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Fair Value Measurements and Short-Term Investments - Schedule of Short-Term Investments Subject to Fair Value Measurements on a Recurring Basis (Details) - USD ($)
$ in Thousands
Dec. 31, 2020
Dec. 31, 2019
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Amortized Cost $ 256,292 $ 279,284
Gross Unrealized Holding Gains 6 110
Aggregate Fair Value 256,298 279,394
Cash and cash equivalents 191,859 188,425
Level I | Money market funds    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Cash and cash equivalents 131,121 170,757
Level I | Restricted cash (money market funds)    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Restricted cash 917 917
Level I | U. S. Government bonds    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Short-term Investments, Amortized Cost 124,254 107,610
Short-term Investments, Gross Unrealized Holding Gains 6 110
Short-term Investments, Aggregate Fair Value $ 124,260 $ 107,720