Note 4 - Investments and Fair Value Measurements - Investments Measured at Fair Value (Details) - USD ($) $ in Thousands | Sep. 30, 2023 | Dec. 31, 2022 |
Debt securities, held-to-maturity, net of allowance for credit losses, fair value | | $ 23,320 | $ 88,524 |
Available-for-sale debt securities, at fair value (amortized cost $58,311 at September 30, 2023 and $59,191 at December 31, 2022) | | 57,327 | 58,254 |
Corporate Debt Securities [Member] | | | |
Available-for-sale debt securities, at fair value (amortized cost $58,311 at September 30, 2023 and $59,191 at December 31, 2022) | [1] | 25,592 | 26,888 |
US Treasury Securities [Member] | | | |
Available-for-sale debt securities, at fair value (amortized cost $58,311 at September 30, 2023 and $59,191 at December 31, 2022) | | 30,272 | 29,923 |
Debt Security, Government, Non-US [Member] | | | |
Available-for-sale debt securities, at fair value (amortized cost $58,311 at September 30, 2023 and $59,191 at December 31, 2022) | | 1,463 | 1,443 |
Fair Value, Recurring [Member] | | | |
Debt securities, held-to-maturity, net of allowance for credit losses, fair value | | 23,527 | 88,964 |
Available-for-sale debt securities, at fair value (amortized cost $58,311 at September 30, 2023 and $59,191 at December 31, 2022) | | 57,327 | 58,254 |
Mortgage loans | | 46 | 297 |
Total | | 80,900 | 147,515 |
Liabilities, fair value | | 179 | 566 |
Fair Value, Recurring [Member] | Corporate Debt Securities [Member] | | | |
Debt securities, held-to-maturity, net of allowance for credit losses, fair value | | 19,081 | 59,673 |
Available-for-sale debt securities, at fair value (amortized cost $58,311 at September 30, 2023 and $59,191 at December 31, 2022) | | 25,592 | 26,888 |
Fair Value, Recurring [Member] | US Treasury Securities [Member] | | | |
Debt securities, held-to-maturity, net of allowance for credit losses, fair value | | 4,009 | 23,987 |
Available-for-sale debt securities, at fair value (amortized cost $58,311 at September 30, 2023 and $59,191 at December 31, 2022) | | 30,272 | 29,923 |
Fair Value, Recurring [Member] | Debt Security, Government, Non-US [Member] | | | |
Debt securities, held-to-maturity, net of allowance for credit losses, fair value | | 0 | 4,999 |
Available-for-sale debt securities, at fair value (amortized cost $58,311 at September 30, 2023 and $59,191 at December 31, 2022) | | 1,463 | 1,443 |
Fair Value, Recurring [Member] | Certificates of Deposit [Member] | | | |
Debt securities, held-to-maturity, net of allowance for credit losses, fair value | | 437 | 305 |
Fair Value, Recurring [Member] | Public Warrants [Member] | | | |
Liabilities, fair value | | 54 | 230 |
Fair Value, Recurring [Member] | Private Placement Warrants [Member] | | | |
Liabilities, fair value | | 27 | 117 |
Fair Value, Recurring [Member] | Sponsor Covered Shares [Member] | | | |
Liabilities, fair value | | 98 | 219 |
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | | | |
Debt securities, held-to-maturity, net of allowance for credit losses, fair value | | 4,009 | 23,987 |
Available-for-sale debt securities, at fair value (amortized cost $58,311 at September 30, 2023 and $59,191 at December 31, 2022) | | 30,272 | 29,923 |
Mortgage loans | | 0 | 0 |
Total | | 34,281 | 53,910 |
Liabilities, fair value | | 54 | 230 |
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Corporate Debt Securities [Member] | | | |
Debt securities, held-to-maturity, net of allowance for credit losses, fair value | | 0 | 0 |
Available-for-sale debt securities, at fair value (amortized cost $58,311 at September 30, 2023 and $59,191 at December 31, 2022) | | 0 | 0 |
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | US Treasury Securities [Member] | | | |
Debt securities, held-to-maturity, net of allowance for credit losses, fair value | | 4,009 | 23,987 |
Available-for-sale debt securities, at fair value (amortized cost $58,311 at September 30, 2023 and $59,191 at December 31, 2022) | | 30,272 | 29,923 |
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Debt Security, Government, Non-US [Member] | | | |
Debt securities, held-to-maturity, net of allowance for credit losses, fair value | | 0 | 0 |
Available-for-sale debt securities, at fair value (amortized cost $58,311 at September 30, 2023 and $59,191 at December 31, 2022) | | 0 | 0 |
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Certificates of Deposit [Member] | | | |
Debt securities, held-to-maturity, net of allowance for credit losses, fair value | | 0 | 0 |
