Warranty Liability (Narrative) (Details)	12 Months Ended
Mar. 31, 2020
Warranty Provision Abstract
Warranty provision as a percentage of revenue from product sales	3.50%

Represents warranty provision as a percentage of revenue from product sales.

No definition available.

Name:	gpvrf_WarrantyProvisionAsPercentageOfRevenueFromProductSales
Namespace Prefix:	gpvrf_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration