Mineral properties and development costs - Additional information (Details) - USD ($) $ in Thousands			1 Months Ended		3 Months Ended			9 Months Ended		12 Months Ended		177 Months Ended
	Apr. 10, 2017	Jan. 11, 2010	Oct. 31, 2017	Oct. 19, 2011	Aug. 31, 2019	Feb. 28, 2019	Aug. 31, 2018	Aug. 31, 2019	Aug. 31, 2018	Nov. 30, 2018	Nov. 30, 2017	Aug. 31, 2019
Payments for mineral property								$ 31,000
Mineral properties expense					$ 10,951		$ 9,051	15,392	$ 12,657
Maximum Subscription Price	$ 150,000
Cost, Maintenance	10,000
Mineral properties funding (note 4 (c))								$ 10,200	$ 10,435
Payments to Acquire Projects	$ 5,000
Subscription of Options Description	To subscribe for 50% of the JV, South32 must contribute a minimum of $150 million, plus (i) any amounts Trilogy spends on matched parallel funding to a maximum of $16 million over the three year period and (ii) $5 million if the option had been exercised between April 1, 2018 and March 31, 2019 or $10 million if the option is exercised between April 1, 2019 and the expiration date of the option, less the amount of the initial funding contributed by South32
Approximationss [Member]
Payments for mineral property												$ 140,600
Acquisition costs												30,600
Mineral properties expense												$ 110,000
Titiribi Property [Member]
Mineral properties funding (note 4 (c))			$ 400			$ 10,200				$ 10,400	$ 10,000
Proceeds From Advances from Affiliates										$ 800
Regional Exploration Program Budget Funding						$ 1,000
Bornite Property [Member]
Payments for mineral property				$ 4,000
Net proceeds royalty				15.00%
Discount on consideration				$ 40,000
Bornite Property [Member] | Minimum [Member]
Mineral property interest percentage				16.00%
Net smelter return royalty				1.00%
Bornite Property [Member] | Maximum [Member]
Mineral property interest percentage				25.00%
Net smelter return royalty				2.50%
Ambler Property [Member]
Mineral property interest percentage		100.00%
Mineral property, fair value of consideration		$ 26,600
Net smelter return royalty		1.00%
Purchase price of the net smelter royalty		$ 10,000