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Summary of Significant Accounting Policies - Summary of Assets Measured at Fair Value on Recurring Basis (Details) - Fair Value, Measurements, Recurring - USD ($)
$ in Thousands
Sep. 30, 2019
Dec. 31, 2018
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Assets measured at fair value on a recurring basis $ 117,262 $ 108,028
Cash    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Assets measured at fair value on a recurring basis 8  
Money Market Funds | Cash and Cash Equivalents    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Assets measured at fair value on a recurring basis 23,613 6,804
U.S. Treasury Securities | Cash and Cash Equivalents    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Assets measured at fair value on a recurring basis   238
U.S. Treasury Securities | Marketable Securities    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Assets measured at fair value on a recurring basis 93,641 100,986
Active Markets (Level 1)    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Assets measured at fair value on a recurring basis 117,262 108,028
Active Markets (Level 1) | Cash    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Assets measured at fair value on a recurring basis 8  
Active Markets (Level 1) | Money Market Funds | Cash and Cash Equivalents    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Assets measured at fair value on a recurring basis 23,613 6,804
Active Markets (Level 1) | U.S. Treasury Securities | Cash and Cash Equivalents    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Assets measured at fair value on a recurring basis   238
Active Markets (Level 1) | U.S. Treasury Securities | Marketable Securities    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Assets measured at fair value on a recurring basis $ 93,641 $ 100,986