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Fair Value Hierarchy for Financial Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) (Fair Value, Measurements, Recurring, USD $)
In Thousands, unless otherwise specified
Dec. 31, 2013
Dec. 31, 2012
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]    
Assets $ 187,610 $ 123,588
Fair Value, Inputs, Level 1
    
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]    
Assets 20,013 3,140
Fair Value, Inputs, Level 2
    
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]    
Assets 167,597 120,448
Money market funds
    
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]    
Assets 20,013 3,140
Money market funds | Fair Value, Inputs, Level 1
    
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]    
Assets 20,013 3,140
US Government Agencies Debt Securities
    
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]    
Assets 167,597 119,233
US Government Agencies Debt Securities | Fair Value, Inputs, Level 2
    
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]    
Assets 167,597 119,233
US Treasury Securities
    
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]    
Assets   500
US Treasury Securities | Fair Value, Inputs, Level 2
    
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]    
Assets   500
Municipal Securities
    
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]    
Assets   715
Municipal Securities | Fair Value, Inputs, Level 2
    
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]    
Assets   $ 715