Stock-Based Compensation - Summary of Stock Options Outstanding by Exercise Price Range (Detail) - $ / shares	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Options Outstanding, Number of Options	11,900,671
Options Outstanding, Weighted Average Exercise Price (in dollars per share)	$ 4.20
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Remaining Contractual Term	7 years 8 months 12 days	7 years 8 months 12 days
Options Vested and Exercisable, Number of Options	4,260,008
Options Vested and Exercisable, Weighted Average Exercise Price (in dollars per share)	$ 6.43
Options Vested and Exercisable, Weighted Average Remaining Contractual Term	6 years 6 months
$0.044 to 2.35
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Range of Exercise Prices, lower limit (in dollars per share)	$ 0.044
Range of Exercise Prices, upper limit (in dollars per share)	$ 2.35
Options Outstanding, Number of Options	1,268,956
Options Outstanding, Weighted Average Exercise Price (in dollars per share)	$ 1.73
Options Outstanding, Weighted Average Remaining Contractual Term	4 years 2 months
Options Vested and Exercisable, Number of Options	1,180,523
Options Vested and Exercisable, Weighted Average Exercise Price (in dollars per share)	$ 1.69
Options Vested and Exercisable, Weighted Average Remaining Contractual Term	3 years 11 months
$2.46 to 2.54
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Range of Exercise Prices, lower limit (in dollars per share)	$ 2.46
Range of Exercise Prices, upper limit (in dollars per share)	$ 2.54
Options Outstanding, Number of Options	3,108,991
Options Outstanding, Weighted Average Exercise Price (in dollars per share)	$ 2.47
Options Outstanding, Weighted Average Remaining Contractual Term	8 years 11 months
Options Vested and Exercisable, Number of Options	691,191
Options Vested and Exercisable, Weighted Average Exercise Price (in dollars per share)	$ 2.47
Options Vested and Exercisable, Weighted Average Remaining Contractual Term	8 years 7 months
$2.58 to 3.60
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Range of Exercise Prices, lower limit (in dollars per share)	$ 2.58
Range of Exercise Prices, upper limit (in dollars per share)	$ 3.6
Options Outstanding, Number of Options	4,965,565
Options Outstanding, Weighted Average Exercise Price (in dollars per share)	$ 2.70
Options Outstanding, Weighted Average Remaining Contractual Term	8 years 3 months
Options Vested and Exercisable, Number of Options	186,560
Options Vested and Exercisable, Weighted Average Exercise Price (in dollars per share)	$ 3.06
Options Vested and Exercisable, Weighted Average Remaining Contractual Term	9 years 4 months
$6.79 to 9.72
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Range of Exercise Prices, lower limit (in dollars per share)	$ 6.79
Range of Exercise Prices, upper limit (in dollars per share)	$ 9.72
Options Outstanding, Number of Options	1,173,475
Options Outstanding, Weighted Average Exercise Price (in dollars per share)	$ 8.12
Options Outstanding, Weighted Average Remaining Contractual Term	6 years 6 months
Options Vested and Exercisable, Number of Options	990,176
Options Vested and Exercisable, Weighted Average Exercise Price (in dollars per share)	$ 8.12
Options Vested and Exercisable, Weighted Average Remaining Contractual Term	6 years 2 months
$10.56 to 27.03
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Range of Exercise Prices, lower limit (in dollars per share)	$ 10.56
Range of Exercise Prices, upper limit (in dollars per share)	$ 27.03
Options Outstanding, Number of Options	1,383,684
Options Outstanding, Weighted Average Exercise Price (in dollars per share)	$ 12.41
Options Outstanding, Weighted Average Remaining Contractual Term	7 years 1 month
Options Vested and Exercisable, Number of Options	1,211,558
Options Vested and Exercisable, Weighted Average Exercise Price (in dollars per share)	$ 12.46
Options Vested and Exercisable, Weighted Average Remaining Contractual Term	7 years