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
Jun. 30, 2019
Dec. 31, 2018
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total cash equivalents and marketable securities $ 71,470 $ 95,668
Cash and cash equivalents 16,795 87,721
Marketable securities, current 55,529 10,234
Cash Equivalents    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Cash and cash equivalents 15,941 85,434
Money Market Funds    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total cash equivalents and marketable securities 14,443 82,843
Commercial Paper    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total cash equivalents and marketable securities 32,787 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 13,991  
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 5,502  
Corporate Bonds    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total cash equivalents and marketable securities 4,747  
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 14,443 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 14,443 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 57,027 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 32,787 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 13,991  
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 5,502  
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 4,747  
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