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

9 Months Ended

Sep. 24, 2022

Notes Tables

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

	September 24, 2022
			Gross		Gross		Estimated
	Amortized		Unrealized		Unrealized		Fair
	Cost		Gains		Losses (1)		Value
Corporate debt securities (2)	$	72,632	$	6	$	371	$	72,267
U.S. treasury securities		32,522		-		422		32,100
Bank certificates of deposit		23,325		9		51		23,283
Foreign government security		783		-		-		783
Asset-backed securities		8,624		-		74		8,550
	$	137,886	$	15	$	918	$	136,983

	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

Investments Classified by Contractual Maturity Date [Table Text Block]

	September 24, 2022				December 25, 2021
	Amortized		Estimated		Amortized		Estimated
	Cost		Fair Value		Cost		Fair Value
Due in one year or less	$	112,027	$	111,625	$	83,429	$	83,408
Due after one year through three years		25,859		25,358		6,309		6,296
	$	137,886	$	136,983	$	89,738	$	89,704

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

	Fair value measurements at September 24, 2022 using:
							Total estimated
	Level 1		Level 2		Level 3		fair value
Cash	$	152,841	$	-	$	-	$	152,841
U.S. treasury securities		-		32,100		-		32,100
Corporate debt securities		-		80,744		-		80,744
Asset-backed securities		-		8,550		-		8,550
Money market funds		-		71,080		-		71,080
Bank certificates of deposit		-		23,283		-		23,283
Foreign government security		-		783		-		783
	$	152,841	$	216,540	$	-	$	369,381

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