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Revenue - Summary of Accounts Receivable Billed and Unbilled and Deferred Revenue (Parenthetical) (Detail) - USD ($)
$ in Thousands
Sep. 30, 2019
Oct. 01, 2018
Sep. 30, 2018
Revenue from Contract with Customer [Abstract]      
Allowance for doubtful accounts $ 36,121 $ 21,211 $ 21,211