Computations of Net Loss Per Share Applicable to Common Stockholders (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended				6 Months Ended
	Oct. 31, 2013		Oct. 31, 2012		Oct. 31, 2013		Oct. 31, 2012
Schedule Of Computation Of Basic And Diluted Earnings Per Common Share [Line Items]
Net loss	$ (14,154)		$ (11,242)		$ (31,522)		$ (29,781)
Net loss per share, basic and diluted	$ (0.19)		$ (0.16)		$ (0.42)		$ (0.45)
Weighted average number of shares outstanding, basic and diluted	75,088		69,846		74,535		66,203
Potentially dilutive securities:
Outstanding stock options	2,757	[1]	7,299	[1]	2,933	[1]	7,828	[1]
Restricted shares	351	[1]			270	[1]

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