Fair Value Measurements and Available for Sale Investments - Schedule of Available for sale Investments by Security Type (Details) $ in Thousands	Sep. 30, 2019 USD ($)
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale Investments, Amortized Cost	$ 315,309
Available-for-sale Investments, Gross Unrealized Gains	464
Available-for-sale Investments, Gross Unrealized Losses	(9)
Available-for-sale Investments, Total Fair Value	315,764
U S Treasury and Agency Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale Investments, Amortized Cost	185,844
Available-for-sale Investments, Gross Unrealized Gains	145
Available-for-sale Investments, Gross Unrealized Losses	(4)
Available-for-sale Investments, Total Fair Value	185,985
Commercial Paper
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale Investments, Amortized Cost	29,887
Available-for-sale Investments, Total Fair Value	29,887
Corporate Debt Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale Investments, Amortized Cost	99,578
Available-for-sale Investments, Gross Unrealized Gains	319
Available-for-sale Investments, Gross Unrealized Losses	(5)
Available-for-sale Investments, Total Fair Value	$ 99,892

Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amount, before tax, of unrealized loss in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

+ References

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