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
		Jul. 31, 2016	Jul. 31, 2015
Schedule Of Computation Of Basic And Diluted Earnings Per Common Share [Line Items]
Net loss		$ (5,105)	$ (10,244)
Basic and diluted loss per share		$ (0.06)	$ (0.13)
Basic and diluted weighted average number of shares outstanding		82,214	80,174
Outstanding stock options
Potentially dilutive securities (1):
Outstanding stock options	[1]	132	324
Restricted shares
Potentially dilutive securities (1):
Outstanding stock options	[1]	47	58

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