SEGMENT INFORMATION (Details) $ in Thousands	3 Months Ended								12 Months Ended
	Jun. 30, 2019 USD ($)	Mar. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Sep. 30, 2018 USD ($)	Jun. 30, 2018 USD ($)	Mar. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Sep. 30, 2017 USD ($)	Jun. 30, 2019 USD ($) segment	Jun. 30, 2018 USD ($)	Jun. 30, 2017 USD ($)
Long Lived Assets and Pre-Tax Income by Geographical Information
Number of reportable segments | segment									2
Cost	$ 3,397,998				$ 3,636,306				$ 3,397,998	$ 3,636,306
Impairments					(239,364)					(239,364)
Stream and royalty interests, net (Note 4)	2,339,316				2,501,117				2,339,316	2,501,117
Revenue	115,694	$ 109,778	$ 97,592	$ 99,992	116,235	$ 115,983	$ 114,348	$ 112,476	423,056	459,042	$ 440,814
Cost of sales									77,535	83,839	87,265
Production taxes									4,112	2,268	1,760
Depletion									162,856	163,586	159,553
Total segment gross profit									178,553	209,349	192,236
Canada
Long Lived Assets and Pre-Tax Income by Geographical Information
Impairments					(284)					(284)
Stream and royalty interests, net (Note 4)	968,000				1,023,778				968,000	1,023,778
Dominican Republic
Long Lived Assets and Pre-Tax Income by Geographical Information
Stream and royalty interests, net (Note 4)	451,585				495,460				451,585	495,460
Chile
Long Lived Assets and Pre-Tax Income by Geographical Information
Impairments					(239,080)					(239,080)
Stream and royalty interests, net (Note 4)	515,733				542,557				515,733	542,557
Africa
Long Lived Assets and Pre-Tax Income by Geographical Information
Stream and royalty interests, net (Note 4)	89,876				105,376				89,876	105,376
Mexico
Long Lived Assets and Pre-Tax Income by Geographical Information
Stream and royalty interests, net (Note 4)	83,748				93,277				83,748	93,277
United States
Long Lived Assets and Pre-Tax Income by Geographical Information
Stream and royalty interests, net (Note 4)	163,398				165,543				163,398	165,543
Australia
Long Lived Assets and Pre-Tax Income by Geographical Information
Stream and royalty interests, net (Note 4)	31,944				34,254				31,944	34,254
Other
Long Lived Assets and Pre-Tax Income by Geographical Information
Stream and royalty interests, net (Note 4)	35,032				40,872				35,032	40,872
Stream interests
Long Lived Assets and Pre-Tax Income by Geographical Information
Cost	1,622,435				1,750,204				1,622,435	1,750,204
Revenue									305,824	324,516	314,011
Cost of sales									77,535	83,839	87,265
Depletion									127,770	129,662	121,530
Total segment gross profit									100,519	111,015	105,216
Stream interests | Canada
Long Lived Assets and Pre-Tax Income by Geographical Information
Cost	767,749				809,500				767,749	809,500
Revenue									123,152	142,244	136,736
Stream interests | Dominican Republic
Long Lived Assets and Pre-Tax Income by Geographical Information
Cost	451,585				495,460				451,585	495,460
Revenue									82,844	95,055	91,589
Stream interests | Chile
Long Lived Assets and Pre-Tax Income by Geographical Information
Cost	301,507				328,331				301,507	328,331
Revenue									69,264	57,413	60,251
Stream interests | Africa
Long Lived Assets and Pre-Tax Income by Geographical Information
Cost	89,555				104,874				89,555	104,874
Revenue									30,564	29,804	25,435
Stream interests | Other
Long Lived Assets and Pre-Tax Income by Geographical Information
Cost	12,039				12,039				12,039	12,039
Royalty interests
Long Lived Assets and Pre-Tax Income by Geographical Information
Cost	716,881				990,277				716,881	990,277
Revenue									117,232	134,526	126,803
Production taxes									4,112	2,268	1,760
Depletion									35,086	33,924	38,023
Total segment gross profit									78,034	98,334	87,020
Royalty interests | Canada
Long Lived Assets and Pre-Tax Income by Geographical Information
Cost	200,251				214,562				200,251	214,562
Revenue									32,602	24,254	23,208
Royalty interests | Chile
Long Lived Assets and Pre-Tax Income by Geographical Information
Cost	214,226				453,306				214,226	453,306
Revenue										473	1,648
Royalty interests | Africa
Long Lived Assets and Pre-Tax Income by Geographical Information
Cost	321				502				321	502
Revenue									1,416	2,098	3,131
Royalty interests | Mexico
Long Lived Assets and Pre-Tax Income by Geographical Information
Cost	83,748				93,277				83,748	93,277
Revenue									27,224	42,959	41,945
Royalty interests | United States
Long Lived Assets and Pre-Tax Income by Geographical Information
Cost	163,398				165,543				163,398	165,543
Revenue									34,845	39,496	35,282
Royalty interests | Australia
Long Lived Assets and Pre-Tax Income by Geographical Information
Cost	31,944				34,254				31,944	34,254
Revenue									12,806	13,710	12,943
Royalty interests | Other
Long Lived Assets and Pre-Tax Income by Geographical Information
Cost	$ 22,993				$ 28,833				22,993	28,833
Revenue									$ 8,339	$ 11,536	$ 8,646