Note 11 - Comprehensive Income - Components of Comprehensive Income (Details) - USD ($) $ in Thousands	12 Months Ended
	Apr. 30, 2018	Apr. 30, 2017	Apr. 30, 2016
Change in unrealized gains (losses) on securities, amount before tax	$ 437	$ 554	$ 358
Change in unrealized gains (losses) on securities, tax expense	8	(196)	(126)
Change in unrealized gains (losses) on securities, amount net of tax	445	358	232
Less: Gains realized in net income, amount before tax	(152)	(39)	(329)
Less: Gains realized in net income, tax expense	32	14	117
Less: Gains realized in net income, amount net of tax	(120)	(25)	(212)
Other comprehensive income (loss), available-for-sale securities adjustment, amount before tax	285	515	29
Other comprehensive income (loss), available-for-sale securities, tax expense	40	(182)	(9)
Other comprehensive income (loss), available-for-sale securities adjustment, amount net of tax	$ 325	$ 333	$ 20