Income Taxes - Schedule of Income Tax Reconciliation (Detail) - USD ($)	12 Months Ended
	Apr. 30, 2018	Apr. 30, 2017	Apr. 30, 2016
Income Tax Disclosure [Abstract]
Income tax expense at statutory rate	$ 2,818,000	$ 2,294,000	$ 1,952,000
State and local taxes, net of federal income tax benefit (expense)	162,000	100,000	102,000
Tax credits (state, net of federal benefit)	(370,000)	(110,000)	(407,000)
Effects of differing US and foreign tax rates	(97,000)	(7,000)	173,000
Rate reduction impact on deferred tax assets	680,000
Federal and state transition tax on unrepatriated foreign earnings	649,000
Increase (decrease) in valuation allowance	175,000	82,000	(10,000)
Other items, net	98,000	(233,000)	52,000
Net income tax expense	$ 4,115,000	$ 2,126,000	$ 1,862,000