Mineral properties and development costs - Mineral property expenses (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Aug. 31, 2019	Aug. 31, 2018	Aug. 31, 2019	Aug. 31, 2018
Mineral property expense	$ 10,951	$ 9,051	$ 15,392	$ 12,657
Alaska, USA [Member]
Community	164	81	428	324
Drilling	4,760	3,624	4,933	3,804
Engineering	663	245	1,287	750
Environmental	153	313	424	482
Geochemistry and geophysics	252	420	1,010	1,066
Land and permitting	163	145	523	504
Project support	3,062	2,703	4,066	3,381
Other income			(1)	(20)
Wages and benefits	$ 1,734	$ 1,520	$ 2,722	$ 2,366