Components of Stock-Based Compensation Expense Recognized (Detail) - USD ($) $ in Thousands	12 Months Ended
	Apr. 30, 2016	Apr. 30, 2015	Apr. 30, 2014
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total stock-based compensation expense, pre-tax	$ 18,895	$ 13,899	$ 12,106
Tax benefit from stock-based compensation expense	(7,347)	(3,893)	(3,484)
Total stock-based compensation expense, net of tax	11,548	10,006	8,622
Restricted Stock
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total stock-based compensation expense, pre-tax	18,288	13,602	11,689
Stock Options
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total stock-based compensation expense, pre-tax	17	135	$ 417
ESPP
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total stock-based compensation expense, pre-tax	$ 590	$ 162