Stock-Based Compensation - Summary of Stock Option Activity (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended	12 Months Ended
	Mar. 31, 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	2,810
Number of Shares, Exercised	(521)
Number of Shares, Forfeited	(153)
Number of Shares, Outstanding, Ending balance	22,243	20,107
Number of shares vested and expected to vest	21,798
Number of stock option exercisable	15,769
Weighted Average Exercise Price, Outstanding, Beginning balance	$ 3.93
Weighted Average Exercise Price, Granted	$ 5.02
Weighted Average Exercise Price, Exercised	$ 2.06
Weighted Average Exercise Price, Forfeited	$ 6.11
Weighted Average Exercise Price, Outstanding, Ending balance	$ 4.09	$ 3.93
Weighted average exercise price of shares vested and expected to vest (in dollars per share)	$ 4.06
Weighted average exercise price for exercisable option (in dollars per share)	$ 3.36
Remaining Contractual Term	6 years 4 months 28 days	6 years 1 month 10 days
Remaining Contractual Term, Vested and expected to vest	6 years 4 months 6 days
Remaining Contractual Term, Exercisable	5 years 3 months 7 days
Aggregate Intrinsic Value, Outstanding, Beginning balance	$ 38,348
Aggregate Intrinsic Value, Outstanding, Ending balance	33,398	38,348
Aggregate Intrinsic Value, Vested and expected to vest	33,365
Aggregate Intrinsic Value, Exercisable	$ 32,975