Annual report pursuant to Section 13 and 15(d)

FAIR VALUE MEASUREMENTS Fair Value Measurements (Narrative) (Details)

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FAIR VALUE MEASUREMENTS Fair Value Measurements (Narrative) (Details)
$ in Millions
Dec. 31, 2017
USD ($)
Dec. 31, 2016
USD ($)
Oct. 31, 2016
Dec. 31, 2015
Debt Fair Value [Line Items]        
Put option specific events trigger put option certain to occur 1      
5.375% Senior Notes due 2022 [Member]        
Debt Fair Value [Line Items]        
Interest rate, stated percentage 5.375%      
4.875% Senior Notes Due 2024 [Member]        
Debt Fair Value [Line Items]        
Interest rate, stated percentage 4.875%   4.875%  
2.5% Convertible Senior Notes Due 2019 [Member]        
Debt Fair Value [Line Items]        
Interest rate, stated percentage 2.50% 2.50%   2.50%
Fixed Rate Debt With Noncontrolling Interest Partner [Member]        
Estimate of fair value not practicable [Abstract]        
Face amount of debt $ 44.0 $ 35.7    
Level 3 [Member]        
Debt Fair Value [Line Items]        
Third party put option to sell its noncontrolling interest 1      
Level 2 [Member] | 5.375% Senior Notes due 2022 [Member]        
Debt Fair Value [Line Items]        
Interest rate, stated percentage 5.375% 5.375%    
Estimated fair values of senior notes $ 259.2 $ 259.7    
Level 2 [Member] | 4.875% Senior Notes Due 2024 [Member]        
Debt Fair Value [Line Items]        
Interest rate, stated percentage 4.875% 4.875%    
Estimated fair values of senior notes $ 592.3 $ 578.5    
Level 2 [Member] | 2.5% Convertible Senior Notes Due 2019 [Member]        
Debt Fair Value [Line Items]        
Interest rate, stated percentage 2.50% 2.50%    
Estimated fair values of convertible senior notes $ 310.6 $ 294.6