Quarterly report pursuant to Section 13 or 15(d)

Short-term Investments - Summary of Hierarchy for Assets Measured at Fair Value on a Recurring Basis (Detail)

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Short-term Investments - Summary of Hierarchy for Assets Measured at Fair Value on a Recurring Basis (Detail) - Fair Value, Measurements, Recurring [Member] - USD ($)
$ in Thousands
Jun. 30, 2019
Dec. 31, 2018
U.S. Government Securities [Member]    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total Fair Value $ 19,923  
U.S. T-bills [Member]    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total Fair Value 9,971  
U.S. Agency Securities [Member]    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total Fair Value 6,707  
Money market funds [Member]    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total Fair Value 8,168 $ 61,134
Quoted Market Prices for Identical Assets (Level 1) [Member] | U.S. Government Securities [Member]    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total Fair Value 19,923  
Quoted Market Prices for Identical Assets (Level 1) [Member] | U.S. T-bills [Member]    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total Fair Value 9,971  
Quoted Market Prices for Identical Assets (Level 1) [Member] | Money market funds [Member]    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total Fair Value 8,168 $ 61,134
Significant Other Observable Inputs (Level 2) [Member] | U.S. Agency Securities [Member]    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total Fair Value $ 6,707