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REVENUES FROM CONTRACTS WITH CUSTOMERS - Variable Consideration and Accounting for a Loss Contract (Details) - USD ($) $ in Millions | 12 Months Ended
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Jan. 31, 2020 | Jan. 31, 2019
Disaggregation of Revenue [Line Items] |  |
Amounts of unpriced change orders included in transaction prices | $ 20.6 | $ 18.8
Increase in cost of project | 33.6 |
Provision for contract loss | 5.8 |
Reversal of revenues previously recorded due to a change in the percentage of completion for the contract | 1.4 |
TeesREP Project [Member] |  |
Disaggregation of Revenue [Line Items] |  |
The total amounts of accounts receivable and contract assets with customer | $ 19.2 | $ 32.9

X
- Definition The total amounts of accounts receivable and contract assets related to the TeesREP project included in the consolidated balance sheets. + References No definition available. + Details
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Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- Definition The amount of cost of the project will exceed projected revenues . + References No definition available. + Details
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Namespace Prefix: | agx_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition The amount included in accrued expenses in the balance sheet (a current liability), representing a reserve for the excess of the costs expected to be incurred to complete the contract over the amount of revenues that will be recognized as the remaining work is completed. + References No definition available. + Details
Name: | agx_ProvisionForContractLoss
Namespace Prefix: | agx_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- Definition The amounts of unpriced change orders included in transaction prices that were used to determine revenues. + References No definition available. + Details
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Balance Type: | debit
Period Type: | instant

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- Definition Amount of increase (decrease) in revenue recognized for cumulative catch-up adjustment from change in measure of progress which (increases) decreases obligation to transfer good or service to customer for which consideration from customer has been received or is due. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 606 -SubTopic 10 -Section 50 -Paragraph 10 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=109196051&loc=SL49130551-203045 + Details
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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
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Namespace Prefix: | us-gaap_
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Balance Type: | na
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- Details
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Namespace Prefix: |
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Balance Type: |
Period Type: |