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Fair Value Measurements (Details) - USD ($) $ in Thousands | Sep. 30, 2021 | Dec. 31, 2020
--- | --- | ---
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Marketable securities | $ 231,224 |
Cash and cash equivalents |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Cash and cash equivalents - money market funds | 253,079 | $ 280,578
Marketable securities |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Marketable securities | 231,224 | 207,207
Commercial paper |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Marketable securities | 12,487 | 21,489
U.S. treasury debt securities |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Marketable securities | 52,731 | 51,809
Corporate debt securities |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Marketable securities | 160,968 | 147,882
Foreign government debt securities |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Marketable securities | 5,038 | 1,027
Money market funds |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Cash and cash equivalents - money market funds | 253,079 | 265,578
Level 2 |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Fair value of convertible debt | 641,800 |
Recurring |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Total assets measured at fair value | 484,303 | 487,785
Recurring | Cash and cash equivalents |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Cash and cash equivalents - money market funds | 253,079 | 280,578
Recurring | Marketable securities |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Marketable securities | 231,224 | 207,207
Recurring | Commercial paper |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Marketable securities | 12,487 | 21,489
Recurring | U.S. treasury debt securities |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Marketable securities | 52,731 | 51,809
Recurring | Corporate debt securities |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Marketable securities | 160,968 | 147,882
Recurring | Foreign government debt securities |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Marketable securities | 5,038 | 1,027
Recurring | Money market funds |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Cash and cash equivalents - money market funds | 253,079 | 265,578
Recurring | Level 1 |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Total assets measured at fair value | 253,079 | 265,578
Recurring | Level 1 | Commercial paper |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Marketable securities | 0 | 0
Recurring | Level 1 | U.S. treasury debt securities |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Marketable securities | 0 | 0
Recurring | Level 1 | Corporate debt securities |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Marketable securities | 0 | 0
Recurring | Level 1 | Foreign government debt securities |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Marketable securities | 0 | 0
Recurring | Level 1 | Money market funds |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Cash and cash equivalents - money market funds | 253,079 | 265,578
Recurring | Level 2 |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Total assets measured at fair value | 231,224 | 222,207
Recurring | Level 2 | Commercial paper |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Marketable securities | 12,487 | 21,489
Recurring | Level 2 | U.S. treasury debt securities |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Marketable securities | 52,731 | 51,809
Recurring | Level 2 | Corporate debt securities |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Marketable securities | 160,968 | 147,882
Recurring | Level 2 | Foreign government debt securities |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Marketable securities | 5,038 | 1,027
Recurring | Level 2 | Money market funds |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Cash and cash equivalents - money market funds | $ 0 | $ 0

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