Summary of Significant Accounting Policies - Fair value of financial instruments (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Recurring \| Level 1 \| Money market funds
Fair value of financial instruments
Cash equivalents	$ 50,395	$ 72,889

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