SEGMENT INFORMATION (Details) $ in Thousands	3 Months Ended		6 Months Ended
	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2017 USD ($) segment	Dec. 31, 2016 USD ($)	Jun. 30, 2017 USD ($)
Long Lived Assets and Pre-Tax Income by Geographical Information
Number of reportable segments | segment			2
Value of stream and royalty interests, net	$ 2,810,616		$ 2,810,616		$ 2,892,256
Revenue	114,348	$ 106,961	226,824	$ 224,909
Cost of sales	19,863	22,502	40,282	45,163
Net revenue	94,485	84,459	186,542	179,746
Canada
Long Lived Assets and Pre-Tax Income by Geographical Information
Value of stream and royalty interests, net	1,054,812		1,054,812		1,073,653
Dominican Republic
Long Lived Assets and Pre-Tax Income by Geographical Information
Value of stream and royalty interests, net	517,203		517,203		543,256
Chile
Long Lived Assets and Pre-Tax Income by Geographical Information
Value of stream and royalty interests, net	790,223		790,223		802,147
Africa
Long Lived Assets and Pre-Tax Income by Geographical Information
Value of stream and royalty interests, net	112,554		112,554		124,332
Mexico
Long Lived Assets and Pre-Tax Income by Geographical Information
Value of stream and royalty interests, net	99,769		99,769		105,889
United States
Long Lived Assets and Pre-Tax Income by Geographical Information
Value of stream and royalty interests, net	166,115		166,115		168,378
Australia
Long Lived Assets and Pre-Tax Income by Geographical Information
Value of stream and royalty interests, net	35,780		35,780		37,409
Other
Long Lived Assets and Pre-Tax Income by Geographical Information
Value of stream and royalty interests, net	34,160		34,160		37,192
Stream interest
Long Lived Assets and Pre-Tax Income by Geographical Information
Value of stream and royalty interests, net	1,814,245		1,814,245		1,879,859
Revenue	79,287	74,007	158,049	159,511
Cost of sales	19,863	22,502	40,282	45,163
Net revenue	59,424	51,505	117,767	114,348
Stream interest | Canada
Long Lived Assets and Pre-Tax Income by Geographical Information
Value of stream and royalty interests, net	836,129		836,129		852,035
Revenue	22,702	31,664	54,654	70,050
Cost of sales	6,624	11,181	15,847	23,758
Net revenue	16,078	20,483	38,807	46,292
Stream interest | Dominican Republic
Long Lived Assets and Pre-Tax Income by Geographical Information
Value of stream and royalty interests, net	517,203		517,203		543,256
Revenue	26,355	26,437	51,758	47,387
Cost of sales	8,198	8,547	15,785	14,443
Net revenue	18,157	17,890	35,973	32,944
Stream interest | Chile
Long Lived Assets and Pre-Tax Income by Geographical Information
Value of stream and royalty interests, net	336,854		336,854		348,778
Revenue	21,601	10,985	33,938	31,154
Cost of sales	3,297	1,746	5,109	4,744
Net revenue	18,304	9,239	28,829	26,410
Stream interest | Africa
Long Lived Assets and Pre-Tax Income by Geographical Information
Value of stream and royalty interests, net	112,029		112,029		123,760
Revenue	8,629	4,921	17,699	10,920
Cost of sales	1,744	1,028	3,541	2,218
Net revenue	6,885	3,893	14,158	8,702
Stream interest | Other
Long Lived Assets and Pre-Tax Income by Geographical Information
Value of stream and royalty interests, net	12,030		12,030		12,030
Royalty interest
Long Lived Assets and Pre-Tax Income by Geographical Information
Value of stream and royalty interests, net	996,371		996,371		1,012,397
Revenue	35,061	32,954	68,775	65,398
Net revenue	35,061	32,954	68,775	65,398
Royalty interest | Canada
Long Lived Assets and Pre-Tax Income by Geographical Information
Value of stream and royalty interests, net	218,683		218,683		221,618
Revenue	5,396	5,682	11,488	11,870
Net revenue	5,396	5,682	11,488	11,870
Royalty interest | Chile
Long Lived Assets and Pre-Tax Income by Geographical Information
Value of stream and royalty interests, net	453,369		453,369		453,369
Revenue				950
Net revenue				950
Royalty interest | Africa
Long Lived Assets and Pre-Tax Income by Geographical Information
Value of stream and royalty interests, net	525		525		572
Revenue	585	764	1,047	1,588
Net revenue	585	764	1,047	1,588
Royalty interest | Mexico
Long Lived Assets and Pre-Tax Income by Geographical Information
Value of stream and royalty interests, net	99,769		99,769		105,889
Revenue	10,854	11,530	21,751	21,127
Net revenue	10,854	11,530	21,751	21,127
Royalty interest | United States
Long Lived Assets and Pre-Tax Income by Geographical Information
Value of stream and royalty interests, net	166,115		166,115		168,378
Revenue	12,298	9,407	22,727	19,113
Net revenue	12,298	9,407	22,727	19,113
Royalty interest | Australia
Long Lived Assets and Pre-Tax Income by Geographical Information
Value of stream and royalty interests, net	35,780		35,780		37,409
Revenue	3,227	3,230	6,548	6,692
Net revenue	3,227	3,230	6,548	6,692
Royalty interest | Other
Long Lived Assets and Pre-Tax Income by Geographical Information
Value of stream and royalty interests, net	22,130		22,130		$ 25,162
Revenue	2,701	2,341	5,214	4,058
Net revenue	$ 2,701	$ 2,341	$ 5,214	$ 4,058