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Fair Value Measurements - Money Market Funds (Details) - Level 1 - USD ($) $ in Thousands | Sep. 30, 2021 | Dec. 31, 2020 | Dec. 31, 2019
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Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |  |
Cash equivalents | $ 24,461 | $ 24,460 | $ 24,379
Money Market Funds [Member] |  |  |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |  |  |
Cash equivalents | $ 24,461 | $ 24,460 | $ 24,379

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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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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
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- Details
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- Details
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