LONG-TERM DEBT- Components of Convertible Debt (Details) - USD ($)	Mar. 31, 2016	Dec. 31, 2015	Aug. 10, 2015
Liability component
Net carrying amount	$ 1,540,940,000	$ 1,449,178,000
Convertible Senior Notes | 1.5% Convertible Senior Notes, Due 2020
Liability component
Principal	287,500,000	287,500,000	$ 287,500,000.0
Conversion feature	(44,039,000)	(46,271,000)
Discount related to debt issuance costs	(5,880,000)	(6,144,000)
Net carrying amount	237,581,000	235,085,000
Equity component
Conversion feature	49,680,000	49,680,000
Debt issuance costs	(1,421,000)	(1,421,000)
Deferred taxes	(17,750,000)	(17,750,000)
Net amount recorded in additional paid-in capital	$ 30,509,000	$ 30,509,000