Basic and Diluted Earnings Per Share (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended	6 Months Ended
Oct. 31, 2014	Oct. 31, 2013	Oct. 31, 2014	Oct. 31, 2013
Earnings Per Share Disclosure [Line Items]
Net earnings attributable to common stockholders	$ 25,403	$ 18,759	$ 39,936	$ 30,176
Basic weighted-average number of common shares outstanding	49,082	48,118	48,893	47,892
Diluted weighted-average number of common shares outstanding	49,740	48,816	49,720	48,748
Basic earnings per share	$ 0.52	$ 0.39	$ 0.82	$ 0.63
Diluted earnings per share	$ 0.51	$ 0.38	$ 0.80	$ 0.62
Restricted Stock
Earnings Per Share Disclosure [Line Items]
Stock	554	484	710	643
Stock Options
Earnings Per Share Disclosure [Line Items]
Stock	104	214	117	213

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The amount of net income (loss) for the period per each share of common stock or unit outstanding during the reporting period.

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The amount of net income (loss) for the period available to each share of common stock or common unit outstanding during the reporting period and to each share or unit that would have been outstanding assuming the issuance of common shares or units for all dilutive potential common shares or units outstanding during the reporting period.

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Additional shares included in the calculation of diluted EPS as a result of the potentially dilutive effect of share based payment arrangements using the treasury stock method.

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The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

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