Note 5 - Capital Stock and Transactions With Related Parties (Details Textual) - USD ($)							12 Months Ended					16 Months Ended	24 Months Ended	60 Months Ended
	May 05, 2017	Jan. 27, 2017	Apr. 29, 2016	Aug. 01, 2014	May 02, 2014	Jan. 25, 2013	Apr. 29, 2017	Apr. 30, 2016	Apr. 30, 2016	May 02, 2015	Apr. 30, 2015	Apr. 30, 2014	Apr. 29, 2017	Apr. 29, 2017	May 01, 2014
Stock Redeemed or Called During Period, Shares			120,000
Payments for Repurchase of Redeemable Preferred Stock			$ 6,000,000
Preferred Stock, Accretion of Redemption Discount			$ 89,000
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	1,097,940
Increase (Decrease) in Shareholder Value							$ 4,500,000,000
Percentage Increase (Decrease) of Shareholder Value							10000.00%
Payments of Ordinary Dividends, Common Stock		$ 69,900,000					$ 69,850,000
Common Stock, Dividends, Per Share, Cash Paid		$ 1.50
CMA [Member]
Related Party Transaction, Amounts of Transaction							8,300,000		7,000,000	$ 6,500,000
Accounts Payable							2,100,000	$ 1,800,000	1,800,000				$ 2,100,000	$ 2,100,000
Series D Preferred Stock [Member]
Stock Redeemed or Called During Period Percentage					40.00%
Stock Redeemed or Called During Period, Value					$ 8,000,000
Issuance Cost Related to Stock Redeemed					$ 118,000
Preferred Stock, Dividend Rate, Percentage								2.50%			2.50%	3.00%
Stock Redeemed or Called During Period, Shares				120,000	160,000
Stock Redeemed in Period, Percentage				50.00%
Payments for Repurchase of Redeemable Preferred Stock				$ 6,000,000
Preferred Stock, Accretion of Redemption Discount				$ 89,000
Preferred Stock Dividend Rate Basis Spread On Variable Rate													3.70%
Dividends Payable, Current							$ 0	$ 0	$ 0				$ 0	$ 0
Preferred Stock, Redemption Price Per Share															$ 50
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						$ 20,000,000
Temporary Equity, Liquidation Preference Per Share						$ 50
Series C Preferred Stock [Member]
Preferred Stock, Shares Issued							150,000	150,000	150,000				150,000	150,000
Preferred Stock, Par or Stated Value Per Share							$ 1	$ 1	$ 1				$ 1	$ 1
Subsequent Event [Member]
Common Stock, Dividends, Per Share, Declared	$ 1.50
Subsequent Event [Member] | Common Stock [Member]
Dividends Payable, Date of Record	Jun. 05, 2017
Dividends Payable, Date to be Paid	Aug. 04, 2017
Dividends Payable	$ 69,900,000