REVENUE - Property Disaggregation (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2020	Mar. 31, 2019
Disaggregation of Revenue
Revenue	$ 136,437	$ 109,778	$ 378,853	$ 307,362
Stream interests
Disaggregation of Revenue
Revenue	97,460	77,765	274,065	215,480
Stream interests | Mount Milligan
Disaggregation of Revenue
Revenue	32,298	26,938	93,423	63,954
Stream interests | Pueblo Viejo
Disaggregation of Revenue
Revenue	28,302	20,787	73,534	58,504
Stream interests | Andacollo
Disaggregation of Revenue
Revenue	22,055	15,638	63,324	51,016
Stream interests | Wassa and Prestea
Disaggregation of Revenue
Revenue	8,647	5,773	18,760	17,557
Stream interests | Rainy River
Disaggregation of Revenue
Revenue	4,838	7,074	19,566	17,067
Stream interests | Other
Disaggregation of Revenue
Revenue	1,320	1,555	5,458	7,382
Royalty interests
Disaggregation of Revenue
Revenue	38,977	32,013	104,788	91,882
Royalty interests | Other
Disaggregation of Revenue
Revenue	25,152	23,421	71,257	72,053
Royalty interests | Penasquito
Disaggregation of Revenue
Revenue	7,425	4,465	19,422	12,763
Royalty interests | Cortez
Disaggregation of Revenue
Revenue	$ 6,400	$ 4,127	$ 14,109	$ 7,066