Note 5 - Financial Instruments Measured at Fair Value (Tables)

9 Months Ended

Sep. 25, 2021

Notes Tables

Unrealized Gain (Loss) on Investments [Table Text Block]

	September 25, 2021
			Gross		Gross		Estimated
	Amortized		Unrealized		Unrealized		Fair
	Cost		Gains		Losses (1)		Value
Corporate debt securities (2)	$	68,333	$	10	$	3	$	68,340
U.S. Treasury securities		3,216		-		-		3,216
Government-sponsored enterprise securities		2,000		-		-		2,000
Bank certificates of deposit		1,550		1		-		1,551
Foreign government security		913		-		-		913
	$	76,012	$	11	$	3	$	76,020

			December 26, 2020
			Gross		Gross		Estimated
	Amortized		Unrealized		Unrealized		Fair
	Cost		Gains		Losses (1)		Value
Corporate debt securities (2)	$	14,943	$	2	$	1	$	14,944
U.S. treasury securities		2,012		-		-		2,012
Government-sponsored enterprise securities		1,998		-		-		1,998
Bank certificates of deposit		750		-		-		750
Foreign government security		965		-		-		965
	$	20,668	$	2	$	1	$	20,669

Investments Classified by Contractual Maturity Date [Table Text Block]

	September 25, 2021				December 26, 2020
	Amortized		Estimated		Amortized		Estimated
	Cost		Fair Value		Cost		Fair Value
Due in one year or less	$	73,545	$	73,553	$	20,668	$	20,669
Due after one year through three years		2,467		2,467		-		-
	$	76,012	$	76,020	$	20,668	$	20,669

Fair Value, Assets Measured on Recurring Basis [Table Text Block]

	Fair value measurements at September 25, 2021 using:
							Total estimated
	Level 1		Level 2		Level 3		fair value
Cash	$	236,946	$	-	$	-	$	236,946
U.S. Treasury securities		-		3,216		-		3,216
Corporate debt securities		-		72,430		-		72,430
Government-sponsored enterprise securities		-		2,000		-		2,000
Money market funds		-		47,750		-		47,750
Bank certificates of deposit		-		1,551		-		1,551
Foreign government security		-		912		-		912
	$	236,946	$	127,859	$	-	$	364,805

	Fair value measurements at December 26, 2020 using:
							Total estimated
	Level 1		Level 2		Level 3		fair value
Cash	$	128,874	$	-	$	-	$	128,874
Corporate debt securities		-		15,694		-		15,694
U.S. treasury securities		-		2,012		-		2,012
Government-sponsored enterprise securities		-		1,998		-		1,998
Money market funds		-		19,734		-		19,734
Bank certificates of deposit		-		750		-		750
Foreign government security		-		965		-		965
	$	128,874	$	41,153	$	-	$	170,027