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
Jun. 30, 2014
Dec. 31, 2013
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total cash equivalents and marketable securities $ 75,215 $ 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 6,463 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 68,752 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      
Money Market Funds
   
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total cash equivalents and marketable securities 6,463 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 6,463 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      
Certificates of Deposit
   
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total cash equivalents and marketable securities 2,844 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 2,844 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      
Corporate Debt Securities
   
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total cash equivalents and marketable securities 40,937 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 40,937 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      
U. S. Government Securities
   
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total cash equivalents and marketable securities 20,023 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 20,023 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      
Municipal Securities
   
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total cash equivalents and marketable securities 1,450 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 1,450 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      
Commercial Paper
   
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Total cash equivalents and marketable securities 3,498 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 3,498 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