Accounts receivable - Additional information (Details) $ in Thousands	Feb. 29, 2020 USD ($)
Accounts receivable
Service agreement cost	$ 110
Staking cost	120
invoices paid on behalf of Ambler Metals LLC	$ 130

Amounts due from an entity in which the reporting entity shares joint control with another party or group, due within 1 year (or 1 business cycle).

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Name:	us-gaap_DueFromJointVenturesCurrent
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant