Fee Revenue - Schedule of Disaggregation of Fee Revenue by Industry (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Jan. 31, 2020	Jan. 31, 2019	Jan. 31, 2020	Jan. 31, 2019
Disaggregation Of Revenue [Line Items]
Fee Revenue	$ 527,979	$ 486,172	$ 1,528,354	$ 1,471,327
Industrial
Disaggregation Of Revenue [Line Items]
Fee Revenue	$ 148,552	$ 138,460	$ 427,469	$ 418,159
Fee Revenue, Percentage	28.80%	29.20%	28.60%	29.10%
Financial Services
Disaggregation Of Revenue [Line Items]
Fee Revenue	$ 87,917	$ 86,570	$ 260,250	$ 260,975
Fee Revenue, Percentage	17.10%	18.20%	17.40%	18.20%
Life Sciences/ Healthcare
Disaggregation Of Revenue [Line Items]
Fee Revenue	$ 88,924	$ 76,654	$ 259,845	$ 239,425
Fee Revenue, Percentage	17.30%	16.20%	17.40%	16.70%
Consumer Goods
Disaggregation Of Revenue [Line Items]
Fee Revenue	$ 76,719	$ 74,186	$ 223,779	$ 224,848
Fee Revenue, Percentage	14.90%	15.60%	15.00%	15.70%
Technology
Disaggregation Of Revenue [Line Items]
Fee Revenue	$ 78,823	$ 66,188	$ 218,273	$ 189,155
Fee Revenue, Percentage	15.30%	13.90%	14.60%	13.20%
Education/Non-Profit
Disaggregation Of Revenue [Line Items]
Fee Revenue	$ 32,142	$ 29,108	$ 92,605	$ 90,748
Fee Revenue, Percentage	6.20%	6.10%	6.30%	6.30%
General
Disaggregation Of Revenue [Line Items]
Fee Revenue	$ 2,248	$ 3,338	$ 10,042	$ 11,967
Fee Revenue, Percentage	0.40%	0.80%	0.70%	0.80%
Fee Revenue
Disaggregation Of Revenue [Line Items]
Fee Revenue	$ 515,325	$ 474,504	$ 1,492,263	$ 1,435,277
Fee Revenue, Percentage	100.00%	100.00%	100.00%	100.00%