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VARIABLE INTEREST ENTITIES - WKY CoalPlay (Details) - USD ($) $ in Thousands | 12 Months Ended
--- | ---
Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018
Coal lease |  |  |
Variable Interest Entities |  |  |
Payments | $ 13,819 | $ 15,317 | $ 10,818

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- Definition Amount paid during the period for minimum royalty obligations. + References No definition available. + Details
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Namespace Prefix: | arlp_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
Name: | us-gaap_VariableInterestEntityLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Details
Name: | us-gaap_RelatedPartyTransactionAxis=arlp_CoalLeaseMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |