REVENUE - Disaggregation (Details) $ in Thousands	3 Months Ended		6 Months Ended
	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2018 USD ($) item	Dec. 31, 2017 USD ($)
Disaggregation of Revenue
Number of revenue sources | item			2
Royalty Revenue	$ 97,592	$ 114,348	$ 197,585	$ 226,824
Stream interest
Disaggregation of Revenue
Royalty Revenue	67,679	79,287	137,716	158,049
Stream interest | Mount Milligan
Disaggregation of Revenue
Royalty Revenue	28,169		37,015
Stream interest | Pueblo Viejo
Disaggregation of Revenue
Royalty Revenue	18,230		37,717
Stream interest | Wassa and Prestea
Disaggregation of Revenue
Royalty Revenue	9,550		17,611
Stream interest | Andacollo
Disaggregation of Revenue
Royalty Revenue	7,635		35,378
Stream interest | Other
Disaggregation of Revenue
Royalty Revenue	4,095		9,995
Stream interest | Gold
Disaggregation of Revenue
Royalty Revenue	53,179		112,293
Stream interest | Silver
Disaggregation of Revenue
Royalty Revenue	7,884		16,604
Stream interest | Copper
Disaggregation of Revenue
Royalty Revenue	6,616		8,819
Royalty interest
Disaggregation of Revenue
Royalty Revenue	29,913	$ 35,061	59,869	$ 68,775
Royalty interest | Penasquito
Disaggregation of Revenue
Royalty Revenue	4,660		8,297
Royalty interest | Cortez
Disaggregation of Revenue
Royalty Revenue	2,335		2,939
Royalty interest | Other
Disaggregation of Revenue
Royalty Revenue	22,918		48,633
Royalty interest | Gold
Disaggregation of Revenue
Royalty Revenue	19,656		38,210
Royalty interest | Silver
Disaggregation of Revenue
Royalty Revenue	1,567		2,919
Royalty interest | Copper
Disaggregation of Revenue
Royalty Revenue	4,359		7,974
Royalty interest | Other Metals
Disaggregation of Revenue
Royalty Revenue	$ 4,331		$ 10,766