Fee Revenue - Additional Information (Details 1) - USD ($) $ in Millions	6 Months Ended
	Oct. 31, 2019	Jan. 31, 2020
Revenue Remaining Performance Obligation Expected Timing Of Satisfaction [Line Items]
Revenue recognized, remaining performance obligation		$ 596.1
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date: 2020-02-01
Revenue Remaining Performance Obligation Expected Timing Of Satisfaction [Line Items]
Revenue recognized, remaining performance obligation		$ 122.0
Revenue, remaining performance obligation, expected timing of satisfaction, period		3 months
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date: 2020-05-01
Revenue Remaining Performance Obligation Expected Timing Of Satisfaction [Line Items]
Revenue recognized, remaining performance obligation		$ 263.6
Revenue, remaining performance obligation, expected timing of satisfaction, period		1 year
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		$ 117.2
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		$ 93.3
Revenue, remaining performance obligation, expected timing of satisfaction, period
Revenue, remaining performance obligation, expected timing of satisfaction, explanation	2023 and thereafter