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Financial Instruments - Fair value hierarchy (Details) - USD ($) $ in Thousands | 6 Months Ended |  |
--- | --- | --- | ---
Jun. 30, 2021 | Dec. 31, 2020 | Jun. 30, 2020
Financial Instruments |  |  |
Fair value assets, transfers from Level 1 to Level 2 | $ 0 |  | $ 0
Fair value assets, transfers from Level 2 to Level 1 | 0 |  | 0
Fair value liabilities, transfers from Level 1 to Level 2 | 0 |  | 0
Fair value liabilities, transfers from Level 2 to Level 1 | $ 0 |  | $ 0
Reverse repurchase agreements | Government Securities and Obligations | Minimum |  |  |
Financial Instruments |  |  |
Percentage of investment amount to collateralized deposits value | 102.00% |  |
Recurring |  |  |
Assets: |  |  |
Total assets | $ 40,841 | $ 42,999 |
Recurring | Level 1 |  |  |
Assets: |  |  |
Total assets | 1,841 | 22,999 |
Recurring | Level 2 |  |  |
Assets: |  |  |
Total assets | 39,000 | 20,000 |
Recurring | Money market fund |  |  |
Assets: |  |  |
Cash and cash equivalents | 1,841 | 22,999 |
Recurring | Money market fund | Level 1 |  |  |
Assets: |  |  |
Cash and cash equivalents | 1,841 | 22,999 |
Recurring | Reverse repurchase agreements |  |  |
Assets: |  |  |
Cash and cash equivalents | 39,000 |  |
Short-term investments |  | 20,000 |
Recurring | Reverse repurchase agreements | Level 2 |  |  |
Assets: |  |  |
Cash and cash equivalents | $ 39,000 |  |
Short-term investments |  | $ 20,000 |

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- Definition Fair value portion of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates. + References No definition available. + Details
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