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Financial Instruments - Fair value hierarchy (Details) - USD ($) $ in Thousands | 3 Months Ended | 9 Months Ended |
--- | --- | --- | ---
Sep. 30, 2022 | Sep. 30, 2021 | Sep. 30, 2022 | Sep. 30, 2021 | Dec. 31, 2021
Financial Instruments |  |  |  |  |
Transfers between fair value measurement levels | $ 0 | $ 0 | $ 0 | $ 0 |
Reverse repurchase agreements | Government Securities and Obligations |  |  |  |  |
Financial Instruments |  |  |  |  |
Percentage of investment amount to collateralized deposits value |  |  | 102.00% |  |
Recurring |  |  |  |  |
Assets: |  |  |  |  |
Total | 87,779 |  | $ 87,779 |  | $ 40,853
Recurring | Level 1 |  |  |  |  |
Assets: |  |  |  |  |
Total | 14,510 |  | 14,510 |  | 1,853
Recurring | Level 2 |  |  |  |  |
Assets: |  |  |  |  |
Total | 73,269 |  | 73,269 |  | 39,000
Recurring | Money market funds |  |  |  |  |
Assets: |  |  |  |  |
Cash and cash equivalents: | 8,581 |  | 8,581 |  | 1,853
Recurring | Money market funds | Level 1 |  |  |  |  |
Assets: |  |  |  |  |
Cash and cash equivalents: | 8,581 |  | 8,581 |  | 1,853
Recurring | Corporate debt securities |  |  |  |  |
Assets: |  |  |  |  |
Cash and cash equivalents: | 599 |  | 599 |  |
Short term investments | 26,228 |  | 26,228 |  |
Recurring | Corporate debt securities | Level 2 |  |  |  |  |
Assets: |  |  |  |  |
Cash and cash equivalents: | 599 |  | 599 |  |
Short term investments | 26,228 |  | 26,228 |  |
Recurring | Yankee securities |  |  |  |  |
Assets: |  |  |  |  |
Short term investments | 4,969 |  | 4,969 |  |
Recurring | Yankee securities | Level 2 |  |  |  |  |
Assets: |  |  |  |  |
Short term investments | 4,969 |  | 4,969 |  |
Recurring | Bonds |  |  |  |  |
Assets: |  |  |  |  |
Short term investments | 2,973 |  | 2,973 |  |
Recurring | Bonds | Level 2 |  |  |  |  |
Assets: |  |  |  |  |
Short term investments | 2,973 |  | 2,973 |  |
Recurring | Treasury bill |  |  |  |  |
Assets: |  |  |  |  |
Short term investments | 5,929 |  | 5,929 |  |
Recurring | Treasury bill | Level 1 |  |  |  |  |
Assets: |  |  |  |  |
Short term investments | 5,929 |  | 5,929 |  |
Recurring | Reverse repurchase agreements |  |  |  |  |
Assets: |  |  |  |  |
Cash and cash equivalents: | 8,000 |  | 8,000 |  |
Short term investments | 30,500 |  | 30,500 |  | 39,000
Recurring | Reverse repurchase agreements | Level 2 |  |  |  |  |
Assets: |  |  |  |  |
Cash and cash equivalents: | 8,000 |  | 8,000 |  |
Short term investments | $ 30,500 |  | $ 30,500 |  | $ 39,000

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