Note 6 - Comprehensive Income - Components of Comprehensive Income (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		15 Months Ended
	Jan. 31, 2022	Jan. 31, 2021	Jan. 31, 2022	Jan. 31, 2021	Jan. 31, 2022
Change in unrealized losses on available-for-sale fixed income securities, amount before tax			$ (5)	$ (142)
Change in unrealized losses on available-for-sale fixed income securities, tax (expense) benefit			1	37
Change in unrealized losses on available-for-sale fixed income securities, amount net of tax			(4)	(105)
Other comprehensive income (loss), available-for-sale securities adjustment, amount before tax			(5)	(142)
Other comprehensive income (loss), available-for-sale securities, tax expense			1	37
Other comprehensive income (loss), available-for-sale securities adjustment, amount net of tax	$ 0	$ (59)	$ (4)	$ (105)	$ 0