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Borrowings - Schedule of Debt Redemption (Details) - Senior Notes
12 Months Ended
Sep. 30, 2021
Sep. 30, 2019
Oct. 31, 2017
Mar. 31, 2017
6 3/4% Senior Notes (2025 Notes)        
Debt Instrument, Redemption [Line Items]        
Stated interest rate on debt instrument 6.75%     0.0675%
6 3/4% Senior Notes (2025 Notes) | Debt Instrument, Redemption, Period One        
Debt Instrument, Redemption [Line Items]        
Redemption price percentage 100.00%      
6 3/4% Senior Notes (2025 Notes) | Debt Instrument, Redemption, Period Two        
Debt Instrument, Redemption [Line Items]        
Redemption price percentage 105.063%      
6 3/4% Senior Notes (2025 Notes) | Debt Instrument, Redemption, Period Three        
Debt Instrument, Redemption [Line Items]        
Redemption price percentage 103.375%      
6 3/4% Senior Notes (2025 Notes) | Debt Instrument, Redemption, Period Four        
Debt Instrument, Redemption [Line Items]        
Redemption price percentage 101.688%      
6 3/4% Senior Notes (2025 Notes) | Debt Instrument, Redemption, Period Five        
Debt Instrument, Redemption [Line Items]        
Redemption price percentage 100.00%      
5 7/8% Senior Notes (2027 Notes)        
Debt Instrument, Redemption [Line Items]        
Stated interest rate on debt instrument 5.88%   0.0588%  
Redemption price percentage 105.875%      
Percentage of principal amount redeemed 35.00%      
Percentage of principal amount outstanding after redemption 65.00%      
5 7/8% Senior Notes (2027 Notes) | Debt Instrument, Redemption, Period One        
Debt Instrument, Redemption [Line Items]        
Redemption price percentage 100.00%      
5 7/8% Senior Notes (2027 Notes) | Debt Instrument, Redemption, Period Two        
Debt Instrument, Redemption [Line Items]        
Redemption price percentage 102.938%      
5 7/8% Senior Notes (2027 Notes) | Debt Instrument, Redemption, Period Three        
Debt Instrument, Redemption [Line Items]        
Redemption price percentage 101.958%      
5 7/8% Senior Notes (2027 Notes) | Debt Instrument, Redemption, Period Four        
Debt Instrument, Redemption [Line Items]        
Redemption price percentage 100.979%      
5 7/8% Senior Notes (2027 Notes) | Debt Instrument, Redemption, Period Five        
Debt Instrument, Redemption [Line Items]        
Redemption price percentage 100.00%      
7 1/4% Senior Notes Maturing October 2029        
Debt Instrument, Redemption [Line Items]        
Stated interest rate on debt instrument 7.25% 0.0725%    
Redemption price percentage 107.25%      
Percentage of principal amount redeemed 35.00%      
Percentage of principal amount outstanding after redemption 65.00%      
7 1/4% Senior Notes Maturing October 2029 | Debt Instrument, Redemption, Period One        
Debt Instrument, Redemption [Line Items]        
Redemption price percentage 100.00%      
7 1/4% Senior Notes Maturing October 2029 | Debt Instrument, Redemption, Period Two        
Debt Instrument, Redemption [Line Items]        
Redemption price percentage 103.625%      
7 1/4% Senior Notes Maturing October 2029 | Debt Instrument, Redemption, Period Three        
Debt Instrument, Redemption [Line Items]        
Redemption price percentage 102.417%      
7 1/4% Senior Notes Maturing October 2029 | Debt Instrument, Redemption, Period Four        
Debt Instrument, Redemption [Line Items]        
Redemption price percentage 101.208%      
7 1/4% Senior Notes Maturing October 2029 | Debt Instrument, Redemption, Period Five        
Debt Instrument, Redemption [Line Items]        
Redemption price percentage 100.00%