Stockholders' Equity - Summary of Stock Option Outstanding (Detail) - $ / shares	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Equity [Abstract]
Option Outstanding - Range of Exercise Prices, Lower Limit	$ 0.78	$ 1.45
Option Outstanding - Range of Exercise Prices, Upper Limit	$ 3.75	$ 3.75
Option Outstanding - Number of Shares	5,943,908	5,006,532	4,141,948
Option Outstanding - Weighted-Average Remaining Contractual Life	6 years 9 months 18 days	6 years 6 months
Option Outstanding - Weighted Average Exercise Price	$ 2.04	$ 2.66	$ 2.48
Option Exercisable	3,643,718	3,301,532
Option Exercisable - Weighted Average Exercise Price	$ 2.44	$ 2.58