Basic and Diluted Earnings Per Share (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Jan. 31, 2013	Jan. 31, 2012	Jan. 31, 2013	Jan. 31, 2012
Earnings Per Share Disclosure [Line Items]
Net earnings attributable to common stockholders	$ 9,482	$ 11,717	$ 21,096	$ 42,275
Basic weighted-average number of common shares outstanding	47,367	46,528	47,149	46,332
Restricted stock	491	567	426	567
Stock options	157	250	167	279
ESPP				15
Diluted weighted-average number of common shares outstanding	48,015	47,345	47,742	47,193
Basic earnings per share	$ 0.20	$ 0.25	$ 0.45	$ 0.91
Diluted earnings per share	$ 0.20	$ 0.25	$ 0.44	$ 0.90