Stockholders' Equity - Summary of Activity Related to Options Granted (Detail) - USD ($)	9 Months Ended	12 Months Ended
	Sep. 30, 2015	Dec. 31, 2014	Dec. 31, 2013
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Number of stock options outstanding, beginning balance	3,144,993	4,045,324
Number of stock options granted		252,000
Number of stock options exercised	(218,010)	(1,138,331)
Number of stock options forfeited		(14,000)
Number of stock options expired	566,983
Number of stock options outstanding, ending balance	2,360,000	3,144,993	4,045,324
Number of stock options exercisable	2,152,667
Weighted average exercise price, options outstanding, beginning balance	$ 2.39	$ 1.85
Number of stock options unvested ending balance	207,333
Weighted average exercise price, options granted		3.80
Weighted average exercise price, options exercised	$ 1.50	0.78
Weighted average exercise price, options forfeited		2.43
Weighted average exercise price, options expired	1.54
Weighted average exercise price, options outstanding, ending balance	$ 2.67	$ 2.39	$ 1.85
Aggregate fair value, beginning balance	$ 7,516,533	$ 7,483,849
Weighted average exercise price, options exercisable	$ 2.61
Aggregate fair value, ending balance	$ 6,301,200	$ 7,516,533	$ 7,483,849
Weighted average remaining contractual term, options outstanding	6 months 26 days	1 year 5 months 23 days	2 years 18 days
Aggregate fair value, exercisable	$ 5,618,461