Segments - Fee Revenue Classified by Country (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Apr. 30, 2021	Jan. 31, 2021	Oct. 31, 2020	Jul. 31, 2020	Apr. 30, 2020	Jan. 31, 2020	Oct. 31, 2019	Jul. 31, 2019	Apr. 30, 2021	Apr. 30, 2020	Apr. 30, 2019
Segment Reporting Information [Line Items]
Total revenue									$ 1,819,946	$ 1,977,330	$ 1,973,862
Fee Revenue
Segment Reporting Information [Line Items]
Total revenue	$ 555,151	$ 475,360	$ 435,439	$ 344,097	$ 440,469	$ 515,325	$ 492,389	$ 484,549	1,810,047	1,932,732	1,926,033
Fee Revenue | UNITED STATES
Segment Reporting Information [Line Items]
Total revenue									837,682	875,605	859,969
Fee Revenue | United Kingdom
Segment Reporting Information [Line Items]
Total revenue									189,893	204,271	202,055
Fee Revenue | Other Countries
Segment Reporting Information [Line Items]
Total revenue									$ 782,472	$ 852,856	$ 864,009