Note 6 - Comprehensive Income - Components of Comprehensive Income (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Jan. 31, 2020	Jan. 31, 2019	Jan. 31, 2020	Jan. 31, 2019
Change in unrealized gains (losses) on securities, amount before tax			$ 592	$ 438
Change in unrealized gains (losses) on securities, tax expense			(260)	(93)
Change in unrealized gains (losses) on securities, amount net of tax			332	345
Other comprehensive income (loss), available-for-sale securities adjustment, amount before tax			592	438
Other comprehensive income (loss), available-for-sale securities, tax expense			(260)	(93)
Other comprehensive income (loss), available-for-sale securities adjustment, amount net of tax	$ (30)	$ 164	$ 332	$ 345