Fee Revenue - Additional Information (Details 1) $ in Millions	3 Months Ended
	Jul. 31, 2020 USD ($)
Revenue Remaining Performance Obligation Expected Timing Of Satisfaction [Line Items]
Revenue recognized, remaining performance obligation	$ 629.8
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date: 2020-08-01
Revenue Remaining Performance Obligation Expected Timing Of Satisfaction [Line Items]
Revenue recognized, remaining performance obligation	$ 247.3
Revenue, remaining performance obligation, expected timing of satisfaction, period	9 months
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date: 2021-05-01
Revenue Remaining Performance Obligation Expected Timing Of Satisfaction [Line Items]
Revenue recognized, remaining performance obligation	$ 210.0
Revenue, remaining performance obligation, expected timing of satisfaction, period	1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date: 2022-05-01
Revenue Remaining Performance Obligation Expected Timing Of Satisfaction [Line Items]
Revenue recognized, remaining performance obligation	$ 95.4
Revenue, remaining performance obligation, expected timing of satisfaction, period	1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date: 2023-05-01
Revenue Remaining Performance Obligation Expected Timing Of Satisfaction [Line Items]
Revenue recognized, remaining performance obligation	$ 77.1
Revenue, remaining performance obligation, expected timing of satisfaction, period
Revenue, remaining performance obligation, expected timing of satisfaction, explanation	2024 and thereafter