SEGMENT INFORMATION (Details) $ in Thousands	3 Months Ended								12 Months Ended
	Jun. 30, 2020 USD ($)	Mar. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Sep. 30, 2019 USD ($)	Jun. 30, 2019 USD ($)	Mar. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Sep. 30, 2018 USD ($)	Jun. 30, 2020 USD ($) segment	Jun. 30, 2019 USD ($)	Jun. 30, 2018 USD ($)
Long Lived Assets and Pre-Tax Income by Geographical Information
Number of reportable segments | segment									2
Stream and royalty interests, net	$ 2,318,913				$ 2,339,316				$ 2,318,913	$ 2,339,316
Revenue (Note 7)	119,965	$ 136,437	$ 123,643	$ 118,774	115,694	$ 109,778	$ 97,592	$ 99,992	498,819	423,056	$ 459,042
Cost of sales									83,890	77,535	83,839
Production taxes									3,824	4,112	2,268
Depletion									175,047	162,856	163,586
Total segment gross profit									236,058	178,553	209,349
Canada
Long Lived Assets and Pre-Tax Income by Geographical Information
Stream and royalty interests, net	892,587				968,000				892,587	968,000
Dominican Republic
Long Lived Assets and Pre-Tax Income by Geographical Information
Stream and royalty interests, net	406,469				451,585				406,469	451,585
Chile
Long Lived Assets and Pre-Tax Income by Geographical Information
Stream and royalty interests, net	501,583				515,733				501,583	515,733
Africa
Long Lived Assets and Pre-Tax Income by Geographical Information
Stream and royalty interests, net	215,784				89,877				215,784	89,877
Mexico
Long Lived Assets and Pre-Tax Income by Geographical Information
Stream and royalty interests, net	75,951				83,748				75,951	83,748
United States
Long Lived Assets and Pre-Tax Income by Geographical Information
Stream and royalty interests, net	159,445				163,398				159,445	163,398
Australia
Long Lived Assets and Pre-Tax Income by Geographical Information
Stream and royalty interests, net	30,006				31,944				30,006	31,944
Rest of world
Long Lived Assets and Pre-Tax Income by Geographical Information
Stream and royalty interests, net	37,088				35,031				37,088	35,031
Stream interests
Long Lived Assets and Pre-Tax Income by Geographical Information
Stream and royalty interests, net	1,614,363				1,622,435				1,614,363	1,622,435
Revenue (Note 7)									359,868	305,824	324,516
Cost of sales									83,890	77,535	83,839
Depletion									144,678	127,770	129,662
Total segment gross profit									131,300	100,519	111,015
Stream interests | Canada
Long Lived Assets and Pre-Tax Income by Geographical Information
Stream and royalty interests, net	702,732				767,749				702,732	767,749
Revenue (Note 7)									158,736	123,152	142,244
Stream interests | Dominican Republic
Long Lived Assets and Pre-Tax Income by Geographical Information
Stream and royalty interests, net	406,469				451,585				406,469	451,585
Revenue (Note 7)									96,978	82,844	95,055
Stream interests | Chile
Long Lived Assets and Pre-Tax Income by Geographical Information
Stream and royalty interests, net	277,661				301,507				277,661	301,507
Revenue (Note 7)									74,219	69,264	57,413
Stream interests | Africa
Long Lived Assets and Pre-Tax Income by Geographical Information
Stream and royalty interests, net	215,463				89,556				215,463	89,556
Revenue (Note 7)									29,935	30,564	29,804
Stream interests | Rest of world
Long Lived Assets and Pre-Tax Income by Geographical Information
Stream and royalty interests, net	12,038				12,038				12,038	12,038
Royalty interests
Long Lived Assets and Pre-Tax Income by Geographical Information
Stream and royalty interests, net	704,550				716,881				704,550	716,881
Revenue (Note 7)									138,951	117,232	134,526
Production taxes									3,824	4,112	2,268
Depletion									30,369	35,086	33,924
Total segment gross profit									104,758	78,034	98,334
Royalty interests | Canada
Long Lived Assets and Pre-Tax Income by Geographical Information
Stream and royalty interests, net	189,855				200,251				189,855	200,251
Revenue (Note 7)									30,524	32,602	24,254
Royalty interests | Chile
Long Lived Assets and Pre-Tax Income by Geographical Information
Stream and royalty interests, net	223,922				214,226				223,922	214,226
Revenue (Note 7)											473
Royalty interests | Africa
Long Lived Assets and Pre-Tax Income by Geographical Information
Stream and royalty interests, net	321				321				321	321
Revenue (Note 7)									2,575	1,416	2,098
Royalty interests | Mexico
Long Lived Assets and Pre-Tax Income by Geographical Information
Stream and royalty interests, net	75,951				83,748				75,951	83,748
Revenue (Note 7)									32,731	27,224	42,959
Royalty interests | United States
Long Lived Assets and Pre-Tax Income by Geographical Information
Stream and royalty interests, net	159,445				163,398				159,445	163,398
Revenue (Note 7)									48,692	34,845	39,496
Royalty interests | Australia
Long Lived Assets and Pre-Tax Income by Geographical Information
Stream and royalty interests, net	30,006				31,944				30,006	31,944
Revenue (Note 7)									15,252	12,806	13,710
Royalty interests | Rest of world
Long Lived Assets and Pre-Tax Income by Geographical Information
Stream and royalty interests, net	$ 25,050				$ 22,993				25,050	22,993
Revenue (Note 7)									$ 9,177	$ 8,339	$ 11,536