Net Loss Per Share Applicable to Common Stockholders - Computations of Loss per Share Applicable to Common Stockholders (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands		3 Months Ended		6 Months Ended
		Oct. 31, 2016	Oct. 31, 2015	Oct. 31, 2016	Oct. 31, 2015
Schedule Of Computation Of Basic And Diluted Earnings Per Common Share [Line Items]
Net loss		$ (4,134)	$ (4,852)	$ (9,239)	$ (15,096)
Basic and diluted loss per share		$ (0.05)	$ (0.06)	$ (0.11)	$ (0.19)
Basic and diluted weighted average number of shares outstanding		82,930	80,678	82,572	80,426
Outstanding stock options
Potentially dilutive securities (1):
Outstanding stock options	[1]	363	212	236	266
Restricted shares
Potentially dilutive securities (1):
Outstanding stock options	[1]	826	11	440	38

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