SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES AND RECENTLY ISSUED AND RECENTLY ADOPTED ACCOUNTING PRONOUNCEMENTS - SEGMENTS (Details) $ in Thousands	3 Months Ended								12 Months Ended
	Jun. 30, 2017 USD ($)	Mar. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Sep. 30, 2016 USD ($)	Jun. 30, 2016 USD ($)	Mar. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Sep. 30, 2015 USD ($)	Jun. 30, 2017 USD ($) segment	Jun. 30, 2016 USD ($)	Jun. 30, 2015 USD ($)
Long Lived Assets and Pre-Tax Income by Geographical Information
Number of reportable segments | segment									2
Stream and royalty interests, net	$ 2,892,256				$ 2,848,087				$ 2,892,256	$ 2,848,087
Revenue	108,934	$ 106,972	$ 106,961	$ 117,947	94,129	$ 93,487	$ 98,118	$ 74,056	440,814	359,790	$ 278,019
Cost of sales									87,265	70,979	33,450
Net revenue									353,549	288,811	244,569
Canada
Long Lived Assets and Pre-Tax Income by Geographical Information
Stream and royalty interests, net	1,073,653				1,038,258				1,073,653	1,038,258
Dominican Republic
Long Lived Assets and Pre-Tax Income by Geographical Information
Stream and royalty interests, net	543,256				588,502				543,256	588,502
Chile
Long Lived Assets and Pre-Tax Income by Geographical Information
Stream and royalty interests, net	802,147				823,525				802,147	823,525
Africa
Long Lived Assets and Pre-Tax Income by Geographical Information
Stream and royalty interests, net	124,332				89,293				124,332	89,293
Mexico
Long Lived Assets and Pre-Tax Income by Geographical Information
Stream and royalty interests, net	105,889				118,899				105,889	118,899
United States
Long Lived Assets and Pre-Tax Income by Geographical Information
Stream and royalty interests, net	168,378				102,385				168,378	102,385
Australia
Long Lived Assets and Pre-Tax Income by Geographical Information
Stream and royalty interests, net	37,409				42,547				37,409	42,547
Other
Long Lived Assets and Pre-Tax Income by Geographical Information
Stream and royalty interests, net	37,192				44,678				37,192	44,678
Stream interest
Long Lived Assets and Pre-Tax Income by Geographical Information
Stream and royalty interests, net	1,879,859				1,868,715				1,879,859	1,868,715
Revenue									314,011	238,028	94,104
Cost of sales									87,265	70,979	33,450
Net revenue									226,746	167,049	60,654
Stream interest | Canada
Long Lived Assets and Pre-Tax Income by Geographical Information
Stream and royalty interests, net	852,035				809,692				852,035	809,692
Revenue									136,736	125,755	94,104
Cost of sales									45,954	47,417	33,450
Net revenue									90,782	78,338	60,654
Stream interest | Dominican Republic
Long Lived Assets and Pre-Tax Income by Geographical Information
Stream and royalty interests, net	543,256				588,502				543,256	588,502
Revenue									91,589	39,684
Cost of sales									27,191	11,625
Net revenue									64,398	28,059
Stream interest | Chile
Long Lived Assets and Pre-Tax Income by Geographical Information
Stream and royalty interests, net	348,778				369,896				348,778	369,896
Revenue									60,251	49,243
Cost of sales									9,037	7,280
Net revenue									51,214	41,963
Stream interest | Africa
Long Lived Assets and Pre-Tax Income by Geographical Information
Stream and royalty interests, net	123,760				88,596				123,760	88,596
Revenue									25,435	23,346
Cost of sales									5,083	4,657
Net revenue									20,352	18,689
Stream interest | Other
Long Lived Assets and Pre-Tax Income by Geographical Information
Stream and royalty interests, net	12,030				12,029				12,030	12,029
Royalty interest
Long Lived Assets and Pre-Tax Income by Geographical Information
Stream and royalty interests, net	1,012,397				979,372				1,012,397	979,372
Revenue									126,803	121,762	183,915
Net revenue									126,803	121,762	183,915
Royalty interest | Canada
Long Lived Assets and Pre-Tax Income by Geographical Information
Stream and royalty interests, net	221,618				228,566				221,618	228,566
Revenue									23,208	30,676	37,496
Net revenue									23,208	30,676	37,496
Royalty interest | Chile
Long Lived Assets and Pre-Tax Income by Geographical Information
Stream and royalty interests, net	453,369				453,629				453,369	453,629
Revenue									1,648	84	39,508
Net revenue									1,648	84	39,508
Royalty interest | Africa
Long Lived Assets and Pre-Tax Income by Geographical Information
Stream and royalty interests, net	572				697				572	697
Revenue									3,131	1,868	3,075
Net revenue									3,131	1,868	3,075
Royalty interest | Mexico
Long Lived Assets and Pre-Tax Income by Geographical Information
Stream and royalty interests, net	105,889				118,899				105,889	118,899
Revenue									41,945	35,267	43,008
Net revenue									41,945	35,267	43,008
Royalty interest | United States
Long Lived Assets and Pre-Tax Income by Geographical Information
Stream and royalty interests, net	168,378				102,385				168,378	102,385
Revenue									35,282	35,483	42,675
Net revenue									35,282	35,483	42,675
Royalty interest | Australia
Long Lived Assets and Pre-Tax Income by Geographical Information
Stream and royalty interests, net	37,409				42,547				37,409	42,547
Revenue									12,943	10,462	8,494
Net revenue									12,943	10,462	8,494
Royalty interest | Other
Long Lived Assets and Pre-Tax Income by Geographical Information
Stream and royalty interests, net	$ 25,162				$ 32,649				25,162	32,649
Revenue									8,646	7,922	9,659
Net revenue									$ 8,646	$ 7,922	$ 9,659