Annual report pursuant to Section 13 and 15(d)

LONG-TERM DEBT (2.5% Convertible Senior Notes Due 2019) (Details)

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LONG-TERM DEBT (2.5% Convertible Senior Notes Due 2019) (Details) - USD ($)
 3 Months Ended 12 Months Ended
Mar. 31, 2018
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Debt Instrument [Line Items]        
Adjustments to Additional Paid in Capital, Equity Component of Convertible Debt, Subsequent Adjustments   $ (92,641,000)    
Remaining notes balance   2,909,879,000 $ 2,337,992,000  
2.5% Convertible Senior Notes Due 2019 [Member]        
Debt Instrument [Line Items]        
Extinguishment of debt $ 246,300,000.0      
Interest rate, stated percentage 2.50%   2.50% 2.50%
Cost To Retire Outstanding Principal Of Convertible Senior Notes $ 336,700,000.0      
Rate Assumed To Calculate Fair Value Of Equity Component Extinguishment Of Debt 4.87%      
Adjustments to Additional Paid in Capital, Equity Component of Convertible Debt, Subsequent Adjustments $ 92,600,000.0      
Remaining notes balance   $ 28,673,000 $ 275,000,000