Note 3 - Financial Instruments Measured at Fair Value - Effective Maturities of Short-term Investments (Details) - USD ($) $ in Thousands	Jun. 24, 2017	Dec. 31, 2016
Due in one year or less, amortized cost	$ 21,198	$ 31,372
Due in one year or less, estimated fair value	21,194	31,367
Due after one year through three years, amortized cost	616	623
Due after one year through three years, estimated fair value	616	623
Total amortized cost	21,814	31,995
Total estimated fair value	$ 21,810	$ 31,990