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Long-Term Debt - Convertible Senior Notes Due 2022 (Details)
$ / shares in Units, $ in Thousands
1 Months Ended 12 Months Ended
Nov. 01, 2016
USD ($)
$ / shares
Mar. 31, 2012
USD ($)
Dec. 31, 2018
USD ($)
Dec. 31, 2017
USD ($)
Dec. 31, 2016
USD ($)
Debt Instrument [Line Items]          
Principal amount     $ 479,161    
Unamortized debt discount     (28,802) $ (14,406)  
Interest expense     32,617 38,274 $ 45,110
Convertible Senior Notes Maturing May 2022          
Debt Instrument [Line Items]          
Principal amount $ 125,000   125,000 125,000  
Interest rate (as a percent) 4.25%        
Frequency of periodic payment semi-annually        
Maturity date May 01, 2022        
Initial conversion ratio 0.0719748        
Initial conversion price per share (in dollars per share) | $ / shares $ 13.89        
Redemption price as a percentage of principal amount 100.00%        
Minimum percentage in aggregate principal amount 25.00%        
Unamortized debt discount $ (16,900)   (11,043) (13,900)  
Carrying amount of equity component $ 11,000        
Effective interest rate (as a percent) 7.30%        
Interest expense     8,100 7,900 $ 1,300
Convertible Senior Notes Maturing March 2032          
Debt Instrument [Line Items]          
Principal amount   $ 200,000 $ 0 $ 60,115  
Interest rate (as a percent)   3.25%      
Maturity date   Mar. 15, 2032