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								12 Months Ended
		Apr. 30, 2017	Jan. 31, 2017	Oct. 31, 2016	Jul. 31, 2016	Apr. 30, 2016	Jan. 31, 2016	Oct. 31, 2015	Jul. 31, 2015	Apr. 30, 2017	Apr. 30, 2016	Apr. 30, 2015
Schedule Of Computation Of Basic And Diluted Earnings Per Common Share [Line Items]
Net loss from continuing operations		$ (3,974)	$ (2,728)	$ (4,134)	$ (5,105)	$ (7,129)	$ (3,114)	$ (4,852)	$ (10,244)	$ (15,941)	$ (25,339)	$ (33,164)
Net loss from discontinued operations, net of tax										0	0	(1,257)
Net loss applicable to common stockholders										$ (15,941)	$ (25,339)	$ (34,421)
Continuing operations		$ (0.05)	$ (0.03)	$ (0.05)	$ (0.06)	$ (0.09)	$ (0.04)	$ (0.06)	$ (0.13)	$ (0.19)	$ (0.31)	$ (0.42)
Discontinued operations										0.00	0.00	(0.02)
Basic and diluted loss per share										$ (0.19)	$ (0.31)	$ (0.44)
Basic and diluted weighted average number of shares outstanding										83,051	80,859	78,645
Outstanding stock options
Potentially dilutive securities (1):
Outstanding stock options	[1]									390	197	721
Restricted shares
Potentially dilutive securities (1):
Outstanding stock options	[1]									857	49	427

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