Revenue Recognition - Summary of Changes in Allowance for Credit Losses (Detail) $ in Thousands	12 Months Ended
	Sep. 30, 2021 USD ($)
Revenue From Contract With Customer [Abstract]
Balance at September 30, 2020	$ 6,121
Current period provision	(248)
Write-offs, net and other	(1,094)
Balance as of September 30, 2021	$ 4,779