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Commitments and Contingencies - Additional Information (Detail) - USD ($)
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Chief Executive Officer        
Commitment And Contingencies [Line Items]        
Contingent Severance cost       $ 575,000
Severance cost, description These agreements provide severance in the aggregate amount of $575,000 for termination without cause as defined in the agreements.      
Office Space and Research Facilities Lease        
Commitment And Contingencies [Line Items]        
Operating leases, rent expense $ 805,271 $ 672,526 $ 742,829  
Lease agreement description The new San Diego facility lease agreement included a tenant improvement allowance which provided for the landlord to pay for tenant improvements on behalf of the Company up to $515,000. Based on the terms of this landlord incentive and involvement of the Company in the construction process, the leasehold improvements purchased under the landlord incentive were determined to be property of the Company.      
Lease expiration date Dec. 31, 2020      
Office Space and Research Facilities Lease | Maximum        
Commitment And Contingencies [Line Items]        
Payments for tenant improvements allowance $ 515,000