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Public Warrants [Member] | | | |
Liabilities, fair value | | 54 | 230 |
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Private Placement Warrants [Member] | | | |
Liabilities, fair value | | 0 | 0 |
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Sponsor Covered Shares [Member] | | | |
Liabilities, fair value | | 0 | 0 |
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | | | |
Debt securities, held-to-maturity, net of allowance for credit losses, fair value | | 19,518 | 64,977 |
Available-for-sale debt securities, at fair value (amortized cost $58,311 at September 30, 2023 and $59,191 at December 31, 2022) | | 27,055 | 28,331 |
Mortgage loans | | 0 | 0 |
Total | | 46,573 | 93,308 |
Liabilities, fair value | | 27 | 117 |
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Corporate Debt Securities [Member] | | | |
Debt securities, held-to-maturity, net of allowance for credit losses, fair value | | 19,081 | 59,673 |
Available-for-sale debt securities, at fair value (amortized cost $58,311 at September 30, 2023 and $59,191 at December 31, 2022) | | 25,592 | 26,888 |
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | US Treasury Securities [Member] | | | |
Debt securities, held-to-maturity, net of allowance for credit losses, fair value | | 0 | 0 |
Available-for-sale debt securities, at fair value (amortized cost $58,311 at September 30, 2023 and $59,191 at December 31, 2022) | | 0 | 0 |
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Debt Security, Government, Non-US [Member] | | | |
Debt securities, held-to-maturity, net of allowance for credit losses, fair value | | 0 | 4,999 |
Available-for-sale debt securities, at fair value (amortized cost $58,311 at September 30, 2023 and $59,191 at December 31, 2022) | | 1,463 | 1,443 |
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Certificates of Deposit [Member] | | | |
Debt securities, held-to-maturity, net of allowance for credit losses, fair value | | 437 | 305 |
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Public Warrants [Member] | | | |
Liabilities, fair value | | 0 | 0 |
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Private Placement Warrants [Member] | | | |
Liabilities, fair value | | 27 | 117 |
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Sponsor Covered Shares [Member] | | | |
Liabilities, fair value | | 0 | 0 |
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | | | |
Debt securities, held-to-maturity, net of allowance for credit losses, fair value | | 0 | 0 |
Available-for-sale debt securities, at fair value (amortized cost $58,311 at September 30, 2023 and $59,191 at December 31, 2022) | | 0 | 0 |
Mortgage loans | | 46 | 297 |
Total | | 46 | 297 |
Liabilities, fair value | | 98 | 219 |
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Corporate Debt Securities [Member] | | | |
Debt securities, held-to-maturity, net of allowance for credit losses, fair value | | 0 | 0 |
Available-for-sale debt securities, at fair value (amortized cost $58,311 at September 30, 2023 and $59,191 at December 31, 2022) | | 0 | 0 |
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | US Treasury Securities [Member] | | | |
Debt securities, held-to-maturity, net of allowance for credit losses, fair value | | 0 | 0 |
Available-for-sale debt securities, at fair value (amortized cost $58,311 at September 30, 2023 and $59,191 at December 31, 2022) | | 0 | 0 |
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Debt Security, Government, Non-US [Member] | | | |
Debt securities, held-to-maturity, net of allowance for credit losses, fair value | | 0 | 0 |
Available-for-sale debt securities, at fair value (amortized cost $58,311 at September 30, 2023 and $59,191 at December 31, 2022) | | 0 | 0 |
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Certificates of Deposit [Member] | | | |
Debt securities, held-to-maturity, net of allowance for credit losses, fair value | | 0 | 0 |
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Public Warrants [Member] | | | |
Liabilities, fair value | | 0 | 0 |
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Private Placement Warrants [Member] | | | |
Liabilities, fair value | | 0 | 0 |
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Sponsor Covered Shares [Member] | | | |
Liabilities, fair value | | $ 98 | $ 219 |
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[1]Includes both U.S. and foreign corporate debt securities. | |