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

6 Months Ended

Jun. 26, 2021

Notes Tables

Available-for-sale Securities [Table Text Block]

	June 26, 2021
			Gross		Gross		Estimated
	Amortized		Unrealized		Unrealized		Fair
	Cost		Gains		Losses (1)		Value
Corporate debt securities (2)	$	70,707	$	15	$	1	$	70,721
U.S. Treasury securities		4,967		-		-		4,967
Government-sponsored enterprise securities		2,000		-		-		2,000
Bank certificates of deposit		1,550		1		-		1,551
Foreign government security		954		-		-		954
	$	80,178	$	16	$	1	$	80,193

	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]

	June 26, 2021				December 26, 2020
	Amortized		Estimated		Amortized		Estimated
	Cost		Fair Value		Cost		Fair Value
Due in one year or less	$	79,224	$	79,239	$	20,668	$	20,669
Due after one year through three years		954		954		-		-
	$	80,178	$	80,193	$	20,668	$	20,669

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

	Fair value measurements at June 26, 2021 using:
							Total estimated
	Level 1		Level 2		Level 3		fair value
Cash	$	346,197	$	-	$	-	$	346,197
U.S. Treasury securities		-		4,967		-		4,967
Corporate debt securities		-		70,721		-		70,721
Government-sponsored enterprise securities		-		2,000		-		2,000
Money market funds		-		7,699		-		7,699
Bank certificates of deposit		-		1,551		-		1,551
Foreign government security		-		954		-		954
	$	346,197	$	87,892	$	-	$	434,089

	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