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Note 3 - Financial Instruments - Instruments by Significant Investment Category (Details) - Fair Value, Inputs, Level 1 [Member] - USD ($)
$ in Thousands
9 Months Ended 12 Months Ended
Sep. 30, 2023
Dec. 31, 2022
Adjusted Cost $ 10,000 $ 13,849
Unrealized Gains 0 100
Unrealized Losses 0 0
Market Value 10,000 13,949
US Treasury Securities in Short-term Investments [Member]    
Adjusted Cost   9,849
Unrealized Gains   100
Unrealized Losses   0
Market Value   9,949
Certificates of Deposit [Member]    
Adjusted Cost 10,000 4,000
Unrealized Gains 0 0
Unrealized Losses 0 0
Market Value $ 10,000 $ 4,000