Note 4 - Financial Instruments Measured at Fair Value - Short-Term Investments by Security Type (Details) - USD ($) $ in Thousands	Sep. 26, 2015	Dec. 27, 2014
Foreign Government Debt Securities [Member]
Investments, Amortized Cost	$ 465
Investments, Estimated Fair Value	465
Municipal Bonds [Member]
Investments, Amortized Cost		$ 155
Investments, Estimated Fair Value		155
Certificates of Deposit [Member]
Investments, Amortized Cost	1,002	1,000
Investments, Estimated Fair Value	1,002	1,000
Investments, Amortized Cost	1,467	1,155
Investments, Estimated Fair Value	$ 1,467	$ 1,155	[1]

[1] Derived from December 27, 2014 audited financial statements