Annual report pursuant to Section 13 and 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
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]      
Total cash equivalents and marketable securities $ 95,668 $ 51,751  
Cash and cash equivalents 87,721 58,910 $ 1,716
Marketable securities, current 10,234 0  
Cash Equivalents      
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]      
Cash and cash equivalents 85,434 51,751  
Money Market Funds      
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]      
Total cash equivalents and marketable securities 82,843 51,751  
Commercial Paper      
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]      
Total cash equivalents and marketable securities 12,825 0  
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 82,843 51,751  
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 82,843 51,751  
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 2      
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]      
Total cash equivalents and marketable securities 12,825 0  
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 12,825 0  
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