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INCOME TAXES - Income Tax Returns (Details) - USD ($) $ in Millions | 9 Months Ended | 12 Months Ended
--- | --- | ---
Oct. 31, 2019 | Jan. 31, 2019
INCOME TAXES |  |
Prepaid income taxes and income taxes receivable | $ 14.9 | $ 19.5

X
- Definition Represents the total amount of prepaid income taxes and income taxes receivable. + References No definition available. + Details
Name: | agx_PrepaidIncomeTaxesAndIncomeTaxesReceivable
Namespace Prefix: | agx_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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