Stock-Based Compensation - Summary of Stock Option Activity and Related Information (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	6 Months Ended
Jun. 30, 2013
Options Outstanding
Beginning balance	5,390,582
Granted	25,000
Exercised	(32,284)
Forfeited	(74,437)
Ending balance	5,308,861
Vested and expected to vest	5,142,695
Exercisable	3,540,828
Weighted-Average Exercise Price per Share
Beginning balance	$ 5.18
Granted	$ 5.30
Exercised	$ 1.31
Forfeited	$ 7.45
Ending balance	$ 5.18
Vested and expected to vest	$ 5.09
Exercisable	$ 3.87
Weighted- Average Remaining Contractual Life
Balance	6 years 9 months 3 days
Vested and expected to vest	6 years 8 months 12 days
Exercisable	5 years 9 months
Aggregate Intrinsic Value
Balance	$ 7,650
Vested and expected to vest	7,604
Exercisable	$ 7,191

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Amount of difference between fair value of the underlying shares reserved for issuance and exercise price of vested portions of options outstanding and currently exercisable.

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The number of shares reserved for issuance under stock option agreements awarded under the plan that validly exist and are outstanding as of the balance sheet date, including vested options.

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Weighted average remaining contractual term for option awards outstanding, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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