Fee Revenue - Schedule of Disaggregation of Fee Revenue by Industry (Detail) - USD ($) $ in Thousands	3 Months Ended
	Jul. 31, 2018	Jul. 31, 2017
Disaggregation Of Revenue [Line Items]
Fee Revenue	$ 478,362	$ 414,917
Industrial
Disaggregation Of Revenue [Line Items]
Fee Revenue	$ 135,764	$ 121,447
Fee Revenue, Percentage	29.20%	30.30%
Financial Services
Disaggregation Of Revenue [Line Items]
Fee Revenue	$ 80,193	$ 67,260
Fee Revenue, Percentage	17.20%	16.80%
Life Sciences/Healthcare
Disaggregation Of Revenue [Line Items]
Fee Revenue	$ 79,169	$ 66,580
Fee Revenue, Percentage	17.00%	16.60%
Consumer Goods
Disaggregation Of Revenue [Line Items]
Fee Revenue	$ 71,794	$ 61,831
Fee Revenue, Percentage	15.40%	15.40%
Technology
Disaggregation Of Revenue [Line Items]
Fee Revenue	$ 61,849	$ 51,772
Fee Revenue, Percentage	13.30%	12.90%
Education
Disaggregation Of Revenue [Line Items]
Fee Revenue	$ 32,936	$ 28,677
Fee Revenue, Percentage	7.10%	7.10%
General
Disaggregation Of Revenue [Line Items]
Fee Revenue	$ 3,863	$ 3,687
Fee Revenue, Percentage	0.80%	0.90%
Fee Revenue
Disaggregation Of Revenue [Line Items]
Fee Revenue	$ 465,568	$ 401,254
Fee Revenue, Percentage	100.00%	100.00%