Note 10 - 401(k) Savings Plan (Details Textual) - USD ($) $ in Thousands	12 Months Ended
	Apr. 30, 2019	Apr. 30, 2018
Number of Days of Service Eligible to Participate in Plan	30 days
Number of Entry Dates per Calendar Year to Participate in Plan	2
Defined Contribution Plan Matching Contribution, as Percent of Every Pretax Dollar	100.00%
Defined Contribution Plan, Employer Matching Contribution, Percent of Employees' Gross Pay	6.00%
Defined Contribution Plan, Employers Matching Contribution, Annual Vesting Percentage	100.00%
Defined Contribution Plan, Cost	$ 584	$ 261