Annual report pursuant to Section 13 and 15(d)

LONG-TERM DEBT (2.5% Convertible Senior Notes Due 2023) (Details)

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LONG-TERM DEBT (2.5% Convertible Senior Notes Due 2023) (Details)
12 Months Ended
Dec. 31, 2019
USD ($)
$ / shares
shares
Mar. 31, 2018
USD ($)
2.5% Convertible Senior Notes Due 2023 [Member]    
Debt Instrument [Line Items]    
Face amount $ 550,000,000 $ 550,000,000
Interest rate, stated percentage   2.50%
Conversion ratio 0.0147005  
Conversion Premium 54.40%  
Last reported sale price used to calculate conversion premium | $ / shares $ 44.05  
Maximum number of shares issuable upon conversion | shares 8,100,000  
Carrying amount of equity component $ 64,000,000.0  
Unamortized debt discount balance $ 42,400,000  
Debt discount amortization period 3 years  
Value of convertible notes, if fully settled in shares, exceeded the principal amount $ 27,900,000  
Effective interest rate 5.70%  
Debt instrument period payment of principal, percentage 2.50%  
2.5% Convertible Senior Notes Due 2023 [Member] | Redemption, Defined Changes of Control [Member]    
Debt Instrument [Line Items]    
Redemption price, percentage 100.00%  
2.5% Convertible Senior Notes Due 2019 and 2023 [Member]    
Debt Instrument [Line Items]    
Interest rate, stated percentage 2.50%