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, 2017	Apr. 30, 2016
Net income attributable to Butler National Corporation	$ 1,534	$ 24
Weighted average common shares outstanding (in shares)	63,455,883	62,263,404
Dilutive effect of non-qualified stock option plans (in shares)
Weighted average common shares outstanding, assuming dilution (in shares)	63,455,883	62,263,404
Potential common shares if all options were exercised and shares issued (in shares)	63,455,883	62,263,404
Basic earnings per common share (in dollars per share)	$ 0.02	$ 0
Diluted earnings per common share (in dollars per share)	$ 0.02	$ 0