Stockholders' Equity - Reconciliation of Net Income Amounts and Weighted Average Number of Common and Common Equivalent Shares Used to Determine Basic and Diluted Earnings per Share (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended
	Jul. 31, 2016	Jul. 31, 2015
Earnings Per Share [Abstract]
Net income	$ 32,616	$ 14,412
Basic earnings, Shares	56,049	54,218
Effect of dilutive stock awards, Shares	834	1,259
Diluted earnings, Shares	56,883	55,477
Basic earnings, Per Share Amount	$ 0.58	$ 0.27
Effect of dilutive stock awards, Per Share Amount	(0.01)	(0.01)
Diluted earnings, Per Share Amount	$ 0.57	$ 0.26