SEGMENT INFORMATION (Details) $ in Thousands	3 Months Ended		6 Months Ended
	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2019 USD ($) segment	Dec. 31, 2018 USD ($)	Jun. 30, 2019 USD ($)
Long Lived Assets and Pre-Tax Income by Geographical Information
Number of reportable segments | segment			2
Stream and royalty interests, net	$ 2,333,091		$ 2,333,091		$ 2,339,316
Revenue	123,643	$ 97,592	242,417	$ 197,585
Cost of sales	21,077	18,162	41,188	34,689
Production taxes	984	909	2,083	2,201
Depletion	39,982	38,759	78,643	81,264
Total segment gross profit	61,600	39,762	120,503	79,431
Canada
Long Lived Assets and Pre-Tax Income by Geographical Information
Stream and royalty interests, net	939,219		939,219		968,000
Dominican Republic
Long Lived Assets and Pre-Tax Income by Geographical Information
Stream and royalty interests, net	430,609		430,609		451,585
Chile
Long Lived Assets and Pre-Tax Income by Geographical Information
Stream and royalty interests, net	501,480		501,480		515,733
Africa
Long Lived Assets and Pre-Tax Income by Geographical Information
Stream and royalty interests, net	151,219		151,219		89,876
Mexico
Long Lived Assets and Pre-Tax Income by Geographical Information
Stream and royalty interests, net	79,891		79,891		83,748
United States
Long Lived Assets and Pre-Tax Income by Geographical Information
Stream and royalty interests, net	161,391		161,391		163,398
Australia
Long Lived Assets and Pre-Tax Income by Geographical Information
Stream and royalty interests, net	30,677		30,677		31,944
Rest of world
Long Lived Assets and Pre-Tax Income by Geographical Information
Stream and royalty interests, net	38,605		38,605		35,032
Stream interests
Long Lived Assets and Pre-Tax Income by Geographical Information
Stream and royalty interests, net	1,625,397		1,625,397		1,622,435
Revenue	89,625	67,679	176,606	137,716
Cost of sales	21,077	18,162	41,188	34,689
Depletion	32,181	28,636	63,643	60,733
Total segment gross profit	36,367	20,881	71,775	42,294
Stream interests | Canada
Long Lived Assets and Pre-Tax Income by Geographical Information
Stream and royalty interests, net	744,543		744,543		767,749
Revenue	38,191	32,264	75,854	47,010
Stream interests | Dominican Republic
Long Lived Assets and Pre-Tax Income by Geographical Information
Stream and royalty interests, net	430,609		430,609		451,585
Revenue	23,614	18,230	45,232	37,717
Stream interests | Chile
Long Lived Assets and Pre-Tax Income by Geographical Information
Stream and royalty interests, net	287,309		287,309		301,507
Revenue	20,665	7,635	41,269	35,378
Stream interests | Africa
Long Lived Assets and Pre-Tax Income by Geographical Information
Stream and royalty interests, net	150,898		150,898		89,555
Revenue	7,155	9,550	14,251	17,611
Stream interests | Rest of world
Long Lived Assets and Pre-Tax Income by Geographical Information
Stream and royalty interests, net	12,038		12,038		12,039
Royalty interests
Long Lived Assets and Pre-Tax Income by Geographical Information
Stream and royalty interests, net	707,694		707,694		716,881
Revenue	34,018	29,913	65,811	59,869
Production taxes	984	909	2,083	2,201
Depletion	7,801	10,123	15,000	20,531
Total segment gross profit	25,233	18,881	48,728	37,137
Royalty interests | Canada
Long Lived Assets and Pre-Tax Income by Geographical Information
Stream and royalty interests, net	194,676		194,676		200,251
Revenue	8,037	7,536	16,958	17,717
Royalty interests | Chile
Long Lived Assets and Pre-Tax Income by Geographical Information
Stream and royalty interests, net	214,171		214,171		214,226
Royalty interests | Africa
Long Lived Assets and Pre-Tax Income by Geographical Information
Stream and royalty interests, net	321		321		321
Revenue	911	532	1,606	1,024
Royalty interests | Mexico
Long Lived Assets and Pre-Tax Income by Geographical Information
Stream and royalty interests, net	79,891		79,891		83,748
Revenue	9,376	7,837	15,763	15,833
Royalty interests | United States
Long Lived Assets and Pre-Tax Income by Geographical Information
Stream and royalty interests, net	161,391		161,391		163,398
Revenue	10,012	8,284	20,614	14,340
Royalty interests | Australia
Long Lived Assets and Pre-Tax Income by Geographical Information
Stream and royalty interests, net	30,677		30,677		31,944
Revenue	3,546	3,157	7,348	6,217
Royalty interests | Rest of world
Long Lived Assets and Pre-Tax Income by Geographical Information
Stream and royalty interests, net	26,567		26,567		$ 22,993
Revenue	$ 2,136	$ 2,567	$ 3,522	$ 4,738