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Fair Value of Financial Instruments (Details) (USD $)
 9 Months Ended
Sep. 30, 2014
Dec. 31, 2013
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Fair Value, Assets, Level 2 to Level 1 Transfers, Amount $ 0  
Fair Value, Assets, Level 1 to Level 2 Transfers, Amount 0  
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Transfers Into Level 3 0  
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers out of Level 3 0  
Assets, Fair Value Disclosure [Abstract]    
Cash and Cash Equivalents, Fair Value Disclosure 16,184,000 39,652,000
AFS Securities, Fair Value Disclosure 100,647,000 88,024,000
Fair Value, Measurements, Recurring | Level 1
    
Assets, Fair Value Disclosure [Abstract]    
Total assets measured at fair value 6,775,000 22,991,000
Fair Value, Measurements, Recurring | Level 2
    
Assets, Fair Value Disclosure [Abstract]    
Total assets measured at fair value 100,647,000 89,234,000
Fair Value, Measurements, Recurring | Total
    
Assets, Fair Value Disclosure [Abstract]    
Total assets measured at fair value 107,422,000 112,225,000
Fair Value, Measurements, Recurring | Money market funds | Level 1
    
Assets, Fair Value Disclosure [Abstract]    
Cash and Cash Equivalents, Fair Value Disclosure 6,775,000 22,991,000
Fair Value, Measurements, Recurring | Money market funds | Level 2
    
Assets, Fair Value Disclosure [Abstract]    
Cash and Cash Equivalents, Fair Value Disclosure 0 0
Fair Value, Measurements, Recurring | Money market funds | Total
    
Assets, Fair Value Disclosure [Abstract]    
Cash and Cash Equivalents, Fair Value Disclosure 6,775,000 22,991,000
Fair Value, Measurements, Recurring | Commercial paper | Level 1
    
Assets, Fair Value Disclosure [Abstract]    
AFS Securities, Fair Value Disclosure 0 0
Fair Value, Measurements, Recurring | Commercial paper | Level 2
    
Assets, Fair Value Disclosure [Abstract]    
AFS Securities, Fair Value Disclosure 1,599,000 900,000
Fair Value, Measurements, Recurring | Commercial paper | Total
    
Assets, Fair Value Disclosure [Abstract]    
AFS Securities, Fair Value Disclosure 1,599,000 900,000
Fair Value, Measurements, Recurring | U.S. government agency securities | Level 1
    
Assets, Fair Value Disclosure [Abstract]    
AFS Securities, Fair Value Disclosure 0 0
Fair Value, Measurements, Recurring | U.S. government agency securities | Level 2
    
Assets, Fair Value Disclosure [Abstract]    
AFS Securities, Fair Value Disclosure 8,505,000 11,279,000
Fair Value, Measurements, Recurring | U.S. government agency securities | Total
    
Assets, Fair Value Disclosure [Abstract]    
AFS Securities, Fair Value Disclosure 8,505,000 11,279,000
Fair Value, Measurements, Recurring | U.S. Treasury securities | Level 1
    
Assets, Fair Value Disclosure [Abstract]    
AFS Securities, Fair Value Disclosure 0 0
Fair Value, Measurements, Recurring | U.S. Treasury securities | Level 2
    
Assets, Fair Value Disclosure [Abstract]    
AFS Securities, Fair Value Disclosure 3,554,000 5,235,000
Fair Value, Measurements, Recurring | U.S. Treasury securities | Total
    
Assets, Fair Value Disclosure [Abstract]    
AFS Securities, Fair Value Disclosure 3,554,000 5,235,000
Fair Value, Measurements, Recurring | Municipal debt securities | Level 1
    
Assets, Fair Value Disclosure [Abstract]    
AFS Securities, Fair Value Disclosure 0 0
Fair Value, Measurements, Recurring | Municipal debt securities | Level 2
    
Assets, Fair Value Disclosure [Abstract]    
AFS Securities, Fair Value Disclosure 3,948,000 4,765,000
Fair Value, Measurements, Recurring | Municipal debt securities | Total
    
Assets, Fair Value Disclosure [Abstract]    
AFS Securities, Fair Value Disclosure 3,948,000 4,765,000
Fair Value, Measurements, Recurring | Corporate debt securities | Level 1
    
Assets, Fair Value Disclosure [Abstract]    
AFS Securities, Fair Value Disclosure 0 0
Fair Value, Measurements, Recurring | Corporate debt securities | Level 2
    
Assets, Fair Value Disclosure [Abstract]    
AFS Securities, Fair Value Disclosure 83,041,000 67,055,000
Fair Value, Measurements, Recurring | Corporate debt securities | Total
    
Assets, Fair Value Disclosure [Abstract]    
AFS Securities, Fair Value Disclosure $ 83,041,000 $ 67,055,000