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Summary of Operations and Significant Accounting Policies - Advertising Expense - Additional Information (Details) - USD ($)
$ in Millions
12 Months Ended
Sep. 30, 2021
Sep. 30, 2020
Sep. 30, 2019
Organization Consolidation And Presentation Of Financial Statements [Abstract]      
Advertising expense $ 0.2 $ 0.3 $ 0.4