Note 5 - Financial Instruments Measured at Fair Value - Effective Maturities of Short-term Investments (Details) - USD ($) $ in Thousands	Jun. 25, 2022	Dec. 25, 2021
Due in one year or less	$ 71,917	$ 83,429
Due in one year or less, fair value	71,636	83,408
Due after one year through three years	16,111	6,309
Due after one year through three years, fair value	15,859	6,296
Debt Securities, Available-for-Sale, Maturity, Allocated and Single Maturity Date, Amortized Cost, Total	88,028	89,738
Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, Fair Value, Total	$ 87,495	$ 89,704