Summarized Quarterly Data (Unaudited) - Summarized Quarterly Data (Detail) - USD ($)	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016
Quarterly Financial Information Disclosure [Abstract]
Research and development expense	$ 1,631,540	$ 2,717,698	$ 2,017,569	$ 770,686	$ 1,502,032	$ 1,339,343	$ 2,095,149	$ 2,015,076	$ 7,137,493	$ 6,951,600
General and administrative expense	1,027,594	984,047	871,979	1,209,570	822,325	830,092	802,655	1,137,753	4,093,189	3,592,825
Change in fair value of warrant liability	(2,349,624)	1,544,138	(1,261,912)	3,072,747	(796,560)	198,945			1,005,349	(597,615)
Net loss	$ (308,443)	$ (5,243,061)	$ (1,625,969)	$ (5,052,039)	$ (1,527,343)	$ (3,025,281)	$ (2,970,498)	$ (3,225,409)	$ (12,229,512)	$ (10,748,531)
Net loss per common share, basic	$ (0.02)	$ (0.34)	$ (0.11)	$ (0.37)					$ (0.82)	$ (1.15)
Net loss per common share, diluted	$ (0.07)	$ (0.34)	$ (0.13)	$ (0.37)					$ (0.90)	$ (1.15)
Weighted average shares outstanding, basic	15,368,610	15,351,295	15,343,325	13,528,311					14,897,885	9,338,068
Weighted average shares outstanding, diluted	15,503,583	15,351,295	15,420,954	13,528,311					14,951,036	9,338,068
Net loss per common share, basic and diluted					$ (0.12)	$ (0.29)	$ (0.41)	$ (0.45)
Weighted average shares outstanding, basic and diluted					12,305,360	10,614,692	7,217,577	7,168,005