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SPECIAL PURPOSE ENTITIES - Additional Information (Details) - GPS | 12 Months Ended
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Jan. 31, 2018 item project
Variable Interest Entity |
Number of natural gas-fired power plants | project | 2
Number of joint ventures | item | 2

X
- Definition Represents the number of natural gas-fired power plants for which the entity has assigned its contracts for engineering, procurement and construction. + References No definition available. + Details
Name: | agx_NaturalGasFiredPowerPlantsAssignedContractsNumber
Namespace Prefix: | agx_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | duration

X
- Definition Number of joint venture under contract with company. + References No definition available. + Details
Name: | agx_NumberOfJointVentureUnderContractWithCompany
Namespace Prefix: | agx_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | instant

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

X
- Details
Name: | dei_LegalEntityAxis=agx_GemmaPowerSystemsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |