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Fee Revenue - Additional Information (Detail)
$ in Millions
3 Months Ended
Jul. 31, 2019
USD ($)
Revenue From Contract With Customer [Abstract]  
Contract liabilities, revenue recognized $ 44.8
Revenue recognized, remaining performance obligation $ 556.7
Revenue, practical expedient, initial application and transition, completed contract, same reporting period true
Revenue, remaining performance obligation, optional exemption, performance obligation true