Fee Revenue - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended
Jul. 31, 2018	Jul. 31, 2017
Disaggregation Of Revenue [Line Items]
Total revenue	$ 478,362	$ 414,917
Contract liabilities, revenue recognized	$ 66,500
Revenue, practical expedient, initial application and transition, completed contract, same reporting period	true
Revenue, remaining performance obligation, optional exemption, performance obligation	true
Adjustments Due to ASC 606 \| Accounting Standards Update 2014-09
Disaggregation Of Revenue [Line Items]
Total revenue	$ 200

Amount of revenue recognized that was previously included in balance of obligation to transfer good or service to customer for which consideration from customer has been received or is due.

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Amount, excluding tax collected from customer, of revenue from satisfaction of performance obligation by transferring promised good or service to customer. Tax collected from customer is tax assessed by governmental authority that is both imposed on and concurrent with specific revenue-producing transaction, including, but not limited to, sales, use, value added and excise.

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Indicates (true false) whether practical expedient was elected under initial application of retrospective method not to restate completed contract beginning and ending in same annual reporting period.

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Indicates (true false) whether optional exemption was applied not to disclose amount of transaction price allocated to and explanation of expected timing of revenue recognition for remaining performance obligation, when contract has expected duration of one year or less or right to consideration corresponds directly to performance completed.

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