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Long-Term Debt - Convertible Senior Notes Due 2023 (Details)
$ / shares in Units, $ in Thousands
12 Months Ended
Dec. 31, 2019
USD ($)
Mar. 20, 2018
USD ($)
$ / shares
Dec. 31, 2019
USD ($)
Dec. 31, 2018
USD ($)
Dec. 31, 2017
USD ($)
Debt Instrument [Line Items]          
Principal amount $ 436,146   $ 436,146    
Unamortized debt discount (22,540)   (22,540) $ (28,802)  
Interest expense     31,186 32,617 $ 38,274
Convertible Senior Notes Maturing September 2023          
Debt Instrument [Line Items]          
Principal amount 125,000 $ 125,000 125,000 125,000  
Interest rate (as a percent)   4.125%      
Frequency of periodic payment   semi-annually      
Maturity date   Sep. 15, 2023      
Initial conversion ratio   0.1056133      
Initial conversion price per share (in dollars per share) | $ / shares   $ 9.47      
If-converted value in excess of principal amount 2,100        
Redemption price as a percentage of principal amount   100.00%      
Minimum percentage in aggregate principal amount   25.00%      
Unamortized debt discount $ (14,541) $ (20,100) (14,541) (17,800)  
Carrying amount of equity component   $ 15,900      
Effective interest rate (as a percent)   7.80%      
Interest expense     $ 8,400 $ 6,400