Equity Incentive Plans - Summary of Stock Option Activities (Detail) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Outstanding Beginning Balance, Number of Options	3,428,665	3,179,899	3,215,945
Granted, Number of Options	70,865	827,406	802,193
Forfeited, Number of Options	(88,443)	(282,537)	(325,765)
Exercised, Number of Options	(539,183)	(296,103)	(512,474)
Outstanding Ending Balance, Number of Options	2,871,904	3,428,665	3,179,899	3,215,945
Vested and expected to vest, Number of Options	2,865,475	3,389,763	3,155,828
Exercisable, Number of Options	2,395,979	2,531,243	2,547,902
Outstanding Beginning Balance, Weighted Average Exercise Price of Stock Options	$ 9.23	$ 9.61	$ 9.60
Granted, Weighted Average Exercise Price of Stock Options	10.43	6.04	7.92
Forfeited, Weighted Average Exercise Price of Stock Options	12.77	7.67	9.88
Exercised, Weighted Average Exercise Price of Stock Options	6.94	5.85	6.70
Outstanding Ending Balance, Weighted Average Exercise Price of Stock Options	9.59	9.23	9.61	$ 9.60
Vested and expected to vest, Weighted Average Exercise Price of Stock Options	9.59	9.27	9.62
Exercisable, Weighted Average Exercise Price of Stock Options	$ 10.11	$ 10.11	$ 9.63
Outstanding Beginning Balance, Aggregate Intrinsic Value of Stock Options	$ 525		$ 39,615
Exercised, Aggregate Intrinsic Value of Stock Options	1,540	$ 806	$ 692
Outstanding Ending Balance, Aggregate Intrinsic Value of Stock Options	6,073	525		$ 39,615
Vested and expected to vest, Aggregate Intrinsic Value of Stock Options	6,050	508
Exercisable, Aggregate Intrinsic Value of Stock Options	$ 4,603	$ 236
Outstanding, Weighted Average Remaining Contractual Life of Stock Options	6 years 2 months 12 days	6 years 8 months 12 days	6 years 8 months 12 days	6 years 7 months 6 days
Vested and expected to vest, Weighted Average Remaining Contractual Life of Stock Options	6 years 2 months 12 days	6 years 8 months 12 days	6 years 8 months 12 days
Exercisable, Weighted Average Remaining Contractual Life of Stock Options	5 years 8 months 12 days	5 years 10 months 25 days	6 years
Outstanding, Weighted Average Remaining Contractual Life of Stock Options	6 years 2 months 12 days	6 years 8 months 12 days	6 years 8 months 12 days	6 years 7 months 6 days

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The weighted-average price as of the balance sheet date at which grantees can acquire the shares reserved for issuance on vested portions of options outstanding and currently exercisable under the stock option plan.

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The number of shares under options that were cancelled during the reporting period as a result of occurrence of a terminating event specified in contractual agreements pertaining to the stock option plan.

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Gross number of share options (or share units) granted during the period.

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Number of options outstanding, including both vested and non-vested options.

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Weighted average price at which grantees can acquire the shares reserved for issuance under the stock option plan.

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Number of fully vested and expected to vest exercisable options that may be converted into shares under option plan. Includes, but is not limited to, unvested options for which requisite service period has not been rendered but that are expected to vest based on achievement of performance condition, if forfeitures are recognized when they occur.

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Amount by which current fair value of underlying stock exceeds exercise price of fully vested and expected to vest options outstanding. Includes, but is not limited to, unvested options for which requisite service period has not been rendered but that are expected to vest based on achievement of performance condition, if forfeitures are recognized when they occur.

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Number of fully vested and expected to vest options outstanding that can be converted into shares under option plan. Includes, but is not limited to, unvested options for which requisite service period has not been rendered but that are expected to vest based on achievement of performance condition, if forfeitures are recognized when they occur.

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Weighted average price at which option holders acquired shares when converting their stock options into shares.

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Weighted average per share amount at which grantees can acquire shares of common stock by exercise of options.

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Weighted average remaining contractual term for vested portions of options outstanding and currently exercisable or convertible, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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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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Weighted average remaining contractual term for fully vested and expected to vest options outstanding, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days. Includes, but is not limited to, unvested options for which requisite service period has not been rendered but that are expected to vest based on achievement of performance condition, if forfeitures are recognized when they occur.

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