Provision for Income Taxes - Components of Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Apr. 30, 2016	Apr. 30, 2015
Income Tax Disclosure [Abstract]
Accrued liabilities	$ 21	$ 21
State taxes	12	1
Stock-based compensation expense	5,528	4,803
Capitalized research and development costs	316	433
Foreign net operating loss carry-forward	224	235
Net operating loss carry-forward	12,970	9,719
Total deferred tax assets	19,071	15,212
Less: Valuation allowance	(19,071)	(15,212)
Net deferred tax asset	$ 0	$ 0