Stock-Based Compensation - Stock-Based Compensation Expense (Detail) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation expense and effect on net loss	$ 1,351,574	$ 513,660	$ 2,660,468	$ 1,034,766
Effect on basic and diluted net loss per share	$ (0.01)	$ (0.01)	$ (0.03)	$ (0.02)
Research and development expense [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation expense and effect on net loss	$ 698,039	$ 39,596	$ 1,281,708	$ 225,889
Selling, general and administrative expense [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation expense and effect on net loss	$ 653,535	$ 474,064	$ 1,378,760	$ 808,877