the year of adoption. We adopted ASU 2018-13 on January 1, 2020. ​ In June 2016, the FASB issued ASU 2016-13, Financial Instruments–Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments

ACQUISITION (Tables)

ACQUISITION (Tables)	9 Months Ended
	Sep. 30, 2020
ACQUISITION
Summary of fair value allocation of assets acquired and liabilities assumed	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ As Previously ​ ​ ​ ​ ​ ​ ​ ​ Reported ​ Adjustments ​ Final ​ ​ ​ ​ ​ (in thousands) ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Mineral interests in proved properties ​ $ 58,084 ​ ​ 16,987 ​ $ 75,071 ​ Mineral interests in unproved properties ​ ​ 84,976 ​ ​ (17,275) ​ ​ 67,701 ​ Receivables ​ ​ 1,867 ​ ​ 288 ​ ​ 2,155 ​ Net assets acquired ​ $ 144,927 ​ ​ ​ ​ $ 144,927 ​

INVENTORIES (Tables)

INVENTORIES (Tables)	9 Months Ended
	Sep. 30, 2020
INVENTORIES
Schedule of inventories	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ September 30, ​ December 31, ​ ​ ​ 2020 2019 ​ ​ (in thousands) ​ ​ ​ ​ ​ ​ ​ ​ ​ Coal ​ $ 38,531 ​ $ 63,645 ​ Supplies (net of reserve for obsolescence of $5,577 and $5,555, respectively) ​ 36,348 ​ 37,660 ​ Total inventories, net ​ $ 74,879 ​ $ 101,305 ​

FAIR VALUE MEASUREMENTS (Tables

FAIR VALUE MEASUREMENTS (Tables)	9 Months Ended
	Sep. 30, 2020
FAIR VALUE MEASUREMENTS
Summary of fair value measurements within the hierarchy	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ September 30, 2020 ​ December 31, 2019 ​ ​ Level 1 Level 2 Level 3 Level 1 Level 2 Level 3 ​ ​ (in thousands) ​ Long-term debt ​ $ — ​ $ 494,712 ​ $ — ​ $ — ​ $ 736,206 ​ $ — ​ Total ​ $ — ​ $ 494,712 ​ $ — ​ $ — ​ $ 736,206 ​ $ — ​

LONG-TERM DEBT (Tables)

LONG-TERM DEBT (Tables)	9 Months Ended
	Sep. 30, 2020
LONG-TERM DEBT
Schedule of long-term debt	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Unamortized Discount and ​ ​ ​ Principal ​ Debt Issuance Costs ​ ​ ​ September 30, ​ December 31, ​ September 30, ​ December 31, ​ ​ 2020 2019 2020 2019 ​ ​ (in thousands) ​ Revolving credit facility ​ $ 135,000 ​ $ 255,000 ​ $ (7,280) ​ $ (3,050) ​ Senior notes ​ 400,000 ​ 400,000 ​ (4,192) ​ (4,879) ​ Securitization facility ​ ​ 72,200 ​ ​ 73,800 ​ ​ — ​ ​ — ​ May 2019 equipment financing ​ ​ 5,785 ​ ​ 8,199 ​ ​ — ​ ​ — ​ November 2019 equipment financing ​ ​ 44,890 ​ ​ 52,281 ​ ​ — ​ ​ — ​ June 2020 equipment financing ​ ​ 13,887 ​ ​ — ​ ​ — ​ ​ — ​ ​ ​ 671,762 ​ 789,280 ​ (11,472) ​ (7,929) ​ Less current maturities ​ (89,271) ​ (13,157) ​ — ​ — ​ Total long-term debt ​ $ 582,491 ​ $ 776,123 ​ $ (11,472) ​ $ (7,929) ​

VARIABLE INTEREST ENTITIES (Tab

VARIABLE INTEREST ENTITIES (Tables)	9 Months Ended
	Sep. 30, 2020
VARIABLE INTEREST ENTITIES
Schedule of distributions	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Alliance ​ Bluegrass ​ ​ ​ Minerals ​ Minerals ​ ​ ​ (in thousands) ​ Contributions ​ $ 143,112 ​ $ 5,963 ​ Distributions ​ ​ 86,384 ​ ​ 3,598 ​

INVESTMENTS (Tables)

INVESTMENTS (Tables)	9 Months Ended
	Sep. 30, 2020
INVESTMENTS
Schedule of changes in equity method investment	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Three Months Ended ​ Nine Months Ended ​ ​ ​ September 30, ​ September 30, ​ ​ 2020 2019 2020 2019 ​ ​ ​ (in thousands) ​ Beginning balance ​ $ 27,705 ​ $ 28,672 ​ $ 28,529 ​ $ 28,974 ​ Equity method investment income ​ ​ 62 ​ ​ 659 ​ ​ 650 ​ ​ 1,533 ​ Distributions received ​ ​ (352) ​ ​ (610) ​ ​ (1,491) ​ ​ (1,786) ​ Other ​ ​ — ​ ​ — ​ ​ (273) ​ ​ — ​ Ending balance ​ $ 27,415 ​ $ 28,721 ​ $ 27,415 ​ $ 28,721 ​

PARTNERS' CAPITAL (Tables)

