Stock-Based Compensation - