Note 11 - Treasury Stock and Repurchase Program - Treasury Stock at Cost (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Oct. 31, 2021	Jul. 31, 2021	Oct. 31, 2021	Oct. 31, 2020	Apr. 30, 2021
Balance, shares (in shares)		436,830	436,830
Balance, total average cost assigned		$ 7,483	$ 7,483
Balance, average cost per share (in dollars per share)		$ 17.13	$ 17.13
Balance, aggregate purchase price remaining under the program	$ 1,646	$ 2,000	$ 1,646		$ 474
Purchases effected in open market, shares (in shares)	11,180	5,409
Purchases effected in open market, cost	$ 354	$ 163	$ 517	$ 422
Purchases effected in open market, average cost (in dollars per share)	$ 31.67	$ 30.13
Balance, shares (in shares)	453,419		453,419
Balance, total average cost assigned	$ 8,000		$ 8,000
Balance, average cost per share (in dollars per share)	$ 17.64		$ 17.64