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Enterprise-wide Disclosures and Concentration of Business - Additional Information (Detail) - Net Operating Revenue
12 Months Ended
Sep. 30, 2020
Sep. 30, 2019
Sep. 30, 2018
Customer Concentration Risk | Customer One      
Concentration Risk [Line Items]      
Concentration risk, percentage 11.00%    
Customer Concentration Risk | Customer Two      
Concentration Risk [Line Items]      
Concentration risk, percentage 10.00%    
U.S. | Geographic Concentration Risk      
Concentration Risk [Line Items]      
Concentration risk, percentage 46.00% 45.00% 45.00%