Note 3 - Financial Instruments Measured at Fair Value (Tables)

6 Months Ended

Jun. 30, 2018

Notes Tables

Available-for-sale Securities [Table Text Block]

	June 30, 2018
			Gross		Gross		Estimated
	Amortized		Unrealized		Unrealized		Fair
	Cost		Gains		Losses (1)		Value
Corporate debt securities (2)	$	10,849	$	1	$	5	$	10,845
U.S. Treasury securities		7,726		-		5		7,721
Bank certificates of deposit		3,750		-		-		3,750
Government-sponsored enterprise securities		994		-		1		993
Foreign government security		556		-		-		556
	$	23,875	$	1	$	11	$	23,865

	December 30, 2017
			Gross		Gross		Estimated
	Amortized		Unrealized		Unrealized		Fair
	Cost		Gains		Losses (1)		Value
Corporate debt securities (2)	$	12,784	$	1	$	6	$	12,779
U.S. treasury securities		7,935		-		4		7,931
Foreign government security		619		-		-		619
	$	21,338	$	1	$	10	$	21,329

Investments Classified by Contractual Maturity Date [Table Text Block]

	June 30, 2018				December 30, 2017
	Amortized		Estimated		Amortized		Estimated
	Cost		Fair Value		Cost		Fair Value
Due in one year or less	$	23,319	$	23,309	$	21,338	$	21,329
Due after one year through three years		556		556		-		-
	$	23,875	$	23,865	$	21,338	$	21,329

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

	Fair value measurements at June 30, 2018 using:
							Total estimated
	Level 1		Level 2		Level 3		fair value
Cash	$	99,422	$	-	$	-	$	99,422
U.S. Treasury securities		-		7,721		-		7,721
Corporate debt securities		-		19,178		-		19,178
Government-sponsored enterprise securities		-		994		-		994
Money market funds		-		19,253		-		19,253
Bank certificates of deposit		-		3,749		-		3,749
Foreign government security		-		556		-		556
	$	99,422	$	51,451	$	-	$	150,873

	Fair value measurements at December 30, 2017 using:
							Total estimated
	Level 1		Level 2		Level 3		fair value
Cash	$	100,850	$	-	$	-	$	100,850
Corporate debt securities		-		22,014		-		22,014
U.S. treasury securities		-		8,431		-		8,431
Government-sponsored enterprise securities		-		1,496		-		1,496
Money market funds		-		22,205		-		22,205
Foreign government security		-		619		-		619
	$	100,850	$	54,765	$	-	$	155,615