Accounts Receivable, Net (Tables)

12 Months Ended

Sep. 30, 2021

Receivables [Abstract]

Details of Accounts Receivable

Table 16.1: Details of Accounts Receivable, Net
	As of September 30,
	2021		2020
	(in thousands)
Billed and billable receivables	$	718,728	$	628,922
Unbilled receivables	124,135		163,332
Allowance for credit losses	(8,044)		(6,051)
Accounts receivable, net	$	834,819	$	786,203

Schedule of Accounts Receivable

Table 16.2: Changes in Allowance for Credit Losses
	For the Year Ended September 30,
	2021		2020		2019
	(in thousands)
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