Computations of Net Loss Per Share Applicable to Common Stockholders (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended				9 Months Ended
	Jan. 31, 2014		Jan. 31, 2013		Jan. 31, 2014		Jan. 31, 2013
Schedule Of Computation Of Basic And Diluted Earnings Per Common Share [Line Items]
Net loss	$ (7,963)		$ (10,827)		$ (39,485)		$ (40,608)
Net loss per share, basic and diluted	$ (0.10)		$ (0.15)		$ (0.53)		$ (0.60)
Weighted average number of shares outstanding, basic and diluted	76,071		71,940		75,047		68,115
Potentially dilutive securities:
Outstanding stock options	1,761	[1]	4,435	[1]	2,520	[1]	6,786	[1]
Restricted shares	219	[1]			271	[1]

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