ACCOUNTS AND NOTES RECEIVABLE (Details) - USD ($) $ in Millions	Apr. 30, 2019	Jan. 31, 2019
ACCOUNTS AND NOTES RECEIVABLE
Outstanding balances of accounts receivable and contract assets	$ 19.6	$ 17.1

Amount of outstanding balances which includes accounts receivable and contract assets.

No definition available.

Name:	agx_InvoicesOutstandingBalanceIncludedInAccountsReceivableAndContractAssets
Namespace Prefix:	agx_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant