Note 3 - Financial Instruments Measured at Fair Value - Effective Maturities of Short-term Investments (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Due in one year or less, amortized cost	$ 16,341	$ 31,372
Due in one year or less, estimated fair value	16,340	31,367
Due after one year through three years, amortized cost		623
Due after one year through three years, estimated fair value		623
Total amortized cost	16,341	31,995
Total estimated fair value	$ 16,340	$ 31,990