Basic and Diluted Earnings Per Share (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended
	Jul. 31, 2014	Jul. 31, 2013
Earnings Per Share Disclosure [Line Items]
Net earnings attributable to common stockholders	$ 14,533	$ 11,417
Basic weighted-average number of common shares outstanding	48,703	47,665
Diluted weighted-average number of common shares outstanding	49,591	48,519
Basic earnings per share	$ 0.30	$ 0.24
Diluted earnings per share	$ 0.29	$ 0.24
Restricted Stock
Earnings Per Share Disclosure [Line Items]
Stock	756	659
Stock Options
Earnings Per Share Disclosure [Line Items]
Stock	132	195