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FAIR VALUE MEASUREMENTS - Additional Information (Details) - USD ($)
Dec. 31, 2016
Dec. 31, 2015
Debt Instrument [Line Items]    
Liabilities at fair value $ 0 $ 0
Convertible Notes Due 2017    
Debt Instrument [Line Items]    
Fair value of Convertible Notes 293,530,000 217,117,000
7.5% Senior Notes due 2022    
Debt Instrument [Line Items]    
Fair value of Senior Notes $ 465,000,000 $ 271,250,000