Computations of Net Loss Per Share Applicable to Common Stockholders (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended
	Jul. 31, 2013		Jul. 31, 2012
Schedule Of Computation Of Basic And Diluted Earnings Per Common Share [Line Items]
Net loss	$ (17,368)		$ (18,539)
Net loss per share, basic and diluted	$ (0.23)		$ (0.30)
Weighted average number of shares outstanding, basic and diluted	73,983		62,451
Potentially dilutive securities:
Outstanding stock options	2,987	[1]	7,849	[1]
Restricted shares	188	[1]

[1] The impact of potentially dilutive securities on earnings per share is anti-dilutive in a period of net loss.