Note 11 - Quarterly Financial Data (Unaudited) - Summary of Quarterly Financial Data (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Apr. 28, 2018	Jan. 27, 2018	Oct. 28, 2017	Jul. 29, 2017	Apr. 29, 2017	Jan. 28, 2017	Oct. 29, 2016	Jul. 30, 2016	Apr. 28, 2018	Apr. 29, 2017	Apr. 30, 2016
Net sales	$ 244,306	$ 227,477	$ 244,119	$ 259,832	$ 212,066	$ 194,564	$ 203,180	$ 217,108	$ 975,734	$ 826,918	$ 704,785
Gross profit	99,359	91,193	96,080	104,503	85,946	75,920	78,717	85,494	391,135	326,077	241,437
Net income	$ 36,442	$ 41,080	$ 33,980	$ 38,272	$ 29,161	$ 24,285	$ 24,604	$ 28,995	$ 149,774	$ 107,045	$ 61,198
Earnings per common share – basic (in dollars per share)	$ 0.78	$ 0.88	$ 0.73	$ 0.82	$ 0.63	$ 0.52	$ 0.53	$ 0.62	$ 3.21	$ 2.30	$ 1.31
Earnings per common share – diluted (in dollars per share)	0.78	0.88	0.72	0.82	0.62	0.52	0.53	0.62	3.19	2.29	1.31
Earnings per common share – basic (in dollars per share)	0.78	0.88	0.73	0.82	0.63	0.52	0.53	0.62	3.21	2.30	1.31
Earnings per common share – diluted (in dollars per share)	$ 0.78	$ 0.88	$ 0.72	$ 0.82	$ 0.62	$ 0.52	$ 0.53	$ 0.62	$ 3.19	$ 2.29	$ 1.31