Note 7 - Employee Stock Plans (Details Textual) - shares	Mar. 05, 2020	Apr. 26, 2017	Apr. 23, 2015	Apr. 04, 2021	Apr. 24, 2019
Stock Plan 2019 [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant (in shares)				538,000	357,143
Share-based Compensation Arrangement by Share-based Payment Award, Number of Additional Shares Authorized (in shares)	550,000
Stock Plan 2009 [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant (in shares)					299,070
The 2009 Employee Stock Purchase Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant (in shares)				341,926
Share-based Compensation Arrangement by Share-based Payment Award, Number of Additional Shares Authorized (in shares)	300,000	107,143	71,429