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Cash Equivalents and Marketable Securities - Classification of Cash Equivalents and Marketable Securities (Details) - USD ($) $ in Thousands | 9 Months Ended | 12 Months Ended
--- | --- | ---
Sep. 30, 2021 | Dec. 31, 2020
Classified as: |  |
Cash equivalents | $ 116,068 | $ 113,693
Marketable securities - current | 193,759 | 188,451
Marketable securities - noncurrent | 38,169 | 2,000
Total cash equivalents and marketable securities | $ 347,996 | $ 304,144
Contractual maturities |  |
Maximum period of current contractual maturities | 1 year | 1 year
Minimum period of noncurrent contractual maturities | 1 year | 1 year
Maximum period of Noncurrent contractual maturities | 2 years | 2 years

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- Definition Amount of 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. Excludes cash and cash equivalents within disposal group and discontinued operation. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.1) -URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682 + Details
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