Provision for Income Taxes - Components of Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Apr. 30, 2017	Apr. 30, 2016
Income Tax Disclosure [Abstract]
Accrued liabilities	$ 103	$ 21
State taxes	22	12
Stock-based compensation expense	6,503	5,528
Capitalized research and development costs	195	316
Foreign net operating loss carry-forward	214	224
Net operating loss carry-forward	14,786	12,970
Total deferred tax assets	21,823	19,071
Less: Valuation allowance	(21,779)	(19,071)
Net deferred tax asset	$ 44	$ 0