REVENUES FROM CONTRACT WITH CUSTOMERS (Details) - USD ($) $ in Millions	Jul. 31, 2020	Jan. 31, 2020
REVENUES FROM CONTRACT WITH CUSTOMERS
Retained amounts by project owners	$ 27.2	$ 20.0
Amounts of unpriced change orders included in transaction prices	8.9	20.6

The amounts retained by project owners under construction contracts.

No definition available.

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