REVENUE - Property 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 | Mount Milligan
Disaggregation of Revenue
Revenue (Note 7)									131,425	101,010
Stream interests | Pueblo Viejo
Disaggregation of Revenue
Revenue (Note 7)									96,978	82,844
Stream interests | Andacollo
Disaggregation of Revenue
Revenue (Note 7)									74,219	69,264
Stream interests | Wassa
Disaggregation of Revenue
Revenue (Note 7)									23,203	22,098
Stream interests | Other
Disaggregation of Revenue
Revenue (Note 7)									34,043	30,608
Royalty interests
Disaggregation of Revenue
Revenue (Note 7)									138,951	117,232	$ 134,526
Royalty interests | Other
Disaggregation of Revenue
Revenue (Note 7)									91,111	91,984
Royalty interests | Penasquito
Disaggregation of Revenue
Revenue (Note 7)									25,498	13,865
Royalty interests | Cortez
Disaggregation of Revenue
Revenue (Note 7)									$ 22,342	$ 11,383