Note 8 - Stock-based Compensation (Details Textual) - USD ($)	12 Months Ended
	Apr. 30, 2016	May 02, 2015	May 03, 2014
Omnibus Plan [Member] | Stock Options or Stock Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized	4,800,000
Omnibus Plan [Member] | SARS Dividend Equivalents and Other Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized	4,800,000
Omnibus Plan [Member]
Share Based Compensation Arrangement by Share Based Payment Award Number of Shares Authorized Per Individual	1,680,000
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period	5 years
Share-based Compensation Arrangement by Share-based Payment Award, Expiration Period	10 years
Special Stock Option Plan [Member] | Determined by Board of Directors [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized	1,800,000
Other Plan Member | Determined By Chairman Member
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized	50,000
KEEP Program [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized	240,000
Share Based Compensation Arrangement by Share Based Payment Award Number of Shares Authorized Per Individual	6,000
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period	6 years
Share Based Compensation Arrangement by Share Based Payment Award Percentage of Purchased Shares Matched	50.00%
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants, Period	2 years
Share-based Compensation Arrangement by Share-based Payment Award, Purchase Price of Common Stock, Percent	60.00%
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross	3,500	276,800	5,245
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Term	8 years	7 years 146 days	8 years
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Volatility Rate	29.00%	32.80%	35.80%
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Risk Free Interest Rate	2.10%	2.20%	1.90%
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Dividend Rate	3.30%	4.60%	4.60%
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Forfeiture Rate, Minimum	0.00%	0.00%	0.00%
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Forfeiture Rate, Maximum	16.00%	16.00%	16.00%
Allocated Share-based Compensation Expense	$ 228,000	$ 307,000	$ 95,000
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested in Period, Fair Value	652,000	371,000	90,000
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period, Intrinsic Value	5,161,000	917,000	76,000
Proceeds from Stock Options Exercised	848,000	228,000	47,000
Employee Service Share-based Compensation, Tax Benefit Realized from Exercise of Stock Options	$ 1,528,000	$ 240,000	$ 17,000
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Weighted Average Grant Date Fair Value	$ 20.09	$ 8.30	$ 12.50
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized	$ 642,000
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Period for Recognition	4 years 292 days
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Remaining Contractual Term	6 years 73 days
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested and Expected to Vest, Outstanding, Aggregate Intrinsic Value	$ 14,400,000
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Weighted Average Remaining Contractual Term	5 years
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested and Expected to Vest, Exercisable, Aggregate Intrinsic Value	$ 6,300,000
Employee Stock Ownership Plan (ESOP), Shares in ESOP	1,536,000