PARTNERS' CAPITAL (Tables)	9 Months Ended
	Sep. 30, 2020
PARTNERS' CAPITAL
Summary of quarterly per unit distribution paid	​ ​ ​ ​ ​ ​ ​ ​ ​ Payment Date Per Unit Cash Distribution Total Cash Distribution ​ ​ ​ ​ ​ (in thousands) ​ ​ ​ ​ ​ ​ ​ ​ ​ February 14, 2019 ​ $ 0.5300 ​ $ 69,011 ​ May 15, 2019 ​ ​ 0.5350 ​ ​ 69,489 ​ August 14, 2019 ​ ​ 0.5400 ​ ​ 70,153 ​ November 14, 2019 ​ ​ 0.5400 ​ ​ 69,772 ​ Total ​ $ 2.1450 ​ $ 278,425 ​ ​ ​ ​ ​ ​ ​ ​ ​ February 14, 2020 ​ $ 0.4000 ​ $ 51,753 ​ Total ​ $ 0.4000 ​ $ 51,753 ​
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, 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 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Accumulated ​ ​ ​ ​ ​ ​ ​ ​ ​ Number of ​ Limited ​ Other ​ ​ ​ ​ ​ ​ ​ ​ ​ Limited Partner ​ Partners' ​ Comprehensive ​ Noncontrolling ​ Total Partners' ​ ​ Units Capital Loss Interest Capital ​ ​ (in thousands, except unit data) ​ Balance at January 1, 2019 128,095,511 ​ $ 1,229,268 ​ $ (46,871) ​ $ 5,290 ​ $ 1,187,687 ​ Comprehensive income: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Net income — ​ 276,428 ​ — ​ ​ 7,176 283,604 ​ Actuarially determined long-term liability adjustments — ​ — ​ (3,584) ​ — (3,584) ​ Total comprehensive income ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 280,020 ​ Settlement of deferred compensation plans 596,650 ​ (7,817) ​ ​ — ​ ​ — ​ ​ (7,817) ​ Purchase of units under unit repurchase program (300,970) ​ (5,251) ​ ​ — ​ ​ — ​ ​ (5,251) ​ Common unit-based compensation — ​ 2,743 ​ ​ — ​ ​ — ​ ​ 2,743 ​ Distributions on deferred common unit-based compensation — ​ (1,280) ​ ​ — ​ ​ — ​ ​ (1,280) ​ Distributions from consolidated company to noncontrolling interest ​ — ​ ​ — ​ ​ — ​ ​ (262) ​ ​ (262) ​ Distributions to Partners — ​ ​ (67,731) ​ ​ — ​ ​ — ​ ​ (67,731) ​ Balance at March 31, 2019 128,391,191 ​ ​ 1,426,360 ​ ​ (50,455) ​ ​ 12,204 ​ ​ 1,388,109 ​ Comprehensive income: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Net income — ​ 58,070 ​ — ​ ​ 114 58,184 ​ Actuarially determined long-term liability adjustments — ​ — ​ (118) ​ — (118) ​ Total comprehensive income ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 58,066 ​ Common unit-based compensation — ​ 3,021 ​ ​ — ​ ​ — ​ ​ 3,021 ​ Distributions on deferred common unit-based compensation — ​ (799) ​ ​ — ​ ​ — ​ ​ (799) ​ Distributions from consolidated company to noncontrolling interest ​ — ​ ​ — ​ ​ — ​ ​ (228) ​ ​ (228) ​ Distributions to Partners — ​ ​ (68,690) ​ ​ — ​ ​ — ​ ​ (68,690) ​ Balance at June 30, 2019 128,391,191 ​ ​ 1,417,962 ​ ​ (50,573) ​ ​ 12,090 ​ ​ 1,379,479 ​ Comprehensive income: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Net income — ​ 39,084 ​ — ​ ​ 117 39,201 ​ Actuarially determined long-term liability adjustments — ​ — ​ (119) ​ — (119) ​ Total comprehensive income ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 39,082 ​ Common unit-based compensation — ​ 3,066 ​ ​ — ​ ​ — ​ ​ 3,066 ​ Distributions on deferred common unit-based compensation — ​ (822) ​ ​ — ​ ​ — ​ ​ (822) ​ Distributions from consolidated company to noncontrolling interest ​ — ​ ​ — ​ ​ — ​ ​ (183) ​ ​ (183) ​ Distributions to Partners — ​ ​ (69,331) ​ ​ — ​ ​ — ​ ​ (69,331) ​ Balance at September 30, 2019 128,391,191 ​ $ 1,389,959 ​ $ (50,692) ​ $ 12,024 ​ $ 1,351,291 ​

REVENUE FROM CONTRACTS WITH C_2

REVENUE FROM CONTRACTS WITH CUSTOMERS (Tables)	9 Months Ended
	Sep. 30, 2020
REVENUE FROM CONTRACTS WITH CUSTOMERS
Schedule of disaggregation of revenues by type	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Illinois ​ ​ Other and ​ ​ ​ ​ ​ Basin Appalachia Minerals Corporate Elimination Consolidated ​ ​ ​ (in thousands) ​ Three Months Ended September 30, 2020 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Coal sales ​ $ 206,356 ​ $ 129,411 ​ $ — ​ $ — ​ $ — ​ $ 335,767 ​ Oil & gas royalties ​ ​ — ​ ​ — ​ ​ 9,693 ​ ​ — ​ ​ — ​ ​ 9,693 ​ Transportation revenues ​ ​ 3,722 ​ ​ 2,504 ​ ​ — ​ ​ — ​ ​ — ​ ​ 6,226 ​ Other revenues ​ ​ 282 ​ ​ 395 ​ ​ 28 ​ ​ 6,070 ​ ​ (2,810) ​ ​ 3,965 ​ Total revenues ​ $ 210,360 ​ $ 132,310 ​ $ 9,721 ​ $ 6,070 ​ $ (2,810) ​ $ 355,651 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Three Months Ended September 30, 2019 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Coal sales ​ $ 256,293 ​ $ 162,316 ​ $ — ​ $ 5,689 ​ $ (4,293) ​ $ 420,005 ​ Oil & gas royalties ​ ​ — ​ ​ — ​ ​ 13,969 ​ ​ — ​ ​ — ​ ​ 13,969 ​ Transportation revenues ​ ​ 18,778 ​ ​ 1,246 ​ ​ — ​ ​ — ​ ​ — ​ ​ 20,024 ​ Other revenues ​ ​ 5,264 ​ ​ 852 ​ ​ 208 ​ ​ 7,434 ​ ​ (3,030) ​ ​ 10,728 ​ Total revenues ​ $ 280,335 ​ $ 164,414 ​ $ 14,177 ​ $ 13,123 ​ $ (7,323) ​ $ 464,726 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Nine Months Ended September 30, 2020 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Coal sales ​ $ 539,614 ​ $ 347,076 ​ $ — ​ $ — ​ $ — ​ $ 886,690 ​ Oil & gas royalties ​ ​ — ​ ​ — ​ ​ 31,718 ​ ​ — ​ ​ — ​ ​ 31,718 ​ Transportation revenues ​ ​ 10,731 ​ ​ 5,991 ​ ​ — ​ ​ — ​ ​ — ​ ​ 16,722 ​ Other revenues ​ ​ 1,674 ​ ​ 14,456 ​ ​ 113 ​ ​ 18,409 ​ ​ (8,166) ​ ​ 26,486 ​ Total revenues ​ $ 552,019 ​ $ 367,523 ​ $ 31,831 ​ $ 18,409 ​ $ (8,166) ​ $ 961,616 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Nine Months Ended September 30, 2019 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Coal sales ​ $ 875,544 ​ $ 477,720 ​ $ — ​ $ 16,530 ​ $ (12,463) ​ $ 1,357,331 ​ Oil & gas royalties ​ ​ — ​ ​ — ​ ​ 36,254 ​ ​ — ​ ​ — ​ ​ 36,254 ​ Transportation revenues ​ ​ 79,303 ​ ​ 3,589 ​ ​ — ​ ​ — ​ ​ — ​ ​ 82,892 ​ Other revenues ​ ​ 10,557 ​ ​ 2,753 ​ ​ 1,079 ​ ​ 26,745 ​ ​ (9,229) ​ ​ 31,905 ​ Total revenues ​ $ 965,404 ​ $ 484,062 ​ $ 37,333 ​ $ 43,275 ​ $ (21,692) ​ $ 1,508,382 ​
Schedule of current coal supply contracts allocated to performance obligations that are unsatisfied or partially unsatisfied	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 2023 and ​ ​ ​ ​ 2020 2021 2022 Thereafter Total ​ ​ (in thousands) ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Illinois Basin coal revenues ​ $ 248,362 ​ $ 618,966 ​ $ 238,514 ​ $ 307,695 ​ $ 1,413,537 ​ Appalachia coal revenues ​ ​ 138,340 ​ ​ 130,075 ​ ​ 57,891 ​ ​ — ​ ​ 326,306 ​ Total coal revenues (1) ​ $ 386,702 ​ $ 749,041 ​ $ 296,405 ​ $ 307,695 ​ $ 1,739,843 ​ (1) Coal revenues generally consists of consolidated revenues excluding our Minerals segment .

