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, 2018 USD ($)	Mar. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Sep. 30, 2017 USD ($)	Jun. 30, 2017 USD ($)	Mar. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Sep. 30, 2016 USD ($)	Jun. 30, 2018 USD ($) segment	Jun. 30, 2017 USD ($)	Jun. 30, 2016 USD ($)
Long Lived Assets and Pre-Tax Income by Geographical Information
Number of reportable segments | segment									2
Impairments	$ (239,364)								$ (239,364)
Stream and royalty interests, net (Note 4)	2,501,117				$ 2,892,256				2,501,117	$ 2,892,256
Revenue	116,235	$ 115,983	$ 114,348	$ 112,476	108,934	$ 106,972	$ 106,961	$ 117,947	459,042	440,814	$ 359,790
Cost of sales									83,839	87,265	70,979
Net revenue									375,203	353,549	288,811
Canada
Long Lived Assets and Pre-Tax Income by Geographical Information
Impairments	(284)								(284)
Stream and royalty interests, net (Note 4)	1,023,778				1,073,653				1,023,778	1,073,653
Dominican Republic
Long Lived Assets and Pre-Tax Income by Geographical Information
Stream and royalty interests, net (Note 4)	495,460				543,256				495,460	543,256
Chile
Long Lived Assets and Pre-Tax Income by Geographical Information
Impairments	(239,080)								(239,080)
Stream and royalty interests, net (Note 4)	542,557				802,147				542,557	802,147
Africa
Long Lived Assets and Pre-Tax Income by Geographical Information
Stream and royalty interests, net (Note 4)	105,376				124,332				105,376	124,332
Mexico
Long Lived Assets and Pre-Tax Income by Geographical Information
Stream and royalty interests, net (Note 4)	93,277				105,889				93,277	105,889
United States
Long Lived Assets and Pre-Tax Income by Geographical Information
Stream and royalty interests, net (Note 4)	165,543				168,378				165,543	168,378
Australia
Long Lived Assets and Pre-Tax Income by Geographical Information
Stream and royalty interests, net (Note 4)	34,254				37,409				34,254	37,409
Other
Long Lived Assets and Pre-Tax Income by Geographical Information
Stream and royalty interests, net (Note 4)	40,872				37,192				40,872	37,192
Stream interest
Long Lived Assets and Pre-Tax Income by Geographical Information
Stream and royalty interests, net (Note 4)	1,750,204				1,879,859				1,750,204	1,879,859
Revenue									324,516	314,011	238,028
Cost of sales									83,839	87,265	70,979
Net revenue									240,677	226,746	167,049
Stream interest | Canada
Long Lived Assets and Pre-Tax Income by Geographical Information
Stream and royalty interests, net (Note 4)	809,500				852,035				809,500	852,035
Revenue									142,244	136,736	125,755
Cost of sales									40,766	45,954	47,417
Net revenue									101,478	90,782	78,338
Stream interest | Dominican Republic
Long Lived Assets and Pre-Tax Income by Geographical Information
Stream and royalty interests, net (Note 4)	495,460				543,256				495,460	543,256
Revenue									95,055	91,589	39,684
Cost of sales									28,496	27,191	11,625
Net revenue									66,559	64,398	28,059
Stream interest | Chile
Long Lived Assets and Pre-Tax Income by Geographical Information
Stream and royalty interests, net (Note 4)	328,331				348,778				328,331	348,778
Revenue									57,413	60,251	49,243
Cost of sales									8,614	9,037	7,280
Net revenue									48,799	51,214	41,963
Stream interest | Africa
Long Lived Assets and Pre-Tax Income by Geographical Information
Stream and royalty interests, net (Note 4)	104,874				123,760				104,874	123,760
Revenue									29,804	25,435	23,346
Cost of sales									5,963	5,083	4,657
Net revenue									23,841	20,352	18,689
Stream interest | Other
Long Lived Assets and Pre-Tax Income by Geographical Information
Stream and royalty interests, net (Note 4)	12,039				12,030				12,039	12,030
Royalty interest
Long Lived Assets and Pre-Tax Income by Geographical Information
Stream and royalty interests, net (Note 4)	990,277				1,012,397				990,277	1,012,397
Revenue									134,526	126,803	121,762
Net revenue									134,526	126,803	121,762
Royalty interest | Canada
Long Lived Assets and Pre-Tax Income by Geographical Information
Stream and royalty interests, net (Note 4)	214,562				221,618				214,562	221,618
Revenue									24,254	23,208	30,676
Net revenue									24,254	23,208	30,676
Royalty interest | Chile
Long Lived Assets and Pre-Tax Income by Geographical Information
Stream and royalty interests, net (Note 4)	453,306				453,369				453,306	453,369
Revenue									473	1,648	84
Net revenue									473	1,648	84
Royalty interest | Africa
Long Lived Assets and Pre-Tax Income by Geographical Information
Stream and royalty interests, net (Note 4)	502				572				502	572
Revenue									2,098	3,131	1,868
Net revenue									2,098	3,131	1,868
Royalty interest | Mexico
Long Lived Assets and Pre-Tax Income by Geographical Information
Stream and royalty interests, net (Note 4)	93,277				105,889				93,277	105,889
Revenue									42,959	41,945	35,267
Net revenue									42,959	41,945	35,267
Royalty interest | United States
Long Lived Assets and Pre-Tax Income by Geographical Information
Stream and royalty interests, net (Note 4)	165,543				168,378				165,543	168,378
Revenue									39,496	35,282	35,483
Net revenue									39,496	35,282	35,483
Royalty interest | Australia
Long Lived Assets and Pre-Tax Income by Geographical Information
Stream and royalty interests, net (Note 4)	34,254				37,409				34,254	37,409
Revenue									13,710	12,943	10,462
Net revenue									13,710	12,943	10,462
Royalty interest | Other
Long Lived Assets and Pre-Tax Income by Geographical Information
Stream and royalty interests, net (Note 4)	$ 28,833				$ 25,162				28,833	25,162
Revenue									11,536	8,646	7,922
Net revenue									$ 11,536	$ 8,646	$ 7,922