Revenue Recognition - Summary of Changes in Allowance for Credit Losses (Detail) $ in Thousands	6 Months Ended
Mar. 31, 2021 USD ($)
Revenue From Contract With Customer [Abstract]
Balance at September 30, 2020	$ 6,121
Current period provision	256
Write-offs, net and other	(580)
Balance as of March 31, 2021	$ 5,797

Amount of allowance for credit loss on financing receivable. Excludes allowance for financing receivable covered under loss sharing agreement.

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Name:	us-gaap_FinancingReceivableAllowanceForCreditLosses
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant