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

3 Months Ended

Mar. 27, 2021

Notes Tables

Available-for-sale Securities [Table Text Block]

	March 27, 2021
			Gross		Gross		Estimated
	Amortized		Unrealized		Unrealized		Fair
	Cost		Gains		Losses (1)		Value
Corporate debt securities (2)	$	136,400	$	16	$	11	$	136,405
U.S. Treasury securities		7,811		-		-		7,811
Government-sponsored enterprise securities		1,999		1		-		2,000
Bank certificates of deposit		750		-		-		750
Foreign government security		960		-		-		960
	$	147,920	$	17	$	11	$	147,926

	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]

	March 27, 2021				December 26, 2020
	Amortized		Estimated		Amortized		Estimated
	Cost		Fair Value		Cost		Fair Value
Due in one year or less	$	146,960	$	146,966	$	20,668	$	20,669
Due after one year through three years		960		960		-		-
	$	147,920	$	147,926	$	20,668	$	20,669

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

	Fair value measurements at March 27, 2021 using:
							Total estimated
	Level 1		Level 2		Level 3		fair value
Cash	$	115,626	$	-	$	-	$	115,626
U.S. Treasury securities		-		7,811		-		7,811
Corporate debt securities		-		136,405		-		136,405
Government-sponsored enterprise securities		-		2,000		-		2,000
Money market funds		-		27,493		-		27,493
Bank certificates of deposit		-		750		-		750
Foreign government security		-		960		-		960
	$	115,626	$	175,419	$	-	$	291,045

	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