Quarterly report pursuant to Section 13 or 15(d)

Commitments and Contingencies - Additional Information (Detail)

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Commitments and Contingencies - Additional Information (Detail) - Office Space and Research Facilities Lease - USD ($)
3 Months Ended 9 Months Ended
Sep. 30, 2018
Sep. 30, 2017
Sep. 30, 2018
Sep. 30, 2017
Commitment And Contingencies [Line Items]        
Operating leases, rent expense $ 220,081 $ 223,866 $ 687,113 $ 615,176
Lease agreement description     The 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     Feb. 28, 2022  
Maximum        
Commitment And Contingencies [Line Items]        
Payments for tenant improvements allowance     $ 515,000