REVENUE - Disaggregation (Details) $ in Thousands	3 Months Ended		9 Months Ended
	Mar. 31, 2019 USD ($)	Mar. 31, 2018 USD ($)	Mar. 31, 2019 USD ($) item	Mar. 31, 2018 USD ($)
Disaggregation of Revenue
Number of revenue sources | item			2
Royalty Revenue	$ 109,778	$ 115,983	$ 307,362	$ 342,807
Stream interest
Disaggregation of Revenue
Royalty Revenue	77,765	82,979	215,480	241,028
Stream interest | Mount Milligan
Disaggregation of Revenue
Royalty Revenue	26,938		63,954
Stream interest | Pueblo Viejo
Disaggregation of Revenue
Royalty Revenue	20,787		58,504
Stream interest | Andacollo
Disaggregation of Revenue
Royalty Revenue	15,638		51,016
Stream interest | Wassa and Prestea
Disaggregation of Revenue
Royalty Revenue	7,328		24,939
Stream interest | Other
Disaggregation of Revenue
Royalty Revenue	7,074		17,067
Stream interest | Gold
Disaggregation of Revenue
Royalty Revenue	62,856		175,149
Stream interest | Silver
Disaggregation of Revenue
Royalty Revenue	7,908		24,512
Stream interest | Copper
Disaggregation of Revenue
Royalty Revenue	7,001		15,819
Royalty interest
Disaggregation of Revenue
Royalty Revenue	32,013	$ 33,004	91,882	$ 101,779
Royalty interest | Penasquito
Disaggregation of Revenue
Royalty Revenue	4,465		12,763
Royalty interest | Cortez
Disaggregation of Revenue
Royalty Revenue	4,127		7,066
Royalty interest | Other
Disaggregation of Revenue
Royalty Revenue	23,421		72,053
Royalty interest | Gold
Disaggregation of Revenue
Royalty Revenue	22,041		60,251
Royalty interest | Silver
Disaggregation of Revenue
Royalty Revenue	1,608		4,527
Royalty interest | Copper
Disaggregation of Revenue
Royalty Revenue	3,056		11,030
Royalty interest | Other Metals
Disaggregation of Revenue
Royalty Revenue	$ 5,308		$ 16,074