Fee Revenue - Schedule of Disaggregation of Fee Revenue by Industry (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Jan. 31, 2019	Jan. 31, 2018	Jan. 31, 2019	Jan. 31, 2018
Disaggregation Of Revenue [Line Items]
Fee Revenue	$ 486,172	$ 460,770	$ 1,471,327	$ 1,331,155
Industrial
Disaggregation Of Revenue [Line Items]
Fee Revenue	$ 137,436	$ 134,512	$ 419,559	$ 388,607
Fee Revenue, Percentage	29.00%	30.10%	29.20%	30.10%
Financial Services
Disaggregation Of Revenue [Line Items]
Fee Revenue	$ 86,397	$ 74,044	$ 259,962	$ 224,771
Fee Revenue, Percentage	18.20%	16.60%	18.10%	17.40%
Life Sciences/ Healthcare
Disaggregation Of Revenue [Line Items]
Fee Revenue	$ 76,066	$ 76,237	$ 239,891	$ 214,771
Fee Revenue, Percentage	16.00%	17.00%	16.70%	16.60%
Consumer Goods
Disaggregation Of Revenue [Line Items]
Fee Revenue	$ 74,007	$ 72,229	$ 226,159	$ 204,323
Fee Revenue, Percentage	15.60%	16.10%	15.80%	15.80%
Technology
Disaggregation Of Revenue [Line Items]
Fee Revenue	$ 64,248	$ 57,823	$ 188,088	$ 165,893
Fee Revenue, Percentage	13.60%	12.90%	13.10%	12.80%
Education/Non-Profit
Disaggregation Of Revenue [Line Items]
Fee Revenue	$ 29,083	$ 30,019	$ 91,250	$ 84,538
Fee Revenue, Percentage	6.10%	6.70%	6.40%	6.60%
General
Disaggregation Of Revenue [Line Items]
Fee Revenue	$ 7,267	$ 2,717	$ 10,368	$ 8,950
Fee Revenue, Percentage	1.50%	0.60%	0.70%	0.70%
Fee Revenue
Disaggregation Of Revenue [Line Items]
Fee Revenue	$ 474,504	$ 447,581	$ 1,435,277	$ 1,291,853
Fee Revenue, Percentage	100.00%	100.00%	100.00%	100.00%