XML 67 R56.htm IDEA: XBRL DOCUMENT
v3.26.1

Commitments and Contingencies - Restricted Investments (Details) - USD ($) $ in Thousands | Jun. 30, 2026 | Dec. 31, 2025
--- | --- | ---
Long-term Purchase Commitment [Line Items] |  |
Total long-term restricted investments | $ 34,453 | $ 34,356
Workers’ compensation obligations |  |
Long-term Purchase Commitment [Line Items] |  |
Total long-term restricted investments | 3,168 | 3,172
Reclamation-related obligations |  |
Long-term Purchase Commitment [Line Items] |  |
Total long-term restricted investments | 27,268 | 27,238
Financial payments and other performance obligations |  |
Long-term Purchase Commitment [Line Items] |  |
Total long-term restricted investments | $ 4,017 | $ 3,946

X
- 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_LongTermPurchaseCommitmentLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Investments which are not defined as or included in marketable (debt, equity, or other) securities whose use is restricted in whole or in part, generally by contractual agreements or regulatory requirements. For use in an unclassified balance sheet. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 954 -SubTopic 210 -Name Accounting Standards Codification -Section 45 -Paragraph 4 -Publisher FASB -URI https://asc.fasb.org/1943274/2147477220/954-210-45-4 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 954 -SubTopic 210 -Name Accounting Standards Codification -Section 50 -Paragraph 2 -Publisher FASB -URI https://asc.fasb.org/1943274/2147478600/954-210-50-2 + Details
Name: | us-gaap_RestrictedInvestments
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Details
Name: | us-gaap_CollateralAxis=amr_WorkersCompensationObligationsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_CollateralAxis=amr_ReclamationRelatedObligationsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_CollateralAxis=amr_FinancialPaymentsAndOtherPerformanceObligationsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |