Quarterly report pursuant to Section 13 or 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, unless otherwise specified
Sep. 30, 2014
Dec. 31, 2013
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total cash equivalents and marketable securities $ 68,305 $ 82,033
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 6,175 4,285
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 62,130 77,748
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 6,175 4,285
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 6,175 4,285
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
Certificates of Deposit
    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total cash equivalents and marketable securities 2,554 1,584
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 2,554 1,584
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 0
Corporate Debt Securities
    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total cash equivalents and marketable securities 33,956 49,019
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 33,956 49,019
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
U. S. Government Securities
    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total cash equivalents and marketable securities 20,046 21,731
U. S. 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 20,046 21,731
U. S. 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
Municipal Securities
    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total cash equivalents and marketable securities 227 2,815
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 227 2,815
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 0
Commercial Paper
    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total cash equivalents and marketable securities 5,347 2,599
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 5,347 2,599
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