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Summary Of Significant Accounting Policies (Property And Equipment) (Details) - USD ($)
$ in Thousands
12 Months Ended
Sep. 30, 2018
Sep. 30, 2017
Sep. 30, 2016
Property, Plant and Equipment [Line Items]      
Computer equipment $ 194,847 $ 177,235  
Office furniture and equipment 31,625 32,781  
Leasehold improvements 107,615 88,410  
Property and equipment, gross 334,087 298,426  
Accumulated depreciation and amortization (189,045) (176,006)  
Property and equipment, net 145,042 122,420  
Depreciation and amortization expense $ 45,900 $ 44,600 $ 36,400
Minimum [Member]      
Property, Plant and Equipment [Line Items]      
Property and equipment, useful life 2 years    
Maximum [Member]      
Property, Plant and Equipment [Line Items]      
Property and equipment, useful life 5 years