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Fair Value Measurements - Schedule of Financial Instruments (Excluding Restricted Cash) Measured at Fair Value on Recurring Basis (Details) - Fair Value On Recurring Basis - USD ($) $ in Thousands | Dec. 31, 2019 | Dec. 31, 2018
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Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Total assets measured at fair value | $ 188,270 | $ 259,725
Money Market Funds |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Total assets measured at fair value | 45,498 | 45,017
U.S. Government Agency Obligations |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Total assets measured at fair value | 74,854 | 103,940
Corporate Securities and Commercial Paper |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Total assets measured at fair value | 67,918 | 110,768
Level 1 |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Total assets measured at fair value | 45,498 | 45,017
Level 1 | Money Market Funds |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Total assets measured at fair value | 45,498 | 45,017
Level 2 |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Total assets measured at fair value | 142,772 | 214,708
Level 2 | U.S. Government Agency Obligations |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Total assets measured at fair value | 74,854 | 103,940
Level 2 | Corporate Securities and Commercial Paper |  |
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items] |  |
Total assets measured at fair value | $ 67,918 | $ 110,768

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