LONG-TERM DEBT / INTEREST EXPENSE - Components of Convertible Debt (Details) - USD ($)	Jun. 30, 2017	Dec. 31, 2016
Liability component
Net carrying amount	$ 1,509,760,000	$ 1,540,453,000
Convertible Senior Notes | 1.5% Convertible Senior Notes, Due 2020
Liability component
Principal	287,500,000	287,500,000
Conversion feature	(32,445,000)	(37,179,000)
Discount related to debt issuance costs	(4,455,000)	(5,048,000)
Net carrying amount	$ 250,600,000	$ 245,273,000