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Fair Value Measurement - Summary of Fair Value Measurements of Cash Equivalents, and Available-for-Sale Marketable Securities (Detail) - USD ($)
$ in Thousands
Sep. 30, 2016
Dec. 31, 2015
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total cash equivalents $ 27,115 $ 65,937
Total marketable securities 127,102 139,518
Total cash equivalents and marketable securities 154,217 205,455
Money market funds [Member]    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total cash equivalents 24,113 25,070
Commercial paper securities [Member]    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total cash equivalents   2,000
Total marketable securities 25,729 30,717
Level 1 [Member]    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total cash equivalents 24,113 65,937
Total cash equivalents and marketable securities 24,113 65,937
Level 1 [Member] | Money market funds [Member]    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total cash equivalents 24,113 25,070
Level 1 [Member] | Commercial paper securities [Member]    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total cash equivalents   2,000
Level 2 [Member]    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total cash equivalents 3,002  
Total marketable securities 127,102 139,518
Total cash equivalents and marketable securities 130,104 139,518
Level 2 [Member] | Commercial paper securities [Member]    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total marketable securities 25,729 30,717
U.S. government sponsored entity debt securities [Member]    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total cash equivalents 3,002 38,867
Total marketable securities 91,364 91,538
U.S. government sponsored entity debt securities [Member] | Level 1 [Member]    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total cash equivalents   38,867
U.S. government sponsored entity debt securities [Member] | Level 2 [Member]    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total cash equivalents 3,002  
Total marketable securities 91,364 91,538
Corporate debt securities [Member]    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total marketable securities 10,009 17,263
Corporate debt securities [Member] | Level 2 [Member]    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total marketable securities $ 10,009 $ 17,263