Equity Instruments - Summary of Stock-Based Compensation Expense (Detail) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized expense at June 30, 2016	$ 555,407
Weighted average remaining years to vest	9 months 29 days
Research and Development Expenses [Member] | Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expenses	$ 65,000	$ 449,000	$ 155,000	$ 1,057,000
General and Administrative Expenses [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expenses	273,000	1,641,000	943,000	2,816,000
General and Administrative Expenses [Member] | Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expenses	$ 208,000	$ 1,192,000	728,000	1,729,000
General and Administrative Expenses [Member] | Common Stock Issued for Services [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expenses			$ 60,000	$ 30,000