Amount of potential cash payment that could result from the contingent consideration arrangement.

No definition available.

Name:	agx_BusinessAcquisitionContingentConsiderationPotentialCashPayments
Namespace Prefix:	agx_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Business acquisitions pro forma profit loss.

+ References

No definition available.

+ Details

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

- Definition

Represents the amount of cash paid in connection with acquisition related to retirement of debt and certain leases.

+ References

No definition available.

+ Details

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

- Definition

Represents the ownership interest held.

+ References

No definition available.

+ Details

Name:	agx_OwnershipInterestOwned
Namespace Prefix:	agx_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

The cash portion associated with the acquisition of business during the period before cash acquired.

+ References

No definition available.

+ Details

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

- Definition

Percentage of development success fee that was paid to equipment seller.

+ References

No definition available.

+ Details

Name:	agx_PercentageOfDevelopmentSuccessFeePaidToEquipmentSeller
Namespace Prefix:	agx_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Percentage of development success fee that was received.

+ References

No definition available.

+ Details

Name:	agx_PercentageOfDevelopmentSuccessFeeReceivedUponSale
Namespace Prefix:	agx_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

The pro forma basic net income per share for a period as if the business combination or combinations had been completed at the beginning of a period.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (h)(2)-(3)
-URI http://asc.fasb.org/extlink&oid=56956515&loc=d3e1392-128463

+ Details

Name:	us-gaap_BusinessAcquisitionProFormaEarningsPerShareBasic
Namespace Prefix:	us-gaap_
Data Type:	num:perShareItemType
Balance Type:	na
Period Type:	duration

- Definition

The pro forma diluted net income per share for a period as if the business combination or combinations had been completed at the beginning of a period.

+ References

+ Details

Name:	us-gaap_BusinessAcquisitionProFormaEarningsPerShareDiluted
Namespace Prefix:	us-gaap_
Data Type:	num:perShareItemType
Balance Type:	na
Period Type:	duration

- References

No definition available.

+ Details

Name:	us-gaap_BusinessAcquisitionProFormaInformationAbstract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

The pro forma net Income or Loss for the period as if the business combination or combinations had been completed at the beginning of a period.

+ References

+ Details

Name:	us-gaap_BusinessAcquisitionsProFormaNetIncomeLoss
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

The pro forma revenue for a period as if the business combination or combinations had been completed at the beginning of the period.

+ References

+ Details

Name:	us-gaap_BusinessAcquisitionsProFormaRevenue
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- References

No definition available.

+ Details

Name:	us-gaap_EarningsPerShareProFormaAbstract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

The cash inflow associated with the amount received from the sale of a portion of the company's business, for example a segment, division, branch or other business, during the period.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 12
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=56944662&loc=d3e3179-108585

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Investing Activities
-URI http://asc.fasb.org/extlink&oid=6516133

+ Details

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

- Definition

Detail information of subsequent event by type. User is expected to use existing line items from elsewhere in the taxonomy as the primary line items for this disclosure, which is further associated with dimension and member elements pertaining to a subsequent event.

+ References

No definition available.

+ Details

Name:	us-gaap_SubsequentEventLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_BusinessAcquisitionAxis=agx_RobertsCompanyAndAtlanticProjectsCompanyLimitedMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_SubsequentEventTypeAxis=us-gaap_SubsequentEventMember
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:

- Details

Name:	us-gaap_BusinessAcquisitionAxis=agx_RobertsCompanyMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

SUBSEQUENT EVENTS (Details) - USD ($)		1 Months Ended	9 Months Ended
SUBSEQUENT EVENTS (Details) - USD ($)	Dec. 04, 2015	Nov. 30, 2015	Oct. 31, 2015	Oct. 31, 2014
Roberts Company And Atlantic Projects Company Limited Member
Business Acquisition, Pro Forma Information [Abstract]
Pro forma revenues			$ 452,474,000	$ 379,869,000
Pro forma net income			31,763,000	34,456,000
Pro forma net income attributable to the stockholders of Argan, Inc.			$ 20,336,000	$ 25,323,000
Earnings Per Share, Pro Forma [Abstract]
Basic (in dollars per share)			$ 1.38	$ 1.75
Diluted (in dollars per share)			$ 1.35	$ 1.72
Subsequent Event [Member] \| Variable Interest Entity [Member]
Subsequent Event [Line Items]
Proceeds from sale of business		$ 2,555,000
Percentage of development success fee received		60.00%
Percentage of development success fee paid to Moxie Freedom's equipment supplier		40.00%
Subsequent Event [Member] \| The Roberts Company Member
Subsequent Event [Line Items]
Cash paid at closing	$ 500,000
Potential additional cash payments for achievement of performance conditions	500,000
Cash payments to retire outstanding debt and certain leases	$ 16,000,000
Subsequent Event [Member] \| The Roberts Company Member \| TRC Acquisition LLC Member
Subsequent Event [Line Items]
Ownership interest (as a percent)	100.00%