Loss Per Share Applicable to Common Stockholders (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended
	Jul. 31, 2012	Jul. 31, 2011
Earnings Per Share, Basic and Diluted
Net loss	$ (18,539)	$ (5,536)
Less accretion of redeemable convertible preferred stock		(13)
Loss applicable to common stockholders	$ (18,539)	$ (5,549)
Basic and diluted earnings per share	$ 0.30	$ (0.29)
Weighted average number of shares	62,451	18,817
Potentially dilutive securities (1):
Outstanding stock options	7,849	4,575
Redeemable convertible preferred shares		27,897