Note 5 - Capital Stock and Transactions With Related Parties (Details Textual) - USD ($) $ / shares in Units, $ in Thousands					12 Months Ended			72 Months Ended
	Aug. 04, 2017	Jan. 27, 2017	Apr. 29, 2016	Jan. 25, 2013	Apr. 28, 2018	Apr. 29, 2017	Apr. 30, 2016	Apr. 28, 2018
Payments of Ordinary Dividends, Common Stock	$ 69,900	$ 69,900			$ 69,878	$ 69,850
Common Stock, Dividends, Per Share, Cash Paid	$ 1.50	$ 1.50
Stock Repurchase Program, Number of Shares Authorized to be Repurchased			1,600,000
Stock Repurchased During Period, Shares								502,060
Stock Repurchase Program, Remaining Number of Shares Authorized to be Repurchased					1,097,940			1,097,940
Increase (Decrease) in Shareholder Value					$ 4,800,000
Percentage Increase (Decrease) of Shareholder Value					11000.00%
CMA [Member]
Related Party Transaction, Amounts of Transaction					$ 9,800	8,300	$ 7,000
Accounts Payable, Total					2,400	$ 2,100		$ 2,400
Series D Preferred Stock [Member]
Stock Issued During Period, Shares, New Issues				400,000
Preferred Stock, Par or Stated Value Per Share				$ 1
Stock Issued During Period, Value, New Issues				$ 20,000
Stock Redeemed or Called During Period, Shares			120,000
Payments for Repurchase of Redeemable Preferred Stock			$ 6,000
Dividends Payable, Current					$ 0			$ 0
Series C Preferred Stock [Member]
Preferred Stock, Par or Stated Value Per Share					$ 1	$ 1		$ 1
Preferred Stock, Shares Issued, Total					150,000	150,000		150,000