Components of Stock-Based Compensation Expense Recognized (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Jan. 31, 2017	Jan. 31, 2016	Jan. 31, 2017	Jan. 31, 2016
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total stock-based compensation expense, pre-tax	$ 4,581	$ 4,526	$ 14,101	$ 13,539
Tax benefit from stock-based compensation expense	(1,111)	(1,989)	(3,778)	(4,857)
Total stock-based compensation expense, net of tax	3,470	2,537	10,323	8,682
Restricted Stock
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total stock-based compensation expense, pre-tax	4,406	4,399	13,497	13,131
Stock Options
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total stock-based compensation expense, pre-tax				17
ESPP
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total stock-based compensation expense, pre-tax	$ 175	$ 127	$ 604	$ 391