Quarterly report pursuant to Section 13 or 15(d)

Marketable Securities and Fair Value Measurements - Financial Assets at Fair Value on Recurring Basis (Detail)

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Marketable Securities and Fair Value Measurements - Financial Assets at Fair Value on Recurring Basis (Detail) - USD ($)
$ in Thousands
Sep. 30, 2019
Dec. 31, 2018
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total cash equivalents and marketable securities $ 51,305 $ 95,668
Cash and cash equivalents 15,268 87,721
Marketable securities, current 36,147 10,234
Cash Equivalents    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Cash and cash equivalents 15,158 85,434
Money Market Funds    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total cash equivalents and marketable securities 14,261 82,843
Commercial Paper    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total cash equivalents and marketable securities 19,841 12,825
United States Treasury Bills    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total cash equivalents and marketable securities 7,246  
United States Government-Related Debt Securities    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total cash equivalents and marketable securities 7,006  
Corporate Bonds    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total cash equivalents and marketable securities 2,951  
Basis of Fair Value Measurements, Level 1    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total cash equivalents and marketable securities 14,261 82,843
Basis of Fair Value Measurements, Level 1 | Money Market Funds    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total cash equivalents and marketable securities 14,261 82,843
Basis of Fair Value Measurements, Level 1 | Commercial Paper    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total cash equivalents and marketable securities 0 0
Basis of Fair Value Measurements, Level 1 | United States Treasury Bills    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total cash equivalents and marketable securities 0  
Basis of Fair Value Measurements, Level 1 | Corporate Bonds    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total cash equivalents and marketable securities 0  
Basis of Fair Value Measurements, Level 2    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total cash equivalents and marketable securities 37,044 12,825
Basis of Fair Value Measurements, Level 2 | Money Market Funds    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total cash equivalents and marketable securities 0 0
Basis of Fair Value Measurements, Level 2 | Commercial Paper    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total cash equivalents and marketable securities 19,841 12,825
Basis of Fair Value Measurements, Level 2 | United States Treasury Bills    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total cash equivalents and marketable securities 7,246  
Basis of Fair Value Measurements, Level 2 | United States Government-Related Debt Securities    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total cash equivalents and marketable securities 7,006  
Basis of Fair Value Measurements, Level 2 | Corporate Bonds    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total cash equivalents and marketable securities 2,951  
Basis of Fair Value Measurements, Level 3    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total cash equivalents and marketable securities 0 0
Basis of Fair Value Measurements, Level 3 | Money Market Funds    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total cash equivalents and marketable securities 0 0
Basis of Fair Value Measurements, Level 3 | Commercial Paper    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total cash equivalents and marketable securities 0 $ 0
Basis of Fair Value Measurements, Level 3 | United States Treasury Bills    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total cash equivalents and marketable securities $ 0