Stock-Based Compensation - Summary of Stock Option Activity (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	6 Months Ended	12 Months Ended
	Jun. 30, 2014	Dec. 31, 2013
Share Based Compensation Arrangement By Share Based Payment Award Options Outstanding [Roll Forward]
Number of Shares, Outstanding, Beginning balance	20,107
Number of Shares, Granted	3,107
Number of Shares, Exercised	(1,653)
Number of Shares, Forfeited	(316)
Number of Shares, Outstanding, Ending balance	21,245	20,107
Number of shares vested and expected to vest	20,889
Number of stock option exercisable	15,759
Weighted Average Exercise Price, Outstanding, Beginning balance	$ 3.93
Weighted Average Exercise Price, Granted	$ 5.17
Weighted Average Exercise Price, Exercised	$ 2.34
Weighted Average Exercise Price, Forfeited	$ 6.27
Weighted Average Exercise Price, Outstanding, Ending balance	$ 4.20	$ 3.93
Weighted average exercise price of shares vested and expected to vest (in dollars per share)	$ 4.17
Weighted average exercise price for exercisable option (in dollars per share)	$ 3.62
Weighted Average Remaining Contractual Term	6 years 3 months 15 days	6 years 1 month 10 days
Weighted Average Remaining Contractual Term, Vested and expected to vest	6 years 2 months 27 days
Weighted Average Remaining Contractual Term, Exercisable	5 years 4 months 6 days
Aggregate Intrinsic Value, Outstanding, Beginning balance	$ 38,348
Aggregate Intrinsic Value, Outstanding, Ending balance	66,353	38,348
Aggregate Intrinsic Value, Vested and expected to vest	65,734
Aggregate Intrinsic Value, Exercisable	$ 58,220