Quarterly report pursuant to Section 13 or 15(d)

Senior and Convertible Senior Notes (Details Textual)

v3.2.0.727
Senior and Convertible Senior Notes (Details Textual) - Senior Notes [Member] - USD ($)
6 Months Ended
Jun. 30, 2015
Jun. 02, 2015
Dec. 31, 2014
4.50% senior notes due 2018 [Member]      
Debt Instrument [Line Items]      
Debt Instrument, Interest Rate, Stated Percentage 4.50%   4.50%
7.15% senior notes due 2020 [Member]      
Debt Instrument [Line Items]      
Debt Instrument, Interest Rate, Stated Percentage 7.15%   7.15%
7.00% senior notes due 2022 [Member]      
Debt Instrument [Line Items]      
Debt Instrument, Interest Rate, Stated Percentage 7.00%   7.00%
6.00% senior notes due 2025 [Member]      
Debt Instrument [Line Items]      
Debt instrument, face amount   $ 200,000,000  
Debt Instrument, Interest Rate, Stated Percentage 6.00% 6.00%  
1.875% convertible senior notes due 2032 [Member]      
Debt Instrument [Line Items]      
Debt Instrument, Interest Rate, Stated Percentage 1.875%   1.875%
Debt instrument, convertible, conversion ratio 0.0171985    
Debt instrument, convertible, conversion price (in dollars per share) $ 58.14    
Conversion premium (percentage) 47.50%