Note 5 - Financial Instruments Measured at Fair Value - Short-term Investments by Security Type (Details) - USD ($) $ in Thousands		Dec. 31, 2016		Dec. 26, 2015
Amortized Cost		$ 31,995		$ 1,652
Gross Unrealized Gains		2
Gross Unrealized Losses		7	[1]
Short-term investments		31,990		1,652
Foreign Government Debt Securities [Member]
Amortized Cost		623		650
Gross Unrealized Gains
Gross Unrealized Losses			[1]
Short-term investments		623		650
Corporate Debt Securities [Member]
Amortized Cost	[2]	22,513
Gross Unrealized Gains	[2]	1
Gross Unrealized Losses	[1],[2]	6
Short-term investments	[2]	22,508
Certificates of Deposit [Member]
Amortized Cost		750		1,002
Gross Unrealized Gains		1
Gross Unrealized Losses			[1]
Short-term investments		751		$ 1,002
US Government-sponsored Enterprises Debt Securities [Member]
Amortized Cost		8,109
Gross Unrealized Gains
Gross Unrealized Losses	[1]	1
Short-term investments		$ 8,108

[1] 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.