v3.23.3
Borrowings - Components of Interest and Other Debt Expenses (Details) - USD ($)
$ in Millions
 12 Months Ended
Sep. 30, 2023
Sep. 30, 2022
Sep. 30, 2021
2025 Notes      
Debt Instrument [Line Items]      
Coupon interest $ 10.5 $ 10.5 $ 10.5
Amortization of financing costs and discount 1.3 1.3 1.3
Effect of interest rate swap 0.0 0.0 0.0
Total interest expense $ 11.8 $ 11.8 $ 11.8
Coupon interest rate 3.50% 3.50% 3.50%
2027 Notes      
Debt Instrument [Line Items]      
Coupon interest $ 9.5 $ 9.5 $ 3.5
Amortization of financing costs and discount 0.9 0.9 0.3
Effect of interest rate swap 13.4 (0.4) (1.1)
Total interest expense $ 23.8 $ 10.0 $ 2.7
Coupon interest rate 6.539% 2.585% 1.813%
2029 Notes      
Debt Instrument [Line Items]      
Coupon interest $ 2.7    
Amortization of financing costs and discount 0.2    
Effect of interest rate swap 0.6    
Total interest expense $ 3.5    
Coupon interest rate 8.49%