Note 11 - Treasury Stock and Repurchase Program - Treasury Stock at Cost (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended				9 Months Ended
	Jan. 31, 2022	Oct. 31, 2021	Jul. 31, 2021	Jan. 31, 2021	Jan. 31, 2022	Jan. 31, 2021	Mar. 14, 2022
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	$ 474		$ 474
Purchases effected in open market, shares (in shares)	17,418	11,180	5,409
Purchases effected in open market, cost	$ 805	$ 354	$ 163	$ 623	1,322	$ 1,045
Purchases effected in open market, average cost (in dollars per share)	$ 46.21	$ 31.67	$ 30.13
Balance, aggregate purchase price remaining under the program	$ 841	$ 1,646	$ 2,000		841
January 31, 2022	$ 841	1,646	2,000		$ 841
Balance, shares (in shares)	470,837				470,837
Balance, total average cost assigned	$ 8,805				$ 8,805
Balance, average cost per share (in dollars per share)	$ 18.70				$ 18.70
Balance, aggregate purchase price remaining under the program	$ 841	$ 1,646	$ 2,000		$ 841
Authorized as of March 14, 2022							$ 2,000