Annual report pursuant to Section 13 and 15(d)

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

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Fair Value Measurements and Marketable Securities - Financial Assets at Fair Value on Recurring Basis (Detail) - USD ($)
$ in Thousands
Dec. 31, 2016
Dec. 31, 2015
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total cash equivalents and marketable securities $ 23,217 $ 48,510
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 2,746 5,421
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 20,471 43,089
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
Money Market Funds    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total cash equivalents and marketable securities 2,746 5,421
Money Market Funds | 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 2,746 5,421
Money Market Funds | 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 0 0
Money Market Funds | 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
Corporate Debt Securities    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total cash equivalents and marketable securities 4,206 12,571
Corporate Debt Securities | 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 0 0
Corporate Debt Securities | 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 4,206 12,571
Corporate Debt Securities | 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
Government Securities    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total cash equivalents and marketable securities 5,299 21,769
Government Securities | 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 0 0
Government Securities | 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 5,299 21,769
Government Securities | 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
Commercial Paper    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total cash equivalents and marketable securities 10,966 6,145
Commercial Paper | 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 0 0
Commercial Paper | 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 10,966 6,145
Commercial Paper | 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
Certificates of Deposit    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total cash equivalents and marketable securities   696
Certificates of Deposit | 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   0
Certificates of Deposit | 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   696
Certificates of Deposit | 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
Municipal Securities    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total cash equivalents and marketable securities   1,908
Municipal Securities | 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   0
Municipal Securities | 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   1,908
Municipal Securities | 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