Annual report pursuant to Section 13 and 15(d)

Significant Accounting Policies - Stripping Costs (Details)

v3.23.3
Significant Accounting Policies - Stripping Costs (Details) - USD ($)
$ in Millions
12 Months Ended
Sep. 30, 2023
Sep. 30, 2022
Sep. 30, 2021
Accounting Policies [Abstract]      
Capitalized costs, pre-production stripping costs $ 0.8 $ 3.9  
Production costs, period cost $ 3.1 $ 1.7 $ 1.8