Note 3 - Financial Instruments Measured at Fair Value - Short-term Investments by Security Type (Details) - USD ($) $ in Thousands		Mar. 31, 2018	Dec. 30, 2017
Amortized Cost		$ 24,612	$ 21,338
Gross Unrealized Gains			1
Gross Unrealized Losses	[1]	18	10
Short-term investments		24,594	21,329	[2]
Corporate Debt Securities [Member]
Amortized Cost	[3]	11,313	12,784
Gross Unrealized Gains	[3]		1
Gross Unrealized Losses	[1],[3]	9	6
Short-term investments	[3]	11,304	12,779
US Treasury Securities [Member]
Amortized Cost		8,913	7,935
Gross Unrealized Gains
Gross Unrealized Losses	[1]	8	4
Short-term investments		8,905	7,931
Certificates of Deposit [Member]
Amortized Cost		2,800
Gross Unrealized Gains
Gross Unrealized Losses	[1]	1
Short-term investments		2,799
Debt Security, Government, Non-US [Member]
Amortized Cost		594	619
Gross Unrealized Gains
Gross Unrealized Losses	[1]
Short-term investments		594	$ 619
US Government-sponsored Enterprises Debt Securities [Member]
Amortized Cost		992
Gross Unrealized Gains
Gross Unrealized Losses	[1]
Short-term investments		$ 992

[1] As of March 31, 2018, there were $23.5 million of investments in our portfolio in a loss position. As of December 30, 2017, the cost and fair value of investments with loss positions were approximately $13.2 million. We evaluated the nature of these investments, credit worthiness of the issuer and the duration of these impairments to determine if an other-than-temporary decline in fair value had occurred and concluded that these losses were temporary and we have the ability and intent to hold these investments to maturity.

[2] Derived from December 30, 2017 audited financial statements

[3] Corporate debt securities include investments in financial and other corporate institutions. No single issuer represents a significant portion of the total corporate debt securities portfolio.