Note 6 - Comprehensive Income - Components of Comprehensive Income (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Oct. 31, 2018	Oct. 31, 2017	Oct. 31, 2018	Oct. 31, 2017
Other comprehensive income (loss), available-for-sale securities adjustment, amount before tax			$ 229	$ 397
Other comprehensive income (loss), available-for-sale securities, tax expense			(48)	(140)
Other comprehensive income (loss), available-for-sale securities adjustment, amount net of tax	$ (245)	$ 165	181	257
Change in unrealized gains (losses) on securities, amount before tax			229	397
Change in unrealized gains (losses) on securities, tax expense			(48)	(140)
Change in unrealized gains (losses) on securities, amount net of tax			$ 181	$ 257