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Inventories - Narrative (Details) - USD ($) | 9 Months Ended | 12 Months Ended
--- | --- | ---
Jun. 30, 2020 | Sep. 30, 2019
Inventory Disclosure [Abstract] |  |
Proceeds received from insurance relating to property and casualty damage claims |  | $ 486,000
Proceeds from federal relief grants | $ 4,629,000 | $ 15,597,000

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- Definition Proceeds From Federal Relief Grants + References No definition available. + Details
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Namespace Prefix: | alco_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- Definition Proceeds Received from Insurance Relating to Property and Casualty Damage Claims + References No definition available. + Details
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Namespace Prefix: | alco_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- References No definition available. + Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration