Income Taxes - Summary of Deferred Tax Assets (Detail) - USD ($)	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Estimated net operating loss carryforward	$ 3,355,180	$ 2,218,618
Estimated research and development credits	2,686,666	2,244,047
Accruals and other	2,560,417	2,273,838
Deferred rent	90,866	164,821
Gross deferred tax assets	8,693,129	6,901,324
Less valuation allowance	$ (8,693,129)	$ (6,901,324)

Amount before allocation of valuation allowances of deferred tax asset attributable to deductible temporary differences and carryforwards.

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Amount before allocation of valuation allowances of deferred tax asset attributable to deductible temporary differences from in-process research and development costs expensed in connection with a business combination.

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Amount before allocation of valuation allowances of deferred tax asset attributable to deductible operating loss carryforwards.

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Amount before allocation of valuation allowances of deferred tax asset attributable to deductible temporary differences from deferred rent.

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Amount of deferred tax assets for which it is more likely than not that a tax benefit will not be realized.

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