FAIR VALUE MEASUREMENTS (Details) (Recurring basis, USD $)	Dec. 31, 2014
Carrying Amount
Assets:
United States treasury bills	$ 524,983,000
Marketable equity securities	7,788,000
Liabilities:
Debt	393,874,000
Amount of equity component of convertible notes	77,000,000
Fair Value
Assets:
United States treasury bills	524,983,000
Marketable equity securities	7,788,000
Total assets	532,771,000
Liabilities:
Debt	382,957,000
Total liabilities	382,957,000
Level 1
Assets:
United States treasury bills	524,983,000
Marketable equity securities	7,788,000
Total assets	532,771,000
Liabilities:
Debt	382,957,000
Total liabilities	$ 382,957,000