Provision for Income Taxes - Components of Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Apr. 30, 2018	Apr. 30, 2017
Income Tax Disclosure [Abstract]
Accrued liabilities	$ 71	$ 103
Depreciation and amortization	(58)	0
State taxes	1	22
Stock-based compensation expense	4,466	6,503
Capitalized research and development costs	43	195
Foreign net operating loss carry-forward	208	214
Net operating loss carry-forward	9,678	14,786
Total deferred tax assets	14,409	21,823
Less: Valuation allowance	(14,409)	(21,779)
Net deferred tax asset	$ 0	$ 44