EARNINGS PER LIMITED PARTNER _2

EARNINGS PER LIMITED PARTNER UNIT (Tables)	9 Months Ended
	Sep. 30, 2020
EARNINGS PER LIMITED PARTNER UNIT
Reconciliation of net income and EPU calculations	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Three Months Ended ​ Nine Months Ended ​ ​ ​ September 30, ​ September 30, ​ ​ 2020 2019 2020 2019 ​ ​ (in thousands, except per unit data) ​ Net income (loss) attributable to ARLP ​ $ 27,199 ​ $ 39,084 ​ $ (164,248) ​ $ 373,582 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Less: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Distributions to participating securities ​ — ​ (1,133) ​ — ​ (3,360) ​ Undistributed earnings attributable to participating securities ​ (581) ​ — ​ — ​ (2,655) ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Net income (loss) attributable to ARLP available to limited partners ​ $ 26,618 ​ $ 37,951 ​ $ (164,248) ​ $ 367,567 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted-average limited partner units outstanding – basic and diluted ​ 127,195 ​ 128,391 ​ 127,154 ​ 128,312 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Earnings per limited partner unit - basic and diluted (1) ​ $ 0.21 ​ $ 0.30 ​ $ (1.29) ​ $ 2.86 ​ (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 661 and 656 for the three and nine months ended September 30, 2020, respectively, and 1,133 and 1,216 for the three and nine months ended September 30, 2019, 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, 2020
Accrued Workers Compensation And Pneumoconiosis Benefits
Reconciliation of changes in workers' compensation liability	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Three Months Ended ​ Nine Months Ended ​ ​ September 30, ​ September 30, ​ ​ ​ 2020 2019 2020 2019 ​ ​ ​ (in thousands) ​ Beginning balance ​ $ 54,478 ​ $ 53,425 ​ $ 53,384 ​ $ 49,539 ​ Accruals increase ​ 1,599 ​ 2,395 ​ 3,539 ​ 6,603 ​ Payments ​ (2,123) ​ (2,663) ​ (6,686) ​ (8,588) ​ Interest accretion ​ 319 ​ 402 ​ 958 ​ 1,204 ​ Valuation loss (1) ​ — ​ — ​ 3,078 ​ 4,801 ​ Ending balance ​ $ 54,273 ​ $ 53,559 ​ $ 54,273 ​ $ 53,559 ​ (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. We conducted a 2020 mid-year review of our actuarial assumptions which resulted in a valuation loss due to unfavorable changes in claims development and a decrease in the discount rate from 2.81% to 2.05% . Our 2019 mid-year actuarial review resulted in a valuation loss due to unfavorable changes in claims development and a decrease in the discount rate from 3.89% to 3.06% .
Pneumoconiosis benefits
Accrued Workers Compensation And Pneumoconiosis Benefits
Components of net periodic benefit cost	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Three Months Ended ​ Nine Months Ended ​ ​ ​ September 30, ​ September 30, ​ ​ ​ 2020 2019 2020 2019 ​ ​ (in thousands) ​ Service cost ​ $ 882 ​ $ 656 ​ $ 2,643 ​ $ 1,947 Interest cost (1) ​ 750 ​ 761 ​ 2,249 ​ 2,283 ​ Net amortization (1) ​ (172) ​ (1,145) ​ (515) ​ (3,436) ​ Net periodic benefit cost ​ $ 1,460 ​ $ 272 ​ $ 4,377 ​ $ 794 ​ (1) Interest cost and net amortization are included in the Other expense line item within our condensed consolidated statements of income.

COMPENSATION PLANS (Tables)

COMPENSATION PLANS (Tables)	9 Months Ended
	Sep. 30, 2020
ARLP LTIP
Compensation Plans
Summary of activity in share-based plans	​ ​ ​ ​ ​ ​ ​ ​ ​ Number of units Weighted average grant date fair value per unit ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Non-vested grants at January 1, 2020 ​ 1,603,378 ​ ​ ​ ​ Granted 950,035 ​ $ 9.62 ​ Vested (1) (424,486) ​ 23.22 ​ Forfeited (13,835) ​ 16.13 ​ Non-vested grants at September 30, 2020 (2) 2,115,092 ​ ​ ​ (1) During the nine months ended September 30, 2020, we issued 279,622 unrestricted common units to the LTIP participants. The remaining vested units were settled in cash to satisfy tax withholding obligations of the LTIP participants. (2) Represents total non-vested grants outstanding including 675,302 restricted units that were granted in 2019 (the "2019 Grants"). During the First Quarter, it was determined that the vesting requirements for the 2019 Grants were not probable of being satisfied.
SERP and Directors' Compensation Plans
Compensation Plans
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, 2020 ​ 631,365 ​ $ 25.48 ​ $ 6,831 ​ Granted ​ 29,544 ​ ​ 7.87 ​ ​ ​ ​ Phantom units outstanding as of September 30, 2020 660,909 ​ 24.69 ​ ​ 1,831 ​

COMPONENTS OF PENSION PLAN NE_2

COMPONENTS OF PENSION PLAN NET PERIODIC BENEFIT COSTS (Tables)	9 Months Ended
	Sep. 30, 2020
Defined benefit pension plan
Employee Benefit Plans
Components of net periodic benefit cost	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Three Months Ended ​ Nine Months Ended ​ ​ ​ September 30, ​ September 30, ​ ​ ​ 2020 2019 2020 2019 ​ ​ (in thousands) ​ Interest cost ​ $ 1,030 ​ $ 1,217 ​ $ 3,138 ​ $ 3,649 ​ Expected return on plan assets ​ (1,413) ​ (1,233) ​ (4,396) ​ (3,699) ​ Amortization of prior service cost ​ ​ 47 ​ ​ 46 ​ ​ 140 ​ ​ 139 ​ Amortization of net loss ​ 969 ​ 980 ​ 3,096 ​ 2,941 ​ Net periodic benefit cost (1) ​ $ 633 ​ $ 1,010 ​ $ 1,978 ​ $ 3,030 ​ (1) Net periodic benefit cost for the Pension Plan is included in the Other expense line item within our condensed consolidated statements of income.

