Note 1 - Nature of Operations, Organization and Significant Accounting Policies - Computation of Basic and Diluted Earnings Per Common Share (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Apr. 30, 2020	Apr. 30, 2019
Net income attributable to Butler National Corporation	$ 4,234	$ 3,853
Weighted average common shares outstanding (in shares)	68,622,527	64,511,608
Dilutive effect of non-qualified stock option plans (in shares)
Weighted average common shares outstanding, assuming dilution (in shares)	68,622,527	64,511,608
Potential common shares if all options were exercised and shares issued (in shares)	68,622,527	64,511,608
Basic earnings per common share (in dollars per share)	$ 0.06	$ 0.06
Diluted earnings per common share (in dollars per share)	$ 0.06	$ 0.06