Fee Revenue - Additional Information (Details 1) $ in Millions	6 Months Ended
	Oct. 31, 2020 USD ($)
Revenue Remaining Performance Obligation Expected Timing Of Satisfaction [Line Items]
Revenue recognized, remaining performance obligation	$ 679.2
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date: 2020-11-01
Revenue Remaining Performance Obligation Expected Timing Of Satisfaction [Line Items]
Revenue recognized, remaining performance obligation	$ 194.7
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	$ 260.5
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	$ 129.7
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	$ 94.3
Revenue, remaining performance obligation, expected timing of satisfaction, period
Revenue, remaining performance obligation, expected timing of satisfaction, explanation	2024 and thereafter