Note 6 - Comprehensive Income - Components of Comprehensive Income (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Oct. 31, 2019	Oct. 31, 2018	Oct. 31, 2019	Oct. 31, 2018
Change in unrealized gains (losses) on securities, amount before tax			$ 457	$ 229
Change in unrealized gains (losses) on securities, tax expense			(95)	(48)
Change in unrealized gains (losses) on securities, amount net of tax			362	181
Other comprehensive income (loss), available-for-sale securities adjustment, amount before tax			457	229
Other comprehensive income (loss), available-for-sale securities, tax expense			(95)	(48)
Other comprehensive income (loss), available-for-sale securities adjustment, amount net of tax	$ 276	$ (245)	$ 362	$ 181