Note 6 - Comprehensive Income - Components of Comprehensive Income (Details) - USD ($) $ in Thousands	3 Months Ended
	Jul. 31, 2018	Jul. 31, 2017
Change in unrealized gains (losses) on securities, amount before tax	$ 539	$ 142
Change in unrealized gains (losses) on securities, tax expense	(113)	(50)
Change in unrealized gains (losses) on securities, amount net of tax	426	92
Other comprehensive income (loss), available-for-sale securities adjustment, amount before tax	539	142
Other comprehensive income (loss), available-for-sale securities, tax expense	(113)	(50)
Other comprehensive income (loss), available-for-sale securities adjustment, amount net of tax	$ 426	$ 92