Note 4 - Financial Instruments Measured at Fair Value - Short-term Investments by Security Type (Details) - USD ($) $ in Thousands		Dec. 30, 2017		Dec. 31, 2016
Amortized Cost		$ 21,338		$ 31,995
Gross Unrealized Gains		1		2
Gross Unrealized Losses		10	[1]	7
Short-term investments		21,329		31,990
Corporate Debt Securities [Member]
Amortized Cost	[2]	12,784		22,513
Gross Unrealized Gains	[2]	1		1
Gross Unrealized Losses	[2]	6	[1]	6
Short-term investments	[2]	12,779		22,508
Foreign Government Debt Securities [Member]
Amortized Cost		619		623
Gross Unrealized Gains
Gross Unrealized Losses			[1]
Short-term investments		619		623
US Treasury Securities [Member]
Amortized Cost		7,935
Gross Unrealized Gains
Gross Unrealized Losses	[1]	4
Short-term investments		$ 7,931
US Government-sponsored Enterprises Debt Securities [Member]
Amortized Cost				8,109
Gross Unrealized Gains
Gross Unrealized Losses				1
Short-term investments				8,108
Certificates of Deposit [Member]
Amortized Cost				750
Gross Unrealized Gains				1
Gross Unrealized Losses
Short-term investments				$ 751

[1] As of December 30, 2017, the cost and fair value of investments with loss positions were approximately $13.2 million. As of December 31, 2016, the cost and fair value of investments with loss positions were approximately $26.6 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] 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.