| Fair value measurements (Details) - USD ($) $ in Thousands | Jun. 30, 2021 | Dec. 31, 2020 | 
|---|---|---|
| Marketable securities: | ||
| Available-for-sale securities, Debt Securities, Current, Total | $ 234,917 | $ 311,335 | 
| Recurring basis | ||
| Marketable securities: | ||
| Available-for-sale securities, Debt Securities, Current, Total | 234,917 | |
| Recurring basis | Corporate debt securities | ||
| Marketable securities: | ||
| Available-for-sale securities, Debt Securities, Current, Total | 234,917 | |
| Recurring basis | Level 1 | ||
| Marketable securities: | ||
| Available-for-sale securities, Debt Securities, Current, Total | 234,917 | |
| Recurring basis | Level 1 | Corporate debt securities | ||
| Marketable securities: | ||
| Available-for-sale securities, Debt Securities, Current, Total | $ 234,917 | 
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- Definition Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), classified as current. Reference 1: http://www.xbrl.org/2003/role/disclosureRef 
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- References No definition available. 
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