Income Taxes - Schedule of Gross Deferred Tax Asset and Related Valuation Allowance (Detail) - USD ($)	Dec. 31, 2016	Dec. 31, 2015
Deferred tax assets:
Net operating loss carryforward	$ 34,451,814	$ 24,745,536
Capitalized start-up costs	2,708,479	2,986,272
Patent amortization	216,203	238,378
Research and orphan drug credits	14,988,522	10,110,590
Deferred rent	123,744	96,107
Deferred compensation	2,107,964	1,206,920
Other	70,511	52,985
Total gross deferred tax assets	54,667,237	39,436,788
Valuation allowance	$ (54,667,237)	$ (39,436,788)

Deferred tax assets capitalized start up costs.

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Deferred tax assets patent amortization.

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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 allowance, of deferred tax asset attributable to deductible temporary differences, classified as other.

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Amount before allocation of valuation allowances of deferred tax asset attributable to deductible temporary differences from compensation and benefits costs.

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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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