Summarized Quarterly Data (Unaudited) - Summarized Quarterly Data (Detail) - USD ($)	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017
Quarterly Financial Information Disclosure [Abstract]
Research and development expense	$ 695,360	$ 625,497	$ 1,388,791	$ 1,385,366	$ 1,631,540	$ 2,717,698	$ 2,017,569	$ 770,686	$ 4,095,014	$ 7,137,493
General and administrative expense	1,073,061	897,060	917,305	1,032,245	1,027,594	984,047	871,979	1,209,570	3,919,671	4,093,189
Gain (loss) from change in fair value of warrant liability				433,392	2,349,624	(1,544,138)	1,261,912	(3,072,747)	433,392	(1,005,349)
Net loss	$ (1,760,633)	$ (1,519,468)	$ (2,303,193)	$ (1,982,786)	$ (308,443)	$ (5,243,061)	$ (1,625,969)	$ (5,052,039)	$ (7,566,080)	$ (12,229,512)
Net loss per common share, basic and diluted	$ (0.10)	$ (0.09)	$ (0.14)	$ (0.13)
Weighted average shares outstanding, basic and diluted	17,427,533	17,129,649	16,425,468	15,427,037
Net loss per share of common stock, basic					$ (0.02)	$ (0.34)	$ (0.11)	$ (0.37)	$ (0.46)	$ (0.82)
Net loss per share of common stock, diluted					$ (0.07)	$ (0.34)	$ (0.13)	$ (0.37)	$ (0.46)	$ (0.90)
Weighted average shares outstanding, basic					15,368,610	15,351,295	15,343,325	13,528,311	16,602,422	14,897,885
Weighted average shares outstanding, diluted					15,503,583	15,351,295	15,420,954	13,528,311	16,602,422	14,951,036