Annual report pursuant to Section 13 and 15(d)

Financial Instruments - Financial Instruments Measured on Recurring Basis (Detail)

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Financial Instruments - Financial Instruments Measured on Recurring Basis (Detail) (USD $)
In Thousands, unless otherwise specified
Dec. 31, 2012
Dec. 31, 2011
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Fair value of financial instruments $ 60,089 $ 72,082
Fair Value Measurements Recurring [Member]
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Fair value of financial instruments 60,089 72,082
Fair Value Measurements Recurring [Member] | Government debt securities [Member]
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Fair value of financial instruments 6,003 15,969
Fair Value Measurements Recurring [Member] | Corporate debt securities [Member]
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Fair value of financial instruments 49,443 41,741
Money market funds [Member]
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Fair value of financial instruments 4,643 14,372
Money market funds [Member] | Fair Value Measurements Recurring [Member]
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Fair value of financial instruments 4,643 14,372
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Fair Value Measurements Recurring [Member]
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Fair value of financial instruments 4,643 14,372
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Money market funds [Member] | Fair Value Measurements Recurring [Member]
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Fair value of financial instruments 4,643 14,372
Significant Other Observable Inputs (Level 2) [Member] | Fair Value Measurements Recurring [Member]
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Fair value of financial instruments 55,446 57,710
Significant Other Observable Inputs (Level 2) [Member] | Fair Value Measurements Recurring [Member] | Government debt securities [Member]
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Fair value of financial instruments 6,003 15,969
Significant Other Observable Inputs (Level 2) [Member] | Fair Value Measurements Recurring [Member] | Corporate debt securities [Member]
   
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Fair value of financial instruments $ 49,443 $ 41,741