Fair value of financial instruments - Fair value (Details) - Recurring basis - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Financial assets
Cash equivalents	$ 22,634	$ 65,610
Short-term investments	79,102	73,444
Long-term investments		5,995
Total financial assets	101,736	145,049
Level 1
Financial assets
Cash equivalents	22,634	60,611
Total financial assets	22,634	60,611
Level 2
Financial assets
Cash equivalents		4,999
Short-term investments	79,102	73,444
Long-term investments		5,995
Total financial assets	$ 79,102	$ 84,438

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.

No definition available.

Name:	us-gaap_CashAndCashEquivalentsFairValueDisclosure
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant