Equity - Additional Information (Detail) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015	Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock option outstanding	5,215,862		5,215,862		5,326,505
Stock options, granted			2,542,527
Unrecognized stock-based compensation cost	$ 8,200,000		$ 8,200,000
Unrecognized share-based compensation expense, weighted-average recognition period			1 year 6 months
Stock compensation expense (gain)	1,686,000	$ 828,000	$ 4,034,000	$ 1,734,000
Research And Development Expense [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock compensation expense (gain)	187,000	161,000	550,000	339,000
Research And Development Expense [Member] | Warrant [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock compensation expense (gain)	$ 0	$ 58,000	$ (10,075)	$ 173,000
Non-Employees [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock options, granted			1,005,000
Stock option vested			117,500
Stock option unvested	887,500		887,500
Unrecognized stock-based compensation cost	$ 2,200,000		$ 2,200,000