SEGMENT INFORMATION (Tables)

SEGMENT INFORMATION (Tables)	9 Months Ended
	Sep. 30, 2020
SEGMENT INFORMATION
Schedule of reportable segment results	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Illinois ​ ​ Other and Elimination ​ ​ ​ Basin Appalachia Minerals Corporate (1) Consolidated ​ ​ (in thousands) Three Months Ended September 30, 2020 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Revenues - Outside ​ $ 210,360 ​ $ 132,310 ​ $ 9,721 ​ $ 3,260 ​ $ — ​ $ 355,651 ​ Revenues - Intercompany ​ ​ — ​ ​ — ​ ​ — ​ ​ 2,810 ​ ​ (2,810) ​ ​ — ​ Total revenues (2) ​ ​ 210,360 ​ ​ 132,310 ​ ​ 9,721 ​ ​ 6,070 ​ ​ (2,810) ​ ​ 355,651 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Segment Adjusted EBITDA Expense (3) ​ 125,021 ​ 86,447 ​ 849 ​ 4,908 ​ (475) ​ 216,750 ​ Segment Adjusted EBITDA (4) ​ 81,617 ​ 43,358 ​ 8,898 ​ 1,163 ​ (2,335) ​ 132,701 ​ Capital expenditures ​ 3,815 ​ 14,541 ​ — ​ 219 ​ — ​ 18,575 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Three Months Ended September 30, 2019 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Revenues - Outside ​ $ 276,042 ​ $ 164,414 ​ $ 14,177 ​ $ 10,093 ​ $ — ​ $ 464,726 ​ Revenues - Intercompany ​ ​ 4,293 ​ ​ — ​ ​ — ​ ​ 3,030 ​ ​ (7,323) ​ ​ — ​ Total revenues (2) ​ ​ 280,335 ​ ​ 164,414 ​ ​ 14,177 ​ ​ 13,123 ​ ​ (7,323) ​ ​ 464,726 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Segment Adjusted EBITDA Expense (3) ​ 173,779 ​ 107,990 ​ 2,517 ​ 9,878 ​ (5,083) ​ 289,081 ​ Segment Adjusted EBITDA (4) ​ 87,780 ​ 55,178 ​ 12,202 ​ 3,243 ​ (2,240) ​ 156,163 ​ Capital expenditures ​ 49,829 ​ 25,056 ​ — ​ 630 ​ — ​ 75,515 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Nine Months Ended September 30, 2020 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Revenues - Outside ​ $ 552,019 ​ $ 367,523 ​ $ 31,831 ​ $ 10,243 ​ $ — ​ $ 961,616 ​ Revenues - Intercompany ​ ​ — ​ ​ — ​ ​ — ​ ​ 8,166 ​ ​ (8,166) ​ ​ — ​ Total revenues (2) ​ ​ 552,019 ​ ​ 367,523 ​ ​ 31,831 ​ ​ 18,409 ​ ​ (8,166) ​ ​ 961,616 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Segment Adjusted EBITDA Expense (3) ​ 383,486 ​ ​ 240,116 ​ ​ 2,851 ​ ​ 13,697 ​ ​ (1,161) ​ 638,989 ​ Segment Adjusted EBITDA (4) ​ 157,803 ​ ​ 121,416 ​ ​ 29,534 ​ ​ 4,710 ​ ​ (7,005) ​ 306,458 ​ Total assets ​ 1,082,992 ​ ​ 470,261 ​ ​ 616,491 ​ ​ 468,590 ​ ​ (406,994) ​ 2,231,340 ​ Capital expenditures ​ 44,073 ​ ​ 57,798 ​ ​ — ​ ​ 949 ​ ​ — ​ 102,820 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Nine Months Ended September 30, 2019 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Revenues - Outside ​ $ 952,941 ​ $ 484,062 ​ $ 37,333 ​ $ 34,046 ​ $ — ​ $ 1,508,382 ​ Revenues - Intercompany ​ ​ 12,463 ​ ​ — ​ ​ — ​ ​ 9,229 ​ ​ (21,692) ​ ​ — ​ Total revenues (2) ​ ​ 965,404 ​ ​ 484,062 ​ ​ 37,333 ​ ​ 43,275 ​ ​ (21,692) ​ ​ 1,508,382 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Segment Adjusted EBITDA Expense (3) ​ 579,510 ​ ​ 312,861 ​ ​ 6,109 ​ ​ 28,026 ​ ​ (14,971) ​ 911,535 ​ Segment Adjusted EBITDA (4) ​ 306,592 ​ ​ 167,612 ​ ​ 32,432 ​ ​ 28,155 ​ ​ (6,721) ​ 528,070 ​ Total assets ​ 1,418,008 ​ ​ 493,133 ​ ​ 647,480 ​ ​ 561,171 ​ ​ (492,703) ​ 2,627,089 ​ Capital expenditures (5) ​ 157,759 ​ ​ 79,389 ​ ​ — ​ ​ 3,994 ​ ​ — ​ 241,142 ​ (1) The elimination column represents the elimination of intercompany transactions and is primarily comprised of sales from the Matrix Group to our mining operations, coal sales and purchases between operations within different segments, sales of receivables to AROP Funding, financing between segments and insurance premiums paid to Wildcat Insurance. ​ (2) Revenues included in the Other and Corporate column are primarily attributable to the Matrix Group revenues, administrative service revenues from affiliates, Wildcat Insurance revenues and brokerage coal sales. ​ (3) 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, ​ ​ ​ 2020 2019 2020 2019 ​ ​ (in thousands) ​ Segment Adjusted EBITDA Expense ​ $ 216,750 ​ $ 289,081 ​ $ 638,989 ​ $ 911,535 ​ Outside coal purchases ​ — ​ (10,599) ​ — ​ (15,910) ​ Other expense ​ (723) ​ (228) ​ (1,456) ​ (370) ​ Operating expenses (excluding depreciation, depletion and amortization) ​ $ 216,027 ​ $ 278,254 ​ $ 637,533 ​ $ 895,255 ​ ​ (4) 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, settlement gain, asset and goodwill impairments and acquisition gain. 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, ​ ​ ​ 2020 2019 2020 2019 ​ ​ (in thousands) ​ Consolidated Segment Adjusted EBITDA ​ $ 132,701 ​ $ 156,163 ​ $ 306,458 ​ $ 528,070 ​ General and administrative ​ (13,871) ​ (17,885) ​ (41,131) ​ (55,218) ​ Depreciation, depletion and amortization ​ (80,182) ​ (72,348) ​ (237,662) ​ (220,400) ​ Asset impairments ​ — ​ (15,190) ​ (24,977) ​ (15,190) ​ Goodwill impairment ​ ​ — ​ ​ — ​ ​ (132,026) ​ ​ — ​ Interest expense, net ​ (11,156) ​ (11,606) ​ (34,799) ​ (33,510) ​ Acquisition gain ​ ​ — ​ ​ — ​ ​ — ​ ​ 177,043 ​ Income tax expense ​ (293) ​ (50) ​ (111) ​ (130) ​ Acquisition gain attributable to noncontrolling interest ​ ​ — ​ ​ — ​ ​ — ​ ​ (7,083) ​ Net income (loss) attributable to ARLP ​ $ 27,199 ​ $ 39,084 ​ $ (164,248) ​ $ 373,582 ​ Noncontrolling interest ​ ​ 36 ​ ​ 117 ​ ​ 97 ​ ​ 7,407 ​ Net income (loss) ​ $ 27,235 ​ $ 39,201 ​ $ (164,151) ​ $ 380,989 ​ ​ (5) Capital Expenditures shown exclude the AllDale Acquisition which occurred in January 2019 and Wing Acquisition whic h occurred in August 2019 .

