REVENUE - Metal Disaggregation (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2018
Disaggregation of Revenue
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
Stream interests
Disaggregation of Revenue
Revenue (Note 7)									359,868	305,824	324,516
Stream interests | Gold
Disaggregation of Revenue
Revenue (Note 7)									294,490	249,496
Stream interests | Silver
Disaggregation of Revenue
Revenue (Note 7)									32,744	33,282
Stream interests | Copper
Disaggregation of Revenue
Revenue (Note 7)									32,634	23,046
Royalty interests
Disaggregation of Revenue
Revenue (Note 7)									138,951	117,232	$ 134,526
Royalty interests | Gold
Disaggregation of Revenue
Revenue (Note 7)									98,153	78,570
Royalty interests | Silver
Disaggregation of Revenue
Revenue (Note 7)									9,996	5,497
Royalty interests | Copper
Disaggregation of Revenue
Revenue (Note 7)									13,528	13,808
Royalty interests | Other
Disaggregation of Revenue
Revenue (Note 7)									$ 17,274	$ 19,357