Provision for Income Taxes - Narrative (Details) - USD ($) $ in Thousands	12 Months Ended
	Apr. 30, 2017	Apr. 30, 2016
Tax Credit Carryforward [Line Items]
Deferred tax assets, valuation allowance	$ 21,779	$ 19,071
Liabilities, other than long-term debt, noncurrent	121
Domestic Tax Authority
Tax Credit Carryforward [Line Items]
Operating loss carryforwards	$ 41,000	$ 36,000
Operating loss carryforwards, expiration year	2025
Foreign Tax Authority
Tax Credit Carryforward [Line Items]
Operating loss carryforwards	$ 900