ACQUISITION - Assets and Liabil

ACQUISITION - Assets and Liabilities (Details) - Wing $ in Thousands	Aug. 02, 2019USD ($)a	Sep. 30, 2020USD ($)
ACQUISITION
Royalty acres, net | a	9,000
Royalty acres, gross | a	400,000
Cash	$ 144,900
Assets acquired and liabilities assumed
Mineral interests in proved properties	75,071
Mineral interests in unproved properties	67,701
Receivables	2,155
Net assets acquired	144,927
Previously Reported
Assets acquired and liabilities assumed
Mineral interests in proved properties	58,084
Mineral interests in unproved properties	84,976
Receivables	1,867
Net assets acquired	144,927
Adjustments
Assets acquired and liabilities assumed
Mineral interests in proved properties	16,987
Mineral interests in unproved properties	(17,275)
Receivables	$ 288	$ 300

LONG-LIVED ASSET IMPAIRMENTS (D

LONG-LIVED ASSET IMPAIRMENTS (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019	Aug. 16, 2019	Aug. 15, 2019
Asset impairment charges
Asset impairments	$ 15,190	$ 24,977	$ 15,190
Property, plant and equipment		1,860,922		$ 2,008,986
Illinois Basin
Asset impairment charges
Asset impairments		$ 25,000	$ 15,200
Property, plant and equipment					$ 25,800	$ 35,900
Accrued payments					$ 5,100

GOODWILL IMPAIRMENT (Details)

GOODWILL IMPAIRMENT (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2020	Dec. 31, 2019
GOODWILL IMPAIRMENT
Goodwill	$ 4,373	$ 136,399
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, 2020	Dec. 31, 2019
INVENTORIES
Coal	$ 38,531	$ 63,645
Supplies (net of reserve for obsolescence of $5,577 and $5,555, respectively)	36,348	37,660
Total inventories, net	74,879	101,305
Reserve for obsolescence	$ 5,577	$ 5,555

FAIR VALUE MEASUREMENTS (Detail

FAIR VALUE MEASUREMENTS (Details) - Estimated fair value - Significant Observable Inputs (Level 2) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
FAIR VALUE MEASUREMENTS
Long-term debt	$ 494,712	$ 736,206
Total	$ 494,712	$ 736,206

LONG-TERM DEBT - Components (De

LONG-TERM DEBT - Components (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Principal
Aggregate maturities of long-term debt	$ 671,762	$ 789,280
Less current maturities	(89,271)	(13,157)
Total long-term debt	582,491	776,123
Unamortized Discount and Debt Issuance Costs
Unamortized debt issuance costs including current and non-current	(11,472)	(7,929)
Total unamortized debt issuance costs	(11,472)	(7,929)
Revolving credit facility
Principal
Aggregate maturities of long-term debt	135,000	255,000
Unamortized Discount and Debt Issuance Costs
Unamortized debt issuance costs including current and non-current	(7,280)	(3,050)
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	(4,192)	(4,879)
Securitization Facility
Principal
Aggregate maturities of long-term debt	72,200	73,800
May 2019 equipment financing
Principal
Aggregate maturities of long-term debt	5,785	8,199
November 2019 equipment financing
Principal
Aggregate maturities of long-term debt	44,890	$ 52,281
June 2020 equipment financing
Principal
Aggregate maturities of long-term debt	$ 13,887

LONG-TERM DEBT - Credit Facilit

LONG-TERM DEBT - Credit Facility (Details) $ in Thousands	Mar. 09, 2020USD ($)item	Sep. 30, 2020USD ($)	Jan. 27, 2017USD ($)
Long-Term Debt
Debt issuance costs incurred		$ 5,821
Credit Agreement
Long-Term Debt
Maximum borrowing capacity	$ 537,750
Number of benchmarks | item	3
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
ARLP debt arrangements requirements, period over which the ratios are required to be maintained	12 months
Actual debt to cash flow ratio for trailing twelve months		1.69
Actual cash flow to interest expense ratio for trailing twelve months		8.22
Credit Agreement | Eurodollar Rate
Long-Term Debt
Effective interest rate (as a percent)		3.01%
Credit Agreement | Extended Commitment to May 23, 2021
Long-Term Debt
Maximum borrowing capacity	$ 459,500
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		0.69
Revolving credit facility
Long-Term Debt
Line of credit facility, available for borrowing		$ 381,000
Annual commitment fee percentage, undrawn portion		0.35%
Letters of credit subfacility
Long-Term Debt
Maximum borrowing capacity	$ 125,000
Letters of credit outstanding		$ 21,800
Swingline subfacility
Long-Term Debt
Maximum borrowing capacity	$ 15,000
Fourth Amended and Restated Credit Agreement
Long-Term Debt
Maximum borrowing capacity			$ 494,750

LONG-TERM DEBT - 2025 Senior No

LONG-TERM DEBT - 2025 Senior Notes (Details) - USD ($) $ in Thousands	Apr. 24, 2017	Sep. 30, 2020	Dec. 31, 2019
Issuance of Senior Notes
Discount and debt issuance costs incurred		$ 11,472	$ 7,929
Senior notes due 2025
Issuance of Senior Notes
Principal amount	$ 400,000
Term	8 years
Interest rate (as a percent)	7.50%
Discount and debt issuance costs incurred		$ 4,192	$ 4,879

LONG-TERM DEBT - Securitization

LONG-TERM DEBT - Securitization Facility (Details) - Securitization Facility - USD ($) $ in Millions	Sep. 30, 2020	Dec. 05, 2014
Long-Term Debt
Maximum borrowing capacity		$ 100
Facility outstanding amount	$ 72.2

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%

VARIABLE INTEREST ENTITIES - Ca

VARIABLE INTEREST ENTITIES - Cavalier (Details) - USD ($) $ in Thousands	Feb. 14, 2020	Nov. 14, 2019	Aug. 14, 2019	May 15, 2019	Feb. 14, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Variable Interest Entities
Distributions paid to Partners	$ 51,753	$ 69,772	$ 70,153	$ 69,489	$ 69,011	$ 51,753	$ 208,653	$ 278,425
Cavalier Minerals | Alliance Minerals
Variable Interest Entities
Contributions						143,112
Distributions paid to Partners						86,384
Cavalier Minerals | Bluegrass Minerals
Variable Interest Entities
Contributions						5,963
Distributions paid to Partners						$ 3,598
Cavalier Minerals | Bluegrass Minerals
Variable Interest Entities
Incentive distribution of available cash (as a percent)						25.00%
Cavalier Minerals | Bluegrass Minerals
Variable Interest Entities
Noncontrolling ownership interest (as a percent)						4.00%
Cavalier Minerals | Alliance Minerals
Variable Interest Entities
Ownership interest in VIE (as a percent)						96.00%

VARIABLE INTEREST ENTITIES - Al

VARIABLE INTEREST ENTITIES - All Dale III (Detail) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2020	Feb. 28, 2017
All Dale Minerals III
Equity Investments
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
Other Commitment		$ 30
All Dale Minerals III | All Dale Minerals III
Equity Investments
Ownership percentage by limited partners	13.90%

VARIABLE INTEREST ENTITIES - WK

VARIABLE INTEREST ENTITIES - WKY CoalPlay (Details) - WKY CoalPlay $ in Millions	9 Months Ended
	Sep. 30, 2020USD ($)
Variable Interest Entities
Payments made	$ 10.8
Percentage of internal rate of return on purchase price, if leased reserves acquired	7.00%

INVESTMENTS - AllDale (Details)

