Fee Revenue - Additional Information (Details 1) $ in Millions	9 Months Ended
	Jan. 31, 2021 USD ($)
Revenue Remaining Performance Obligation Expected Timing Of Satisfaction [Line Items]
Revenue recognized, remaining performance obligation	$ 717.1
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date: 2021-02-01
Revenue Remaining Performance Obligation Expected Timing Of Satisfaction [Line Items]
Revenue recognized, remaining performance obligation	$ 132.6
Revenue, remaining performance obligation, expected timing of satisfaction, period	3 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	$ 337.0
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	$ 148.5
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	$ 99.0
Revenue, remaining performance obligation, expected timing of satisfaction, period
Revenue, remaining performance obligation, expected timing of satisfaction, explanation	2024 and thereafter