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Legal Contingencies - Additional Information (Detail) (USD $)
In Millions, unless otherwise specified
 1 Months Ended
Apr. 30, 2015
Mar. 31, 2008
Jan. 31, 2015
Loss Contingencies [Line Items]      
Payment received from proceeds deposited with bankruptcy court $ 1.6agx_BankruptcyClaimsAmountReceivedFromAmountOfClaimsRetainedByCourt    
GPS [Member]      
Loss Contingencies [Line Items]      
Net proceeds held by the bankruptcy court     5.5agx_BankruptcyClaimsAmountOfClaimsRetainedByCourt
/ dei_LegalEntityAxis
= agx_GemmaPowerSystemsMember
GPS [Member] | Procurement and Construction Services Related to Nebraska Project [Member]      
Loss Contingencies [Line Items]      
GPS mechanics lien against Nebraska project   $ 23.8us-gaap_BankruptcyClaimsAmountOfClaimsFiled
/ dei_LegalEntityAxis
= agx_GemmaPowerSystemsMember
/ us-gaap_LitigationCaseAxis
= agx_ProcurementAndConstructionServicesRelatedToNebraskaProjectMember