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, 2017	Oct. 31, 2016	Oct. 31, 2017	Oct. 31, 2016
Schedule Of Computation Of Basic And Diluted Earnings Per Common Share [Line Items]
Net loss		$ (55)	$ (4,134)	$ (2,371)	$ (9,239)
Basic and diluted loss per share		$ 0.00	$ (0.05)	$ (0.03)	$ (0.11)
Basic and diluted weighted average number of shares outstanding		85,630	82,930	85,147	82,572
Outstanding stock options
Potentially dilutive securities (1):
Outstanding stock options	[1]	504	363	496	236
Restricted shares
Potentially dilutive securities (1):
Outstanding stock options	[1]	1,002	826	1,423	440

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