Annual report pursuant to Section 13 and 15(d)

SENIOR AND CONVERTIBLE SENIOR NOTES - Narrative (Details)

v3.6.0.2
SENIOR AND CONVERTIBLE SENIOR NOTES - Narrative (Details) - USD ($)
1 Months Ended
Sep. 30, 2012
Dec. 31, 2016
Dec. 31, 2015
Jun. 02, 2015
Nov. 30, 2013
Mar. 31, 2013
Apr. 30, 2012
Dec. 31, 2010
Debt Instrument [Line Items]                
Percentage of wholly owned subsidiary   100.00%            
Senior Notes [Member] | 7.15% senior notes due 2020 [Member]                
Debt Instrument [Line Items]                
Aggregate principal amount of offering               $ 200,000,000
Debt instrument, stated rate   7.15% 7.15%         7.15%
Percent of debt instrument par value issued         106.699%     97.567%
Add-on to existing 7.50% senior notes         $ 100,000,000      
Effective percentage of debt instrument         5.875%     7.50%
Senior Notes [Member] | 1.875% convertible senior notes due 2032 [Member]                
Debt Instrument [Line Items]                
Aggregate principal amount of offering $ 126,500,000              
Debt instrument, stated rate 1.875% 1.875% 1.875%          
Debt instrument, convertible, conversion ratio 0.0171985000              
Debt instrument, convertible, conversion price (in dollars per share) $ 58.14              
Debt instrument, convertible, conversion premium 47.50%              
Percentage of principal in the event of a repurchase 100.00%              
Senior Notes [Member] | 1.875% convertible senior notes due 2032 [Member] | Fifth anniversary [Member]                
Debt Instrument [Line Items]                
Debt instrument, convertible, conversion price (in dollars per share) $ 58.14              
Senior Notes [Member] | 1.875% convertible senior notes due 2032 [Member] | Tenth anniversary [Member]                
Debt Instrument [Line Items]                
Debt instrument, convertible, conversion price (in dollars per share) 58.14              
Senior Notes [Member] | 1.875% convertible senior notes due 2032 [Member] | Fifteenth anniversary [Member]                
Debt Instrument [Line Items]                
Debt instrument, convertible, conversion price (in dollars per share) $ 58.14              
Senior Notes [Member] | 7.00% senior notes due 2022 [Member]                
Debt Instrument [Line Items]                
Aggregate principal amount of offering             $ 300,000,000  
Debt instrument, stated rate   7.00% 7.00%       7.00%  
Senior Notes [Member] | 6.25% senior notes due 2015 [Member]                
Debt Instrument [Line Items]                
Debt instrument, stated rate             6.25%  
Aggregate principal amount repurchased             $ 285,000,000  
Senior Notes [Member] | 7.731% senior subordinated notes due 2017 [Member]                
Debt Instrument [Line Items]                
Debt instrument, stated rate             7.731%  
Aggregate principal amount repurchased           $ 99,800,000 $ 26,100,000  
Senior Notes [Member] | 4.50% senior notes due 2018 [Member]                
Debt Instrument [Line Items]                
Aggregate principal amount of offering           $ 175,000,000    
Debt instrument, stated rate   4.50% 4.50%     4.50%    
Senior Notes [Member] | 6.00% senior notes due 2025 [Member]                
Debt Instrument [Line Items]                
Aggregate principal amount of offering       $ 200,000,000.0        
Debt instrument, stated rate   6.00% 6.00% 6.00%