Note 9 - Stock-based Compensation - Summary of Stock Option Activity (Details) - $ / shares		12 Months Ended
		Apr. 27, 2019	Apr. 28, 2018	Apr. 29, 2017
Options outstanding, beginning of year (in shares)		344,945
Options outstanding, beginning of year (in dollars per share)	[1]	$ 10.84
Granted (in shares)		9,000	500	0
Granted (in dollars per share)	[1]	$ 40.03
Exercised (in shares)		(27,300)
Exercised (in dollars per share)	[1]	$ 16.70
Cancelled (in shares)		(4,200)
Cancelled (in dollars per share)	[1]	$ 14.17
Options outstanding, end of year (in shares)		322,445	344,945
Options outstanding, end of year (in dollars per share)	[1]	$ 11.14	$ 10.84
Options exercisable, end of year (in shares)		230,259
Options exercisable, end of year (in dollars per share)	[1]	$ 9.16

[1] Weighted average exercise price.