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

12 Months Ended

Dec. 25, 2021

Notes Tables

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

	At December 25, 2021
			Gross		Gross		Estimated
	Amortized		Unrealized		Unrealized		Fair
	Cost		Gains		Losses (1)		Value
Corporate debt securities (2)	$	84,060	$	2	$	31	$	84,031
U.S. treasury securities		3,953		-		5		3,948
Bank certificates of deposit		800		-		-		800
Foreign government security		925		-		-		925
	$	89,738	$	2	$	36	$	89,704

	At 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]

	Amortized		Estimated
(in thousands)	Cost		Fair Value
Due in one year or less	$	83,429	$	83,408
Due after one year through three years		6,309		6,296
	$	89,738	$	89,704

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

	Fair value measurements at December 25, 2021 using:
							Total estimated
	Level 1		Level 2		Level 3		fair value
Cash	$	195,297	$	-	$	-	$	195,297
Money market funds		-		92,400		-		92,400
Foreign government security		-		925		-		925
Corporate debt securities		-		86,535		-		86,535
U.S. treasury securities		-		3,948		-		3,948
Bank certificates of deposit		-		800		-		800
	$	195,297	$	184,608	$	-	$	379,905

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