SEGMENT INFORMATION (Details) $ in Thousands	3 Months Ended		9 Months Ended
	Mar. 31, 2020 USD ($)	Mar. 31, 2019 USD ($)	Mar. 31, 2020 USD ($) segment	Mar. 31, 2019 USD ($)	Jun. 30, 2019 USD ($)
Long Lived Assets and Pre-Tax Income by Geographical Information
Number of reportable segments | segment			2
Stream and royalty interests, net	$ 2,317,413		$ 2,317,413		$ 2,339,316
Revenue	136,437	$ 109,778	378,853	$ 307,362
Cost of sales	21,961	19,075	63,149	53,764
Production taxes	851	1,006	2,934	3,206
Depletion	51,115	39,316	129,758	120,580
Total segment gross profit	62,510	50,381	183,012	129,812
Canada
Long Lived Assets and Pre-Tax Income by Geographical Information
Stream and royalty interests, net	916,617		916,617		968,000
Dominican Republic
Long Lived Assets and Pre-Tax Income by Geographical Information
Stream and royalty interests, net	417,295		417,295		451,585
Chile
Long Lived Assets and Pre-Tax Income by Geographical Information
Stream and royalty interests, net	505,781		505,781		515,733
Africa
Long Lived Assets and Pre-Tax Income by Geographical Information
Stream and royalty interests, net	169,691		169,691		89,876
Mexico
Long Lived Assets and Pre-Tax Income by Geographical Information
Stream and royalty interests, net	77,694		77,694		83,748
United States
Long Lived Assets and Pre-Tax Income by Geographical Information
Stream and royalty interests, net	161,223		161,223		163,398
Australia
Long Lived Assets and Pre-Tax Income by Geographical Information
Stream and royalty interests, net	30,376		30,376		31,944
Rest of world
Long Lived Assets and Pre-Tax Income by Geographical Information
Stream and royalty interests, net	38,736		38,736		35,032
Stream interests
Long Lived Assets and Pre-Tax Income by Geographical Information
Stream and royalty interests, net	1,604,192		1,604,192		1,622,435
Revenue	97,460	77,765	274,065	215,480
Cost of sales	21,961	19,075	63,149	53,764
Depletion	43,240	31,061	106,883	91,794
Total segment gross profit	32,259	27,629	104,033	69,922
Stream interests | Canada
Long Lived Assets and Pre-Tax Income by Geographical Information
Stream and royalty interests, net	724,808		724,808		767,749
Revenue	37,136	34,012	112,990	81,021
Stream interests | Dominican Republic
Long Lived Assets and Pre-Tax Income by Geographical Information
Stream and royalty interests, net	417,295		417,295		451,585
Revenue	28,302	20,787	73,534	58,504
Stream interests | Chile
Long Lived Assets and Pre-Tax Income by Geographical Information
Stream and royalty interests, net	280,681		280,681		301,507
Revenue	22,055	15,638	63,323	51,016
Stream interests | Africa
Long Lived Assets and Pre-Tax Income by Geographical Information
Stream and royalty interests, net	169,370		169,370		89,555
Revenue	9,967	7,328	24,218	24,939
Stream interests | Rest of world
Long Lived Assets and Pre-Tax Income by Geographical Information
Stream and royalty interests, net	12,038		12,038		12,039
Royalty interests
Long Lived Assets and Pre-Tax Income by Geographical Information
Stream and royalty interests, net	713,221		713,221		716,881
Revenue	38,977	32,013	104,788	91,882
Production taxes	851	1,006	2,934	3,206
Depletion	7,875	8,255	22,875	28,786
Total segment gross profit	30,251	22,752	78,979	59,890
Royalty interests | Canada
Long Lived Assets and Pre-Tax Income by Geographical Information
Stream and royalty interests, net	191,809		191,809		200,251
Revenue	9,126	8,201	26,084	25,918
Royalty interests | Chile
Long Lived Assets and Pre-Tax Income by Geographical Information
Stream and royalty interests, net	225,100		225,100		214,226
Royalty interests | Africa
Long Lived Assets and Pre-Tax Income by Geographical Information
Stream and royalty interests, net	321		321		321
Revenue	925	161	2,531	1,185
Royalty interests | Mexico
Long Lived Assets and Pre-Tax Income by Geographical Information
Stream and royalty interests, net	77,694		77,694		83,748
Revenue	9,160	8,719	24,923	24,551
Royalty interests | United States
Long Lived Assets and Pre-Tax Income by Geographical Information
Stream and royalty interests, net	161,223		161,223		163,398
Revenue	13,199	9,813	33,813	24,153
Royalty interests | Australia
Long Lived Assets and Pre-Tax Income by Geographical Information
Stream and royalty interests, net	30,376		30,376		31,944
Revenue	3,714	3,234	11,062	9,451
Royalty interests | Rest of world
Long Lived Assets and Pre-Tax Income by Geographical Information
Stream and royalty interests, net	26,698		26,698		$ 22,993
Revenue	$ 2,853	$ 1,885	$ 6,375	$ 6,624