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Long-Term Debt - 4.25 Convertible Senior Notes (Details 7)
$ / shares in Units, shares in Millions
 1 Months Ended 12 Months Ended
Jun. 30, 2014
USD ($)
$ / shares
shares
Jun. 30, 2009
USD ($)
$ / shares
Dec. 31, 2015
USD ($)
Dec. 31, 2014
USD ($)
shares
Dec. 31, 2013
USD ($)
Dec. 04, 2015
USD ($)
Long-Term Debt            
Principle amount of senior notes           $ 350,000,000.0
Amortization of debt discount     $ 1,170,000 $ 12,380,000 $ 23,407,000  
Value of shares acquired upon exercise of call options     $ 0 89,407,000 0  
4.25% convertible senior notes due June 2014            
Long-Term Debt            
Principle amount of senior notes   $ 355,000,000.0        
Interest rate (as a percent)   4.25%        
Conversion rate of debt instrument (Shares per USD)   0.435084        
Face value rate of conversion   1,000        
Conversion price per common stock shares (in dollars per share) | $ / shares   $ 22.98        
Repayment of long term debt $ 370,000,000          
Number of shares of common stock issued upon redemption of debt | shares 6.8          
Amount of unamortized discount of notes   $ 97,900,000        
Recognized interest expense related to the contractual interest coupon       6,900,000 15,100,000  
Amortization of debt discount       $ 11,300,000 $ 23,000,000  
Effective interest rate (as a percent)   11.67%        
Price per share of common stock for call options purchased (in dollars per share) | $ / shares $ 22.98          
Warrant exercise price (in dollars per share) | $ / shares 32.19          
Effective conversion price (in dollars per share) | $ / shares $ 32.19          
Debt instrument face amount for effective conversion price $ 325,000,000          
Number of shares acquired upon exercise of call options | shares 6.5          
Value of shares acquired upon exercise of call options $ 89,400,000          
Trading days within which counterparties have the right to exercise warrants 80 days          
Common shares issued pursuant to warrants exercised | shares       1.6