DESCRIPTION OF THE BUSINESS AND BASIS OF PRESENTATION (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
Apr. 30, 2021	Jan. 31, 2021
DESCRIPTION OF THE BUSINESS AND BASIS OF PRESENTATION
Cost of property, plant and equipment	$ 7.7	$ 7.5

Amount of costs incurred related to activities to develop a gas-fired power plant to get a fixed asset ready for operation.

No definition available.

Name:	agx_CostIncurredRelatedToActivitiesToDevelopGasFiredPowerPlant
Namespace Prefix:	agx_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration