Fair Value Measurements - Fair Value Hierarchy for Financial Assets and Liabilities Measured on Recurring Basis (Detail) - USD ($)	Dec. 31, 2018	Dec. 31, 2017
Liabilities:
Accrued warrant liability	$ 78,637	$ 1,041,455
Recurring
Assets:
Cash and cash equivalents	1,130	551,088
Short-term investments	503,810	4,561,357
Assets:	504,940	5,112,445
Recurring | Level 1
Assets:
Cash and cash equivalents	1,130	551,088
Short-term investments	0	3,606,499
Assets:	1,130	4,157,587
Recurring | Level 2
Assets:
Cash and cash equivalents	0	0
Short-term investments	503,810	954,858
Assets:	503,810	954,858
Recurring | Level 3
Assets:
Cash and cash equivalents	0	0
Short-term investments	0	0
Assets:	0	0
Warrants | Recurring
Liabilities:
Accrued warrant liability	78,637	1,041,455
Warrants | Recurring | Level 1
Liabilities:
Accrued warrant liability	0	0
Warrants | Recurring | Level 2
Liabilities:
Accrued warrant liability	0	0
Warrants | Recurring | Level 3
Liabilities:
Accrued warrant liability	$ 78,637	$ 1,041,455