INVESTMENTS - AllDale (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Changes in equity method investment
Beginning balance			$ 28,529
Equity method investment income	$ 62	$ 659	650	$ 1,533
Ending balance	27,415		27,415
All Dale Minerals III
Changes in equity method investment
Beginning balance	27,705	28,672	28,529	28,974
Equity method investment income	62	659	650	1,533
Distributions received	(352)	(610)	(1,491)	(1,786)
Other			(273)
Ending balance	$ 27,415	$ 28,721	$ 27,415	$ 28,721

INVESTMENTS - Kodiak (Details)

INVESTMENTS - Kodiak (Details) - USD ($) $ in Thousands	Feb. 08, 2019	Sep. 30, 2019	Jul. 19, 2017
Equity securities without readily determinable fair value
Redemption of preferred interest		$ 134,288
Kodiak
Equity securities without readily determinable fair value
Equity securities	$ 0		$ 100,000
Redemption of preferred interest	135,000
Gain on redemption	$ 11,500

PARTNERS' CAPITAL - Distributio

PARTNERS' CAPITAL - Distributions (Details) - USD ($) $ / shares in Units, $ in Thousands	Feb. 14, 2020	Nov. 14, 2019	Aug. 14, 2019	May 15, 2019	Feb. 14, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
PARTNERS' CAPITAL
Quarterly distribution paid (in dollars per unit)	$ 0.4000	$ 0.5400	$ 0.5400	$ 0.5350	$ 0.5300	$ 0.4000		$ 2.1450
Total Cash Distribution	$ 51,753	$ 69,772	$ 70,153	$ 69,489	$ 69,011	$ 51,753	$ 208,653	$ 278,425

PARTNERS' CAPITAL - Narrative (

PARTNERS' CAPITAL - Narrative (Details) - USD ($) $ / shares in Units, $ in Millions	9 Months Ended	29 Months Ended
	Sep. 30, 2020	Sep. 30, 2020	May 31, 2018
Partners' capital
Repurchase and retire authorization			$ 100
Treasury units retired	$ 0
Number of units retired		5,460,639
Repurchase price (in dollars per unit)		$ 17.12
Simplification Transactions
Partners' capital
Number of units retired		35

PARTNERS' CAPITAL - Change (Det

PARTNERS' CAPITAL - Change (Details) - USD ($) $ in Thousands	3 Months Ended						9 Months Ended		29 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020
Increase (Decrease) in Partners's Capital
Balance at beginning of period	$ 1,023,152	$ 1,067,504	$ 1,265,424	$ 1,379,479	$ 1,388,109	$ 1,187,687	$ 1,265,424	$ 1,187,687
Balance at beginning of period (in units)			126,915,597				126,915,597
Comprehensive income (loss):
Net income (loss)	27,235	(46,679)	$ (144,707)	39,201	58,184	283,604	$ (164,151)	380,989
Actuarially determined long-term liability adjustments	844	939	938	(119)	(118)	(3,584)	2,721	(3,821)
COMPREHENSIVE INCOME (LOSS)	28,079	(45,740)	(143,769)	39,082	58,066	280,020	(161,430)	377,168
Settlement of deferred compensation plans			(1,310)			(7,817)
Purchase of units under unit repurchase program						(5,251)			$ (93,500)
Common unit-based compensation	1,645	1,610	(527)	3,066	3,021	2,743
Distributions on deferred common unit-based compensation			(986)	(822)	(799)	(1,280)
Distributions from consolidated company to noncontrolling interest	(93)	(222)	(288)	(183)	(228)	(262)
Distributions to Partners			(50,767)	(69,331)	(68,690)	(67,731)
Other			(273)
Balance at end of period	$ 1,052,783	1,023,152	1,067,504	1,351,291	1,379,479	1,388,109	$ 1,052,783	1,351,291	$ 1,052,783
Balance at end of period (in units)	127,195,219						127,195,219		127,195,219
Accumulated Other Comprehensive Income (Loss)
Increase (Decrease) in Partners's Capital
Balance at beginning of period	$ (76,116)	(77,055)	(77,993)	(50,573)	(50,455)	(46,871)	$ (77,993)	(46,871)
Comprehensive income (loss):
Actuarially determined long-term liability adjustments	844	939	938	(119)	(118)	(3,584)
Balance at end of period	(75,272)	(76,116)	(77,055)	(50,692)	(50,573)	(50,455)	(75,272)	(50,692)	$ (75,272)
Noncontrolling Interest
Increase (Decrease) in Partners's Capital
Balance at beginning of period	11,486	11,723	11,935	12,090	12,204	5,290	11,935	5,290
Comprehensive income (loss):
Net income (loss)	36	(15)	76	117	114	7,176
Distributions from consolidated company to noncontrolling interest	(93)	(222)	(288)	(183)	(228)	(262)
Balance at end of period	11,429	11,486	11,723	12,024	12,090	12,204	11,429	12,024	11,429
Limited Partners' Capital
Increase (Decrease) in Partners's Capital
Balance at beginning of period	$ 1,087,782	$ 1,132,836	$ 1,331,482	$ 1,417,962	$ 1,426,360	$ 1,229,268	$ 1,331,482	$ 1,229,268
Balance at beginning of period (in units)	127,195,219	127,195,219	126,915,597	128,391,191	128,391,191	128,095,511	126,915,597	128,095,511
Comprehensive income (loss):
Net income (loss)	$ 27,199	$ (46,664)	$ (144,783)	$ 39,084	$ 58,070	$ 276,428
Settlement of deferred compensation plans			$ (1,310)			$ (7,817)
Settlement of deferred compensation plans (in units)			279,622			596,650
Purchase of units under unit repurchase program						$ (5,251)
Purchase of units under unit repurchase program (in units)						(300,970)
Common unit-based compensation	1,645	1,610	$ (527)	3,066	3,021	$ 2,743
Distributions on deferred common unit-based compensation			(986)	(822)	(799)	(1,280)
Distributions to Partners			(50,767)	(69,331)	(68,690)	(67,731)
Other			(273)
Balance at end of period	$ 1,116,626	$ 1,087,782	$ 1,132,836	$ 1,389,959	$ 1,417,962	$ 1,426,360	$ 1,116,626	$ 1,389,959	$ 1,116,626
Balance at end of period (in units)	127,195,219	127,195,219	127,195,219	128,391,191	128,391,191	128,391,191	127,195,219	128,391,191	127,195,219

