Fee Revenue Classified by Country (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Apr. 30, 2016	Jan. 31, 2016	Oct. 31, 2015	Jul. 31, 2015	Apr. 30, 2015	Jan. 31, 2015	Oct. 31, 2014	Jul. 31, 2014	Apr. 30, 2016	Apr. 30, 2015	Apr. 30, 2014
Segment Reporting Information [Line Items]
Fee revenue	$ 399,960	$ 344,158	$ 280,600	$ 267,394	$ 271,717	$ 249,545	$ 255,702	$ 251,188	$ 1,292,112	$ 1,028,152	$ 960,301
UNITED STATES
Segment Reporting Information [Line Items]
Fee revenue									669,585	557,024	507,280
Other Countries
Segment Reporting Information [Line Items]
Fee revenue									$ 622,527	$ 471,128	$ 453,021