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
Mar. 31, 2014
Dec. 31, 2013
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total cash equivalents and marketable securities $ 86,386 $ 82,033
Money Market Funds [Member]
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total cash equivalents and marketable securities 5,001 4,285
Certificates of Deposit [Member]
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total cash equivalents and marketable securities 1,464 1,584
Corporate Debt Securities [Member]
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total cash equivalents and marketable securities 55,317 49,019
U. S. Government Securities [Member]
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total cash equivalents and marketable securities 18,990 21,731
Municipal Securities [Member]
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total cash equivalents and marketable securities 1,618 2,815
Commercial Paper [Member]
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total cash equivalents and marketable securities 3,996 2,599
Basis of Fair Value Measurements, Level 1 [Member]
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total cash equivalents and marketable securities 5,001 4,285
Basis of Fair Value Measurements, Level 1 [Member] | Money Market Funds [Member]
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total cash equivalents and marketable securities 5,001 4,285
Basis of Fair Value Measurements, Level 1 [Member] | Certificates of Deposit [Member]
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total cash equivalents and marketable securities      
Basis of Fair Value Measurements, Level 1 [Member] | Corporate Debt Securities [Member]
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total cash equivalents and marketable securities      
Basis of Fair Value Measurements, Level 1 [Member] | U. S. Government Securities [Member]
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total cash equivalents and marketable securities      
Basis of Fair Value Measurements, Level 1 [Member] | Municipal Securities [Member]
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total cash equivalents and marketable securities      
Basis of Fair Value Measurements, Level 1 [Member] | Commercial Paper [Member]
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total cash equivalents and marketable securities      
Basis of Fair Value Measurements, Level 2 [Member]
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total cash equivalents and marketable securities 81,385 77,748
Basis of Fair Value Measurements, Level 2 [Member] | Money Market Funds [Member]
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total cash equivalents and marketable securities      
Basis of Fair Value Measurements, Level 2 [Member] | Certificates of Deposit [Member]
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total cash equivalents and marketable securities 1,464 1,584
Basis of Fair Value Measurements, Level 2 [Member] | Corporate Debt Securities [Member]
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total cash equivalents and marketable securities 55,317 49,019
Basis of Fair Value Measurements, Level 2 [Member] | U. S. Government Securities [Member]
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total cash equivalents and marketable securities 18,990 21,731
Basis of Fair Value Measurements, Level 2 [Member] | Municipal Securities [Member]
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total cash equivalents and marketable securities 1,618 2,815
Basis of Fair Value Measurements, Level 2 [Member] | Commercial Paper [Member]
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total cash equivalents and marketable securities 3,996 2,599
Basis of Fair Value Measurements, Level 3 [Member]
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total cash equivalents and marketable securities      
Basis of Fair Value Measurements, Level 3 [Member] | Money Market Funds [Member]
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total cash equivalents and marketable securities      
Basis of Fair Value Measurements, Level 3 [Member] | Certificates of Deposit [Member]
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total cash equivalents and marketable securities      
Basis of Fair Value Measurements, Level 3 [Member] | Corporate Debt Securities [Member]
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total cash equivalents and marketable securities      
Basis of Fair Value Measurements, Level 3 [Member] | U. S. Government Securities [Member]
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total cash equivalents and marketable securities      
Basis of Fair Value Measurements, Level 3 [Member] | Municipal Securities [Member]
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total cash equivalents and marketable securities      
Basis of Fair Value Measurements, Level 3 [Member] | Commercial Paper [Member]
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Total cash equivalents and marketable securities