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Employee Stock Purchase Plan - Additional Information (Detail) - USD ($)
1 Months Ended 6 Months Ended
Feb. 28, 2019
Mar. 31, 2020
Sep. 30, 2019
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]      
Common stock, shares issued   27,717,663 27,508,473
Stock Purchase Plan [Member]      
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]      
Additional common shares authorized 500,000    
Common stock available for issuance   1,500,000  
Stock Purchase Plan, requisite continuous service   1 year  
Annual offerings description   implementation of annual offerings beginning on the first day of October in each of the years 2008 through 2027, with each offering terminating on September 30 of the following year.  
Closing price of common stock on the first and last day of the offering   85.00%  
Percentage not exceeding to periodic payment of purchase price   10.00%  
Maximum common stock value purchased by participant annually   $ 25,000  
Common stock, shares issued   591,663  
1998 Employee Stock Purchase Plan [Member]      
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]      
Additional Common Shares Authorized   52,837