SPECIAL PURPOSE ENTITIES (Details) $ in Millions	1 Months Ended	12 Months Ended
Oct. 31, 2018 USD ($)	Jan. 31, 2019 USD ($) item project
GPS
Variable Interest Entity
Number of natural gas-fired power plants \| project		2
Number of joint ventures \| item		2
Final cash distributions to joint ventures	$ 0.1
VIE
Variable Interest Entity
Development costs incurred		$ 1.9

The cash distribution made by the joint venture to the joint venture partner other then the reporting entity.

No definition available.

Name:	agx_JointVentureCashDistributionToJointVenturePartner
Namespace Prefix:	agx_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- 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

- 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

- Definition

Development costs incurred, including capitalized costs and costs charged to expense, in oil and gas activities.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 932
-SubTopic 235
-Section 50
-Paragraph 18
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=68064819&loc=d3e62014-109447

+ Details

Name:	us-gaap_CostsIncurredDevelopmentCosts
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- 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

- Details

Name:	dei_LegalEntityAxis=agx_GemmaPowerSystemsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis=us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: