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Long-Term Debt - 7.875 Percent Convertible Notes (Details)
1 Months Ended 6 Months Ended
Oct. 16, 2020
USD ($)
Nov. 30, 2020
USD ($)
Mar. 31, 2021
USD ($)
Mar. 31, 2020
USD ($)
Sep. 30, 2020
USD ($)
Debt Instrument [Line Items]          
Redemption of convertible notes     $ 53,000,000 $ 0  
Loss on debt extinguishment     $ 8,000,000 $ 0  
7.875 percent convertible notes due 2026          
Debt Instrument [Line Items]          
Redemption of convertible notes $ 53,000,000        
Convertible Notes | 7.875 percent convertible notes due 2026          
Debt Instrument [Line Items]          
Interest rate (percent) 7.875%   7.875%    
Debt $ 23,000,000   $ 0   $ 23,000,000
Principal amount of convertible notes repurchased 23,000,000        
Debt instrument, repurchase amount in excess of accreted principal 30,000,000        
Loss on debt extinguishment $ 0        
Convertible Notes | 7.875 percent convertible notes due 2026 | Redemption Period One          
Debt Instrument [Line Items]          
Conversion ratio of common stock per principal   83.3333      
Principal amount per note for conversion   $ 1,000