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Long-Term Debt - Additional Information (Details) - USD ($)
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Sep. 30, 2016
Jun. 10, 2016
Apr. 30, 2016
Senior Notes | 2023 Notes              
Debt Instrument [Line Items]              
Debt instrument face amount           $ 645,000,000  
Debt instrument, percentage rate 9.25%     9.25%   9.25%  
Minimum percentage of notes held in order to cause acceleration of notes upon occurrence of events of default           25.00%  
Amount outstanding $ 645,000,000 $ 645,000,000          
Senior Notes | 2021 Notes              
Debt Instrument [Line Items]              
Debt instrument face amount             $ 320,000,000
Debt instrument, percentage rate 6.50%           6.50%
Amount outstanding $ 2,240,000 $ 2,240,000 $ 2,200,000        
Line of Credit | AB Credit Facility | Revolving credit facility              
Debt Instrument [Line Items]              
Debt instrument face amount         $ 50,000,000    
Available increase in borrowing limit         $ 25,000,000