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Fair Value Measurements and Available for Sale Investments - Assets and Liabilities Measured at Fair Value on a Recurring Basis (Details) - USD ($) $ in Thousands | Jun. 30, 2021 | Dec. 31, 2020
--- | --- | ---
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Available-for-sale securities, debt securities | $ 64,081 | $ 160,743
US Treasury Securities |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Available-for-sale securities, debt securities | 45,714 | 107,697
Certificates of deposit |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Available-for-sale securities, debt securities | 1,591 | 2,436
Agency securities |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Available-for-sale securities, debt securities | 4,997 | 21,169
Commercial and corporate obligations |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Available-for-sale securities, debt securities | 11,779 | 29,441
Recurring | US Treasury Securities |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Available-for-sale securities, debt securities | 45,714 | 107,697
Recurring | Certificates of deposit |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Available-for-sale securities, debt securities | 1,591 | 2,436
Recurring | Agency securities |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Available-for-sale securities, debt securities | 4,997 | 21,169
Recurring | Commercial and corporate obligations |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Available-for-sale securities, debt securities | 11,779 | 29,441
Recurring | Money market funds |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments at fair value | 305,162 | 188,297
Recurring | Mutual funds |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments at fair value | 26,928 | 57,153
Recurring | Quoted Market Prices for Identical Assets (Level 1) | US Treasury Securities |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Available-for-sale securities, debt securities | 45,714 | 107,697
Recurring | Quoted Market Prices for Identical Assets (Level 1) | Certificates of deposit |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Available-for-sale securities, debt securities | 0 | 0
Recurring | Quoted Market Prices for Identical Assets (Level 1) | Agency securities |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Available-for-sale securities, debt securities | 0 | 0
Recurring | Quoted Market Prices for Identical Assets (Level 1) | Commercial and corporate obligations |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Available-for-sale securities, debt securities | 0 | 0
Recurring | Quoted Market Prices for Identical Assets (Level 1) | Money market funds |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments at fair value | 305,162 | 188,297
Recurring | Quoted Market Prices for Identical Assets (Level 1) | Mutual funds |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments at fair value | 26,928 | 57,153
Recurring | Significant Other Observable Inputs (Level 2) | US Treasury Securities |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Available-for-sale securities, debt securities | 0 | 0
Recurring | Significant Other Observable Inputs (Level 2) | Certificates of deposit |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Available-for-sale securities, debt securities | 1,591 | 2,436
Recurring | Significant Other Observable Inputs (Level 2) | Agency securities |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Available-for-sale securities, debt securities | 4,997 | 21,169
Recurring | Significant Other Observable Inputs (Level 2) | Commercial and corporate obligations |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Available-for-sale securities, debt securities | 11,779 | 29,441
Recurring | Significant Other Observable Inputs (Level 2) | Money market funds |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments at fair value | 0 | 0
Recurring | Significant Other Observable Inputs (Level 2) | Mutual funds |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments at fair value | 0 | 0
Recurring | Significant Unobservable Inputs (Level 3) | US Treasury Securities |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Available-for-sale securities, debt securities | 0 | 0
Recurring | Significant Unobservable Inputs (Level 3) | Certificates of deposit |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Available-for-sale securities, debt securities | 0 | 0
Recurring | Significant Unobservable Inputs (Level 3) | Agency securities |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Available-for-sale securities, debt securities | 0 | 0
Recurring | Significant Unobservable Inputs (Level 3) | Commercial and corporate obligations |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Available-for-sale securities, debt securities | 0 | 0
Recurring | Significant Unobservable Inputs (Level 3) | Money market funds |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments at fair value | 0 | 0
Recurring | Significant Unobservable Inputs (Level 3) | Mutual funds |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Investments at fair value | $ 0 | $ 0

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