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Summary of Significant Accounting Policies - Additional Information (Detail) (USD $)
12 Months Ended
Dec. 31, 2012
Dec. 31, 2011
Significant Accounting Policies [Line Items]    
Security deposit for leased office space $ 6,000  
Estimated useful lives of intangible assets 5 years  
Amortization expense of intangible assets 6,000 3,000
Gross intangible assets 78,000 78,000
Accumulated amortization of intangible assets 48,000 42,000
Fair Value, Inputs, Level 2 | Money market funds
   
Significant Accounting Policies [Line Items]    
Money market funds $ 583,000 $ 6,123,000
Computer and office equipment
   
Significant Accounting Policies [Line Items]    
Estimated useful lives of property and equipment 3 years  
Furniture and fixtures
   
Significant Accounting Policies [Line Items]    
Estimated useful lives of property and equipment 5 years