Note N - Stockholders' Equity (Details Textual) - USD ($)			3 Months Ended		116 Months Ended	213 Months Ended
	Aug. 09, 2019	Jun. 14, 2019	Jun. 30, 2019	Jun. 24, 2018	Jun. 30, 2019	Jun. 30, 2019	Mar. 11, 2016
Common Stock, Dividends, Per Share, Declared		$ 0.35	$ 0.35	$ 0.25
Payments of Ordinary Dividends, Common Stock		$ 1,479,000
Treasury Stock, Shares, Acquired			0			5,141,763
Treasury Stock, Value, Acquired, Cost Method						$ 78,303,000
Sixth Stock Repurchase Plan [Member]
Treasury Stock, Shares, Acquired					954,132
Treasury Stock, Value, Acquired, Cost Method					$ 30,641,000
Stock Repurchase Program, Number of Shares Authorized to be Repurchased							1,200,000
Stock Repurchase Program, Remaining Number of Shares Authorized to be Repurchased			245,868		245,868	245,868
Subsequent Event [Member]
Common Stock, Dividends, Per Share, Declared	$ 0.35