Note 4 - Investments and Fair Value Measurements - Investments Measured at Fair Value (Details) - USD ($) $ in Thousands | Mar. 31, 2024 | Dec. 31, 2023 |
Debt securities, held-to-maturity, net of allowance for credit losses, fair value | | $ 16,232 | $ 17,745 |
Available-for-sale debt securities, at fair value (amortized cost $50,800 at March 31, 2024 and $58,516 at December 31, 2023) | | 50,395 | 58,032 |
Corporate Debt Securities [Member] | | | |
Available-for-sale debt securities, at fair value (amortized cost $50,800 at March 31, 2024 and $58,516 at December 31, 2023) | [1] | 24,480 | 25,933 |
US Treasury Securities [Member] | | | |
Available-for-sale debt securities, at fair value (amortized cost $50,800 at March 31, 2024 and $58,516 at December 31, 2023) | | 24,421 | 30,615 |
Debt Security, Government, Non-US [Member] | | | |
Available-for-sale debt securities, at fair value (amortized cost $50,800 at March 31, 2024 and $58,516 at December 31, 2023) | | 1,494 | 1,484 |
Fair Value, Recurring [Member] | | | |
Debt securities, held-to-maturity, net of allowance for credit losses, fair value | | 16,355 | 17,870 |
Available-for-sale debt securities, at fair value (amortized cost $50,800 at March 31, 2024 and $58,516 at December 31, 2023) | | 50,395 | 58,032 |
Mortgage loans | | 45 | 45 |
Total | | 66,795 | 75,947 |
Liabilities, fair value | | 350 | 112 |
Fair Value, Recurring [Member] | Corporate Debt Securities [Member] | | | |
Debt securities, held-to-maturity, net of allowance for credit losses, fair value | | 11,895 | 13,386 |
Available-for-sale debt securities, at fair value (amortized cost $50,800 at March 31, 2024 and $58,516 at December 31, 2023) | | 24,480 | 25,933 |
Fair Value, Recurring [Member] | US Treasury Securities [Member] | | | |
Debt securities, held-to-maturity, net of allowance for credit losses, fair value | | 4,022 | 4,047 |
Available-for-sale debt securities, at fair value (amortized cost $50,800 at March 31, 2024 and $58,516 at December 31, 2023) | | 24,421 | 30,615 |
Fair Value, Recurring [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 $50,800 at March 31, 2024 and $58,516 at December 31, 2023) | | 1,494 | 1,484 |
Fair Value, Recurring [Member] | Certificates of Deposit [Member] | | | |
Debt securities, held-to-maturity, net of allowance for credit losses, fair value | | 438 | 437 |
Fair Value, Recurring [Member] | Public Warrants [Member] | | | |
Liabilities, fair value | | 20 | 17 |
Fair Value, Recurring [Member] | Private Placement Warrants [Member] | | | |
Liabilities, fair value | | 9 | 9 |
Fair Value, Recurring [Member] | Sponsor Covered Shares [Member] | | | |
Liabilities, fair value | | 321 | 86 |
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | | | |
Debt securities, held-to-maturity, net of allowance for credit losses, fair value | | 4,022 | 4,047 |
Available-for-sale debt securities, at fair value (amortized cost $50,800 at March 31, 2024 and $58,516 at December 31, 2023) | | 24,421 | 30,615 |
Mortgage loans | | 0 | 0 |
Total | | 28,443 | 34,662 |
Liabilities, fair value | | 20 | 17 |
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 $50,800 at March 31, 2024 and $58,516 at December 31, 2023) | | 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 | | 4,022 | 4,047 |
Available-for-sale debt securities, at fair value (amortized cost $50,800 at March 31, 2024 and $58,516 at December 31, 2023) | | 24,421 | 30,615 |
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 $50,800 at March 31, 2024 and $58,516 at December 31, 2023) | | 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 | | 20 | 17 |
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 | | 12,333 | 13,823 |
Available-for-sale debt securities, at fair value (amortized cost $50,800 at March 31, 2024 and $58,516 at December 31, 2023) | | 25,974 | 27,417 |
Mortgage loans | | 0 | 0 |
Total | | 38,307 | 41,240 |
Liabilities, fair value | | 9 | 9 |
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 | | 11,895 | 13,386 |
Available-for-sale debt securities, at fair value (amortized cost $50,800 at March 31, 2024 and $58,516 at December 31, 2023) | | 24,480 | 25,933 |
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 $50,800 at March 31, 2024 and $58,516 at December 31, 2023) | | 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 | 0 |
Available-for-sale debt securities, at fair value (amortized cost $50,800 at March 31, 2024 and $58,516 at December 31, 2023) | | 1,494 | 1,484 |
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 | | 438 | 437 |
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 | | 9 | 9 |
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 $50,800 at March 31, 2024 and $58,516 at December 31, 2023) | | 0 | 0 |
Mortgage loans | | 45 | 45 |
Total | | 45 | 45 |
Liabilities, fair value | | 321 | 86 |
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 $50,800 at March 31, 2024 and $58,516 at December 31, 2023) | | 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 $50,800 at March 31, 2024 and $58,516 at December 31, 2023) | | 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 $50,800 at March 31, 2024 and $58,516 at December 31, 2023) | | 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 | | $ 321 | $ 86 |
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[1]Includes both U.S. and foreign corporate debt securities. | |