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Shareholders' Equity and Stock-Based Compensation - Summary of Option Activity under Stock-Based Compensation Plan (Detail) - $ / shares
12 Months Ended
Sep. 30, 2020
Sep. 30, 2019
Sep. 30, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Number of Shares, Options exercised (20,000) (45,000)  
Number of Shares, Options outstanding 252,492 272,492 317,492
Average Exercise Price Per Share, Options exercised $ 5.126 $ 5.126  
Average Exercise Price Per Share, Options outstanding $ 6.205 $ 6.126 $ 5.984