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Balance Sheet Account Details - Investment Categories (Details) - USD ($) $ in Thousands | Dec. 31, 2023 | Dec. 31, 2022
--- | --- | ---
Debt Securities, Available-for-sale |  |
Cost | $ 120,874 | $ 108,778
Gross unrealized gains | 79 | 415
Gross unrealized losses | (5,783) | (5,451)
Estimated fair value | 115,170 | 103,742
Bond Fund |  |
Debt Securities, Available-for-sale |  |
Cost | 63,763 | 81,815
Gross unrealized gains | 0 | 0
Gross unrealized losses | (537) | (1,050)
Estimated fair value | 63,226 | 80,765
Bank deposits |  |
Debt Securities, Available-for-sale |  |
Cost | 17,165 | 5,012
Gross unrealized gains | 12 | 2
Gross unrealized losses | (1) | (34)
Estimated fair value | 17,176 | 4,980
Corporate bonds |  |
Debt Securities, Available-for-sale |  |
Cost | 14,850 | 6,701
Gross unrealized gains | 40 | 13
Gross unrealized losses | (2) | (58)
Estimated fair value | 14,888 | 6,656
Commercial paper |  |
Debt Securities, Available-for-sale |  |
Cost | 11,578 | 7,211
Gross unrealized gains | 9 | 3
Gross unrealized losses | (1) | 0
Estimated fair value | 11,586 | 7,214
U.S. government securities |  |
Debt Securities, Available-for-sale |  |
Cost | 6,736 | 2,232
Gross unrealized gains | 18 | 0
Gross unrealized losses | (3) | (70)
Estimated fair value | 6,751 | 2,162
Municipal bonds |  |
Debt Securities, Available-for-sale |  |
Cost | 1,007 |
Gross unrealized gains | 0 |
Gross unrealized losses | (4) |
Estimated fair value | 1,003 |
Corporate equity securities |  |
Debt Securities, Available-for-sale |  |
Cost | 5,775 | 5,807
Gross unrealized gains | 0 | 262
Gross unrealized losses | (5,235) | (4,239)
Estimated fair value | $ 540 | 1,830
Warrants |  |
Debt Securities, Available-for-sale |  |
Cost |  | 0
Gross unrealized gains |  | 135
Gross unrealized losses |  | 0
Estimated fair value |  | $ 135

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