Annual report pursuant to Section 13 and 15(d)

Accounts Receivable, Net (Details)

v3.21.2
Accounts Receivable, Net (Details) - USD ($)
$ in Thousands
 12 Months Ended
Sep. 30, 2021
Sep. 30, 2020
Sep. 30, 2019
Accounts, Notes, Loans and Financing Receivable [Line Items]      
Allowance for credit losses $ (8,044) $ (6,051)  
Accounts receivable, net 834,819 786,203  
Accounts Receivable, Allowance for Credit Loss [Roll Forward]      
Balance at beginning of period 6,051 5,382 $ 4,285
Provision for estimated credit losses 11,038 12,976 4,018
Write-offs, net of recoveries (9,045) (12,307) (2,921)
Balance at end of period 8,044 6,051 $ 5,382
Billed and billable receivables      
Accounts, Notes, Loans and Financing Receivable [Line Items]      
Accounts Receivable Gross 718,728 628,922  
Unbilled receivables      
Accounts, Notes, Loans and Financing Receivable [Line Items]      
Accounts Receivable Gross $ 124,135 $ 163,332