Annual report pursuant to Section 13 and 15(d)

Significant Accounting Policies - Stripping Costs (Details)

v3.21.2
Significant Accounting Policies - Stripping Costs (Details) - USD ($)
$ in Millions
12 Months Ended
Sep. 30, 2021
Sep. 30, 2020
Sep. 30, 2019
Accounting Policies [Abstract]      
Capitalized costs, pre-production stripping costs $ 2.7 $ 0.0  
Production costs, period cost $ 1.8 $ 1.3 $ 1.6