Computations of Loss Per Share Applicable to Common Stockholders (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Apr. 30, 2013	Jan. 31, 2013	Oct. 31, 2012	Jul. 31, 2012	Apr. 30, 2012	Jan. 31, 2012	Oct. 31, 2011	Jul. 31, 2011	Apr. 30, 2013		Apr. 30, 2012		Apr. 30, 2011
Schedule Of Computation Of Basic And Diluted Earnings Per Common Share [Line Items]
Net loss	$ (23,144)	$ (10,827)	$ (11,242)	$ (18,539)	$ (6,367)	$ (6,575)	$ (5,851)	$ (5,536)	$ (63,752)		$ (24,329)		$ (20,057)
Less accretion of redeemable convertible preferred stock											(38)		(46)
Net loss applicable to common stockholders									$ (63,752)		$ (24,367)		$ (20,103)
Net loss per share applicable to common stockholders, basic and diluted	$ (0.32)	$ (0.15)	$ (0.16)	$ (0.30)	$ (0.13)	$ (0.34)	$ (0.30)	$ (0.29)	$ (0.92)		$ (0.92)		$ (1.13)
Weighted average number of shares outstanding, basic and diluted									69,336		26,403		17,790
Potentially dilutive securities:
Outstanding stock options									5,718	[1]	6,241	[1]	3,941	[1]
Redeemable convertible preferred shares											22,714	[1]	27,897	[1]
Restricted shares									67	[1]	1	[1]

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