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Short-term investments (Tables) | 9 Months Ended
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Sep. 30, 2021
Short-term investments |
Schedule of short-term investments by investment type | Short-term investments by investment type consisted of the following (in thousands): ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ |  | December 31, 2020
​ | ​ | ​ | ​ | ​ | Gross | ​ | Gross | ​ | ​ | ​
​ |  | Amortized |  | unrealized |  | unrealized |  | Fair
​ |  | cost |  | gains |  | losses |  | value
U.S. Treasury bonds | ​ | $ | 14,997 | ​ | $ | 1 | ​ | $ | — | ​ | $ | 14,998
​ | ​ | $ | 14,997 | ​ | $ | 1 | ​ | $ | — | ​ | $ | 14,998

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- Definition Tabular disclosure of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale). + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -URI http://asc.fasb.org/topic&trid=2196928 + Details
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