INCOME TAXES (Details) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Jun. 30, 2014	Sep. 30, 2013	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2013
Income before income taxes
United States			$ 17,569	$ 17,033	$ 65,851
Foreign			44,675	65,894	71,317
Income before income taxes			62,244	82,927	137,168
Current:
Federal			22,418	(3,663)	30,061
State			(36)	334	368
Foreign			14,835	30,950	44,749
Total current income tax expenses			37,217	27,621	75,178
Deferred and others:
Federal			(5,506)	(4,122)	(4,341)
State			(49)	(26)	(27)
Foreign			(22,096)	(4,018)	(7,051)
Total deferred and other income tax expenses			(27,651)	(8,166)	(11,419)
Total income tax expenses			9,566	19,455	63,759
Differences between provision for income taxes and income tax expense computed by applying federal rates
Total expense computed by applying federal rates			21,786	29,024	48,009
State and provincial income taxes, net of federal benefit			25	334	368
Excess depletion			(1,429)	(1,114)	(1,395)
Estimates for uncertain tax positions			1,404	(7,386)	1,868
Statutory tax attributable to non-controlling interest			(211)	(293)	(1,236)
Effect of foreign earnings			6,536	1,141	4,223
Effect of foreign earnings indefinitely reinvested			(7,601)	(1,700)
Effect of recognized loss on available-for-sale securities				562	4,239
Unrealized foreign exchange gains			(10,949)	(367)	1,146
Changes in estimates and corrected errors of prior year tax			(359)	(594)	4,979
Other			(1,225)	(152)	1,558
Total income tax expenses			9,566	19,455	63,759
Income tax (benefit) expense resulting from continued review of prior years tax accounts	$ 2,600	$ (1,700)
Deferred tax assets:
Stock-based compensation	3,511		4,393	3,511
Net operating losses	19,322		16,087	19,322
Other deferred tax assets	7,068		3,904	7,068
Total deferred tax assets	29,901		24,384	29,901
Valuation allowance	(4,933)		(4,262)	(4,933)
Net deferred tax assets	24,968		20,122	24,968
Deferred tax liabilities:
Mineral property basis	(158,301)		(133,646)	(158,301)
Unrealized foreign exchange gains	(3,072)			(3,072)
Unrealized foreign exchange losses			936
2019 Notes	(20,002)		(16,384)	(20,002)
Other deferred tax liabilities	(2,239)		(1,658)	(2,239)
Total deferred tax liabilities	(183,614)		(150,752)	(183,614)
Total deferred tax liabilities	(158,646)		(130,630)	(158,646)
Net operating loss carry forwards
Net operating loss carry forwards	77,000		55,000	77,000
Reconciliation of beginning and ending amount of gross unrecognized tax benefits
Total gross unrecognized tax benefits at beginning of year		$ 21,166	13,725	21,166	19,469
Additions / Reductions for tax positions of current year			1,662	(1,052)	2,638
Reductions due to settlements with taxing authorities			(257)	(296)	(941)
Reductions due to lapse of statute of limitations				(6,093)
Total amount of gross unrecognized tax benefits at end of year	13,725		$ 15,130	13,725	$ 21,166
Net unrecognized tax benefits
Expiration period of statute of limitations for income tax examinations			12 months
Accrued income-tax-related interest and penalties	$ 5,400		$ 4,600	$ 5,400
Canada
Differences between provision for income taxes and income tax expense computed by applying federal rates
Income tax rate adjustment/ reform			4,070
Chile
Differences between provision for income taxes and income tax expense computed by applying federal rates
Income tax rate adjustment/ reform			$ (2,481)