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, 2018	Apr. 30, 2017
Net income attributable to Butler National Corporation	$ 341	$ 1,534
Weighted average common shares outstanding (in shares)	64,387,694	63,455,883
Dilutive effect of non-qualified stock option plans (in shares)
Weighted average common shares outstanding, assuming dilution (in shares)	64,387,694	63,455,883
Potential common shares if all options were exercised and shares issued (in shares)	64,387,694	63,455,883
Basic earnings per common share (in dollars per share)	$ 0.01	$ 0.02
Diluted earnings per common share (in dollars per share)	$ 0.01	$ 0.02