FAIR VALUE MEASUREMENTS (Details) (USD $)	3 Months Ended
	Sep. 30, 2014
Recurring basis | Carrying Amount
Assets:
United States treasury bills	$ 499,991,000
Marketable equity securities	8,268,000
Liabilities:
Debt	391,333,000
Amount of equity component of convertible notes	77,000,000
Recurring basis | Fair Value
Assets:
United States treasury bills	499,991,000
Marketable equity securities	8,268,000
Total assets	508,259,000
Liabilities:
Debt	387,575,000
Total liabilities	387,575,000
Recurring basis | Level 1
Assets:
United States treasury bills	499,991,000
Marketable equity securities	8,268,000
Total assets	508,259,000
Liabilities:
Debt	387,575,000
Total liabilities	387,575,000
Impaired mining asset | Non-recurring basis | Fair Value
Assets:
Total assets	0
Number of properties	$ 2