REVENUE FROM CONTRACTS WITH C_3

REVENUE FROM CONTRACTS WITH CUSTOMERS - Disaggregation of revenues (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Disaggregation of revenues
Revenues	$ 355,651	$ 464,726	$ 961,616	$ 1,508,382
Coal sales
Disaggregation of revenues
Revenues	335,767	420,005	886,690	1,357,331
Oil & gas royalties
Disaggregation of revenues
Revenues	9,693	13,969	31,718	36,254
Transportation revenues
Disaggregation of revenues
Revenues	6,226	20,024	16,722	82,892
Other revenues
Disaggregation of revenues
Revenues	3,965	10,728	26,486	31,905
Illinois Basin
Disaggregation of revenues
Revenues	210,360	280,335	552,019	965,404
Illinois Basin | Coal sales
Disaggregation of revenues
Revenues	206,356	256,293	539,614	875,544
Illinois Basin | Transportation revenues
Disaggregation of revenues
Revenues	3,722	18,778	10,731	79,303
Illinois Basin | Other revenues
Disaggregation of revenues
Revenues	282	5,264	1,674	10,557
Appalachia
Disaggregation of revenues
Revenues	132,310	164,414	367,523	484,062
Appalachia | Coal sales
Disaggregation of revenues
Revenues	129,411	162,316	347,076	477,720
Appalachia | Transportation revenues
Disaggregation of revenues
Revenues	2,504	1,246	5,991	3,589
Appalachia | Other revenues
Disaggregation of revenues
Revenues	395	852	14,456	2,753
Minerals
Disaggregation of revenues
Revenues	9,721	14,177	31,831	37,333
Minerals | Oil & gas royalties
Disaggregation of revenues
Revenues	9,693	13,969	31,718	36,254
Minerals | Other revenues
Disaggregation of revenues
Revenues	28	208	113	1,079
Other and Corporate
Disaggregation of revenues
Revenues	6,070	13,123	18,409	43,275
Other and Corporate | Coal sales
Disaggregation of revenues
Revenues		5,689		16,530
Other and Corporate | Other revenues
Disaggregation of revenues
Revenues	6,070	7,434	18,409	26,745
Elimination
Disaggregation of revenues
Revenues	(2,810)	(7,323)	(8,166)	(21,692)
Elimination | Coal sales
Disaggregation of revenues
Revenues		(4,293)		(12,463)
Elimination | Other revenues
Disaggregation of revenues
Revenues	(2,810)	(3,030)	(8,166)	(9,229)
Elimination | Illinois Basin
Disaggregation of revenues
Revenues		4,293		12,463
Elimination | Other and Corporate
Disaggregation of revenues
Revenues	$ 2,810	$ 3,030	$ 8,166	$ 9,229

REVENUE FROM CONTRACTS WITH C_4

REVENUE FROM CONTRACTS WITH CUSTOMERS - Coal supply contracts (Details) $ in Thousands	Sep. 30, 2020USD ($)
Performance obligations unsatisfied or partially unsatisfied
Total	$ 1,739,843
Illinois Basin
Performance obligations unsatisfied or partially unsatisfied
Total	1,413,537
Appalachia
Performance obligations unsatisfied or partially unsatisfied
Total	326,306
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2020-10-01
Performance obligations unsatisfied or partially unsatisfied
Total	$ 386,702
Expected timing of satisfaction period	3 months
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2020-10-01 | Illinois Basin
Performance obligations unsatisfied or partially unsatisfied
Total	$ 248,362
Expected timing of satisfaction period	3 months
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2020-10-01 | Appalachia
Performance obligations unsatisfied or partially unsatisfied
Total	$ 138,340
Expected timing of satisfaction period	3 months
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2021-01-01
Performance obligations unsatisfied or partially unsatisfied
Total	$ 749,041
Expected timing of satisfaction period	1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2021-01-01 | Illinois Basin
Performance obligations unsatisfied or partially unsatisfied
Total	$ 618,966
Expected timing of satisfaction period	1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2021-01-01 | Appalachia
Performance obligations unsatisfied or partially unsatisfied
Total	$ 130,075
Expected timing of satisfaction period	1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2022-01-01
Performance obligations unsatisfied or partially unsatisfied
Total	$ 296,405
Expected timing of satisfaction period	1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2022-01-01 | Illinois Basin
Performance obligations unsatisfied or partially unsatisfied
Total	$ 238,514
Expected timing of satisfaction period	1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2022-01-01 | Appalachia
Performance obligations unsatisfied or partially unsatisfied
Total	$ 57,891
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	$ 307,695
Expected timing of satisfaction period
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2023-01-01 | Illinois Basin
Performance obligations unsatisfied or partially unsatisfied
Total	$ 307,695
Expected timing of satisfaction period
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2023-01-01 | Appalachia
Performance obligations unsatisfied or partially unsatisfied
Expected timing of satisfaction period

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, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Net income (loss) attributable to ARLP	$ 27,199	$ 39,084	$ (164,248)	$ 373,582
Distributions to participating securities		$ (1,133)		(3,360)
Undistributed earnings attributable to participating securities	$ (581)			$ (2,655)
Weighted-average limited partner units outstanding - basic and diluted	127,195,219	128,391,191	127,154,398	128,311,609
Earnings per limited partner unit - basic and diluted	$ 0.21	$ 0.30	$ (1.29)	$ 2.86
Anti-dilutive under the treasury stock method (in units)	661,000	1,133,000	656,000	1,216,000
ARLP
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Net income (loss) attributable to ARLP	$ 27,199	$ 39,084	$ (164,248)	$ 373,582
Net income (loss) attributable to ARLP available to limited partners	$ 26,618	$ 37,951	$ (164,248)	$ 367,567

WORKERS' COMPENSATION AND PNE_3

WORKERS' COMPENSATION AND PNEUMOCONIOSIS - Workers' Compensation Liability (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019	Dec. 31, 2018
Reconciliation of changes in the workers' compensation liability
Beginning balance	$ 54,478	$ 53,425	$ 53,384	$ 49,539	$ 49,539
Accruals increase	1,599	2,395	3,539	6,603
Payments	(2,123)	(2,663)	(6,686)	(8,588)
Interest accretion	319	402	958	1,204
Valuation loss			3,078	4,801
Ending balance	54,273	$ 53,559	$ 54,273	$ 53,559	$ 53,384	$ 49,539
Workers' compensation discount rate			2.05%	3.06%	2.81%	3.89%
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, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Accrued Workers Compensation And Pneumoconiosis Benefits
Interest cost	$ 1,030	$ 1,217	$ 3,138	$ 3,649
Net amortization	969	980	3,096	2,941
Net periodic benefit cost	633	1,010	1,978	3,030
Pneumoconiosis benefits
Accrued Workers Compensation And Pneumoconiosis Benefits
Service cost	882	656	2,643	1,947
Interest cost	750	761	2,249	2,283
Net amortization	(172)	(1,145)	(515)	(3,436)
Net periodic benefit cost	$ 1,460	$ 272	$ 4,377	$ 794

COMPENSATION PLANS - LTIP Grant

COMPENSATION PLANS - LTIP Grants Activity (Details) - ARLP LTIP	9 Months Ended
	Sep. 30, 2020$ / sharesshares
Number of units
Balance at the beginning of the period (in units)	1,603,378
Granted (in units)	950,035
Vested (in units)	(424,486)
Forfeited (in units)	(13,835)
Balance at the end of the period (in units)	2,115,092
Weighted average grant date fair value per unit
Granted (in dollars per unit) | $ / shares	$ 9.62
Vested (in dollars per unit) | $ / shares	23.22
Forfeited (in dollars per unit) | $ / shares	$ 16.13
Other information
Common units issued upon vesting	279,622
Units not expected to vest (in units)	675,302

