Fee Revenue - Schedule of Disaggregation of Fee Revenue by Industry (Detail) - USD ($) $ in Thousands	3 Months Ended
	Jul. 31, 2019	Jul. 31, 2018
Disaggregation Of Revenue [Line Items]
Fee Revenue	$ 496,198	$ 478,362
Industrial
Disaggregation Of Revenue [Line Items]
Fee Revenue	$ 139,907	$ 135,730
Fee Revenue, Percentage	28.90%	29.10%
Financial Services
Disaggregation Of Revenue [Line Items]
Fee Revenue	$ 86,876	$ 81,390
Fee Revenue, Percentage	17.90%	17.50%
Life Sciences/ Healthcare
Disaggregation Of Revenue [Line Items]
Fee Revenue	$ 82,114	$ 79,160
Fee Revenue, Percentage	16.90%	17.00%
Consumer Goods
Disaggregation Of Revenue [Line Items]
Fee Revenue	$ 71,833	$ 71,586
Fee Revenue, Percentage	14.80%	15.40%
Technology
Disaggregation Of Revenue [Line Items]
Fee Revenue	$ 69,095	$ 62,819
Fee Revenue, Percentage	14.30%	13.50%
Education/Non-Profit
Disaggregation Of Revenue [Line Items]
Fee Revenue	$ 30,761	$ 30,579
Fee Revenue, Percentage	6.40%	6.60%
General
Disaggregation Of Revenue [Line Items]
Fee Revenue	$ 3,963	$ 4,304
Fee Revenue, Percentage	0.80%	0.90%
Fee Revenue
Disaggregation Of Revenue [Line Items]
Fee Revenue	$ 484,549	$ 465,568
Fee Revenue, Percentage	100.00%	100.00%