Note 4 - Financial Instruments Measured at Fair Value - Short-term Investments by Security Type (Details) - USD ($) $ in Thousands		Sep. 24, 2016	Dec. 26, 2015
Corporate Debt Securities [Member]
Amortized Cost	[1]	$ 11,489
Gross Unrealized Gains	[1]
Gross Unrealized Losses	[1]	5
Short-term investments	[1]	11,484
Foreign Government Debt Securities [Member]
Amortized Cost		639	$ 650
Gross Unrealized Gains
Gross Unrealized Losses
Short-term investments		639	650
Certificates of Deposit [Member]
Amortized Cost		3,313	1,002
Gross Unrealized Gains		1
Gross Unrealized Losses
Short-term investments		3,314	1,002
US Government-sponsored Enterprises Debt Securities [Member]
Amortized Cost		4,012
Gross Unrealized Gains		2
Gross Unrealized Losses
Short-term investments		4,014
Amortized Cost		19,453	1,652
Gross Unrealized Gains		3
Gross Unrealized Losses		5
Short-term investments		$ 19,451	$ 1,652	[2]

[1] As of September 24, 2016 there were $10.5 million of investments in our portfolio in a loss position. As of December 26, 2015 there were no investments in our portfolio in a loss position

[2] Derived from December 26, 2015 audited financial statements