Note G - Cash, Cash Equivalents And Marketable Securities (Details Textual) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 27, 2020	Sep. 29, 2019	Sep. 27, 2020	Sep. 29, 2019
Proceeds from Sale and Maturity of Debt Securities, Available-for-sale, Total	$ 23,224,000	$ 9,823,000	$ 41,859,000	$ 148,406,000
Debt Securities, Available-for-sale, Realized Gain (Loss), Total	0	0	0	0
OCI, Debt Securities, Available-for-Sale, Unrealized Holding Gain (Loss), before Adjustment and Tax	(81,000)	(28,000)	119,000	173,000
Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, Rolling within One Year, Fair Value	43,015,000		43,015,000
Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, Rolling after One Through Five Years, Fair Value	7,230,000		7,230,000
Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, Rolling after Five Through Ten Years, Fair Value	3,590,000		3,590,000
Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, Rolling after 10 Years, Fair Value	25,263,000		25,263,000
AOCI Attributable to Parent [Member]
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, before Tax, Total	$ 0	$ 0	$ 0	$ 0