ACQUISITIONS AND DISPOSITIONS - Peak Gold (Details) - USD ($) $ in Thousands			3 Months Ended	12 Months Ended
	Sep. 30, 2020	Sep. 29, 2020	Sep. 30, 2020	Jun. 30, 2021	Mar. 31, 2021	Jun. 30, 2020
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proceeds from sale of Peak Gold JV interest				$ 49,154
Proceeds from sale of Contango shares				12,146
Stream and royalty interest				2,262,158		$ 2,318,913
Gain on sale of Peak Gold JV interest				33,906
Peak Gold LLC
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Total cash consideration	$ 4,000
Percentage of royalty that can be acquired	50.00%
Peak Gold/Manh Choh
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Net smelter return (NSR) (as a percent)	28.00%
Stream and royalty interest					$ 4,400
Alaska mining claims
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Net smelter return (NSR) (as a percent)	3.00%	2.00%
Percentage of royalty that can be acquired	1.00%
Peak Gold/Manh Choh
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Percentage of ownership interest	40.00%		40.00%			40.00%
Proceeds from sale of Peak Gold JV interest	$ 49,200
Total cash consideration	$ 61,300
Gain on sale of Peak Gold JV interest			$ 33,900
Contango
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of shares sold	809,744		809,744
Proceeds from sale of Contango shares	$ 12,100
Mark-to-market increase on sale			$ 3,600	$ 3,600