COMPENSATION PLANS - LTIP Other

COMPENSATION PLANS - LTIP Other Information (Details) - ARLP LTIP - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Jan. 01, 2020
Other information
Unit-based compensation expense	$ 1.6	$ 2.7	$ 2.5	$ 7.9
Reversal of cumulative previously recognized expenses			4.8
Total unit-based obligation recorded	11.3		$ 11.3
Units expected to vest (in units)			1,439,790
Units expected to vest (in dollars per units)			$ 13.33
Intrinsic value of unvested units	$ 4		$ 4
Intrinsic value of unvested per units	$ 2.77		$ 2.77
Unrecognized compensation expense (in dollars)	$ 7.9		$ 7.9
Weighted-average period for recognition of expense			1 year 7 months 6 days
Units available for grant	1,700,000		1,700,000		1,000,000

COMPENSATION PLANS - SERP and D

COMPENSATION PLANS - SERP and Directors Compensation Activity (Details) - SERP and Directors' Compensation Plans - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Other information
Unit-based compensation expense	$ 100	$ 400	$ 400	$ 1,100
Total unit-based obligation recorded	$ 16,300		$ 16,300
Phantom Share Units (PSUs)
Summary of units
Balance at the beginning of the period (in units)			631,365
Granted (in units)			29,544
Balance at the end of the period (in units)	660,909		660,909
Weighted average grant date fair value per unit
Balance at the beginning of the period (in dollars per unit)			$ 25.48
Granted (in dollars per unit)			7.87
Balance at the end of the period (in dollars per unit)	$ 24.69		$ 24.69
Intrinsic value (in dollars)
Intrinsic value of outstanding grants (in dollars)	$ 1,831		$ 1,831		$ 6,831

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, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Components of net periodic benefit cost:
Interest cost	$ 1,030	$ 1,217	$ 3,138	$ 3,649
Expected return on plan assets	(1,413)	(1,233)	(4,396)	(3,699)
Amortization of prior service cost	47	46	140	139
Amortization of net loss	969	980	3,096	2,941
Net periodic benefit cost	$ 633	$ 1,010	1,978	$ 3,030
2019 plan year
Components of net periodic benefit cost:
Employer contribution			$ 1,700

SEGMENT INFORMATION - General (

SEGMENT INFORMATION - General (Details)	9 Months Ended
	Sep. 30, 2020segment
SEGMENT INFORMATION
Number of reportable segments	3

SEGMENT INFORMATION - Segment R

SEGMENT INFORMATION - Segment Results (Details) $ in Thousands	Apr. 15, 2020employee	Sep. 30, 2020USD ($)	Sep. 30, 2019USD ($)	Sep. 30, 2020USD ($)	Sep. 30, 2019USD ($)	Dec. 31, 2019USD ($)
Reportable segment results
Revenues		$ 355,651	$ 464,726	$ 961,616	$ 1,508,382
Segment Adjusted EBITDA Expense		216,750	289,081	638,989	911,535
Segment Adjusted EBITDA		132,701	156,163	306,458	528,070
Total assets		2,231,340	2,627,089	2,231,340	2,627,089	$ 2,586,694
Capital expenditures		18,575	75,515	102,820	241,142
Gibson County mining complex
Segment Information
Number of employees terminated | employee	116
Hamilton mining complex
Segment Information
Number of employees terminated | employee	78
Illinois Basin
Reportable segment results
Revenues		210,360	280,335	552,019	965,404
Segment Adjusted EBITDA Expense		125,021	173,779	383,486	579,510
Segment Adjusted EBITDA		81,617	87,780	157,803	306,592
Total assets		1,082,992	1,418,008	1,082,992	1,418,008
Capital expenditures		3,815	49,829	44,073	157,759
Appalachia
Reportable segment results
Revenues		132,310	164,414	367,523	484,062
Segment Adjusted EBITDA Expense		86,447	107,990	240,116	312,861
Segment Adjusted EBITDA		43,358	55,178	121,416	167,612
Total assets		470,261	493,133	470,261	493,133
Capital expenditures		14,541	25,056	57,798	79,389
Minerals
Reportable segment results
Revenues		9,721	14,177	31,831	37,333
Segment Adjusted EBITDA Expense		849	2,517	2,851	6,109
Segment Adjusted EBITDA		8,898	12,202	29,534	32,432
Total assets		616,491	647,480	616,491	647,480
Other and Corporate
Reportable segment results
Revenues		6,070	13,123	18,409	43,275
Segment Adjusted EBITDA Expense		4,908	9,878	13,697	28,026
Segment Adjusted EBITDA		1,163	3,243	4,710	28,155
Total assets		468,590	561,171	468,590	561,171
Capital expenditures		219	630	949	3,994
Operating segments
Reportable segment results
Revenues		355,651	464,726	961,616	1,508,382
Operating segments | Illinois Basin
Reportable segment results
Revenues		210,360	276,042	552,019	952,941
Operating segments | Appalachia
Reportable segment results
Revenues		132,310	164,414	367,523	484,062
Operating segments | Minerals
Reportable segment results
Revenues		9,721	14,177	31,831	37,333
Operating segments | Other and Corporate
Reportable segment results
Revenues		3,260	10,093	10,243	34,046
Elimination
Reportable segment results
Revenues		(2,810)	(7,323)	(8,166)	(21,692)
Segment Adjusted EBITDA Expense		(475)	(5,083)	(1,161)	(14,971)
Segment Adjusted EBITDA		(2,335)	(2,240)	(7,005)	(6,721)
Total assets		(406,994)	(492,703)	(406,994)	(492,703)
Elimination | Illinois Basin
Reportable segment results
Revenues			4,293		12,463
Elimination | Other and Corporate
Reportable segment results
Revenues		$ 2,810	$ 3,030	$ 8,166	$ 9,229

SEGMENT INFORMATION - EBITDA Ex

SEGMENT INFORMATION - EBITDA Expense Reconciliation (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Reconciliation of consolidated Segment Adjusted EBITDA Expense to operating expenses (excluding depreciation, depletion and amortization)
Segment Adjusted EBITDA Expense	$ 216,750	$ 289,081	$ 638,989	$ 911,535
Outside coal purchases		(10,599)		(15,910)
Other expense	(723)	(228)	(1,456)	(370)
Operating expenses (excluding depreciation, depletion and amortization)	$ 216,027	$ 278,254	$ 637,533	$ 895,255

SEGMENT INFORMATION - EBITDA Re

SEGMENT INFORMATION - EBITDA Reconciliation (Details) - USD ($) $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2020	Sep. 30, 2019
Reconciliation of consolidated Segment Adjusted EBITDA to net income
Consolidated Segment Adjusted EBITDA	$ 132,701			$ 156,163			$ 306,458	$ 528,070
General and administrative	(13,871)			(17,885)			(41,131)	(55,218)
Depreciation, depletion and amortization	(80,182)			(72,348)			(237,662)	(220,400)
Asset impairment				(15,190)			(24,977)	(15,190)
Goodwill impairment							(132,026)
Interest expense, net	(11,156)			(11,606)			(34,799)	(33,510)
Acquisition gain								177,043
Income tax expense	(293)			(50)			(111)	(130)
Acquisition gain attributable to noncontrolling interest								(7,083)
NET INCOME (LOSS) ATTRIBUTABLE TO ARLP	27,199			39,084			(164,248)	373,582
Noncontrolling interest	36			117			97	7,407
NET INCOME (LOSS)	$ 27,235	$ (46,679)	$ (144,707)	$ 39,201	$ 58,184	$ 283,604	$ (164,151)	$ 380,989