Note 5 - Financial Instruments Measured at Fair Value - Effective Maturities of Short-term Investments (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Due in one year or less, amortized cost	$ 70,275	$ 112,956
Due in one year or less, fair value	70,012	112,683
Due after one year through five years, amortized cost	23,536	30,996
Due after one year through five years, fair value	23,443	30,552
Due after five years through ten years, amortized cost	725	0
Due after five years through ten years, fair value	725	0
Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, Amortized Cost, Total	94,536	143,952
Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, Fair Value, Total	$ 94,180	$ 143,235