Summarized Quarterly Data - Summarized Quarterly Data (Detail) - USD ($)	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014
Quarterly Financial Information Disclosure [Abstract]
Research and development expense	$ 1,708,302	$ 1,837,743	$ 2,188,138	$ 2,419,961	$ 2,176,388	$ 3,088,373	$ 2,874,977	$ 1,852,116	$ 8,154,144	$ 9,991,855
General and administrative expense	842,777	819,703	976,418	1,025,261	738,012	732,800	616,888	1,070,479	3,664,159	3,158,179
Net loss	$ (2,624,152)	$ (2,735,400)	$ (3,241,163)	$ (3,520,748)	$ (2,919,803)	$ (3,825,354)	$ (3,547,040)	$ (2,955,484)	$ (12,121,463)	$ (13,247,681)
Net loss per common share, basic and diluted	$ (0.37)	$ (0.42)	$ (0.52)	$ (0.58)	$ (0.48)	$ (0.63)	$ (0.59)	$ (0.49)	$ (1.87)	$ (2.20)
Weighted average shares outstanding, basic and diluted	7,123,163	6,494,845	6,212,803	6,103,783	6,065,841	6,054,250	6,027,672	6,002,936	6,485,794	6,032,560