Equity method investment - Financail information (Details) - USD ($) $ in Thousands	3 Months Ended				4 Months Ended	6 Months Ended
	May 31, 2020	Feb. 29, 2020	May 31, 2019	Feb. 28, 2019	May 31, 2020	May 31, 2020	May 31, 2019
Schedule of Equity Method Investments [Line Items]
Comprehensive loss	$ (3,002)	$ 171,179	$ (4,509)	$ (4,336)		$ 168,177	$ (8,845)
Summarizes on Equity Method Investment
Share of loss on equity investment for the six-month period ended May 31, 2020	(561)					(739)
May 31, 2020, equity method investment	175,261				$ 175,261	175,261
Summarized Financial Information, Income Statement
Amortization						58	75
General and administrative expense	433		$ 436			1,084	$ 928
Ambler Metals LLC
Schedule of Equity Method Investments [Line Items]
Comprehensive loss					1,480
Summarizes on Equity Method Investment
February 11, 2020, fair value ascribed to Ambler Metals LLC interest					176,000
Share of loss on equity investment for the six-month period ended May 31, 2020					(739)
May 31, 2020, equity method investment	175,261				175,261	175,261
Summarized Financial Information, Balance Sheet
Current assets: Cash, deposits and prepaid expenses	86,490				86,490	86,490
Non - current assets: Property, equipment and mineral properties	31,359				31,359	31,359
Loan receivable from South32	57,876				57,876	57,876
Current liabilities: Accounts payable and accrued liabilities	(917)				(917)	(917)
Non - current liabilities: Lease obligation	(79)				(79)	(79)
Net assets	$ 174,729				174,729	$ 174,729
Summarized Financial Information, Income Statement
Amortization					50
Mineral properties expense					1,080
General and administrative expense					904
Interest income					(557)
Comprehensive loss					$ 1,477