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

12 Months Ended

Dec. 31, 2016

Notes Tables

Available-for-sale Securities [Table Text Block]

	At December 31, 2016
			Gross		Gross		Estimated
	Amortized		Unrealized		Unrealized		Fair
	Cost		Gains		Losses (1)		Value
Foreign government security	$	623	$	-	$	-	$	623
Corporate debt securities (2)		22,513		1		6		22,508
Government-sponsored  enterprise securities		8,109		-		1		8,108
Bank certificates of deposit		750		1		-		751
	$	31,995	$	2	$	7	$	31,990

	At December 26, 2015
			Gross		Gross		Estimated
	Amortized		Unrealized		Unrealized		Fair
	Cost		Gains		Losses		Value
Foreign government security	$	650	$	-	$	-	$	650
Bank certificates of deposit		1,002		-		-		1,002
	$	1,652	$	-	$	-	$	1,652

Investments Classified by Contractual Maturity Date [Table Text Block]

	Amortized		Estimated
(in thousands)	Cost		Fair Value
Due in one year or less	$	31,372	$	31,367
Due after one year through three years		623		623
	$	31,995	$	31,990

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

	Fair value measurements at December 31, 2016 using:
							Total estimated
	Level 1		Level 2		Level 3		fair value
Cash	$	70,279	$	-	$	-	$	70,279
Foreign government security		-		623		-		623
Corporate debt securities		-		24,108		-		24,108
Government-sponsored enterprise securities		-		8,108		-		8,108
Money market funds		-		24,166		-		24,166
Bank certificates of deposit		-		751		-		751
	$	70,279	$	57,756	$	-	$	128,035

	Fair value measurements at December 26, 2015 using:
							Total estimated
	Level 1		Level 2		Level 3		fair value
Cash	$	73,746	$	-	$	-	$	73,746
Foreign government security		-		650		-		650
Money market funds		-		41,624		-		41,624
Bank certificates of deposit		-		1,002		-		1,002
	$	73,746	$	43,276	$	-	$	117,022