REVENUE - Property Disaggregation (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2019	Dec. 31, 2018
Disaggregation of Revenue
Revenue	$ 123,643	$ 97,592	$ 242,417	$ 197,585
Stream interests
Disaggregation of Revenue
Revenue	89,625	67,679	176,606	137,716
Stream interests | Mount Milligan
Disaggregation of Revenue
Revenue	30,629	28,169	61,126	37,015
Stream interests | Pueblo Viejo
Disaggregation of Revenue
Revenue	23,614	18,230	45,232	37,717
Stream interests | Andacollo
Disaggregation of Revenue
Revenue	20,665	7,635	41,269	35,378
Stream interests | Wassa and Prestea
Disaggregation of Revenue
Revenue	4,794	6,459	10,113	11,784
Stream interests | Rainy River
Disaggregation of Revenue
Revenue	7,562	4,095	14,728	9,995
Stream interests | Other
Disaggregation of Revenue
Revenue	2,361	3,091	4,138	5,827
Royalty interests
Disaggregation of Revenue
Revenue	34,018	29,913	65,811	59,869
Royalty interests | Other
Disaggregation of Revenue
Revenue	23,149	22,918	46,105	48,633
Royalty interests | Penasquito
Disaggregation of Revenue
Revenue	7,577	4,660	11,997	8,297
Royalty interests | Cortez
Disaggregation of Revenue
Revenue	$ 3,292	$ 2,335	$ 7,709	$ 2,939