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, 2019	Apr. 30, 2018
Net income attributable to Butler National Corporation	$ 3,853	$ 341
Weighted average common shares outstanding (in shares)	64,511,608	64,387,694
Dilutive effect of non-qualified stock option plans (in shares)
Weighted average common shares outstanding, assuming dilution (in shares)	64,511,608	64,387,694
Potential common shares if all options were exercised and shares issued (in shares)	64,511,608	64,387,694
Basic earnings per common share (in dollars per share)	$ 0.06	$ 0.01
Diluted earnings per common share (in dollars per share)	$ 0.06	$ 0.01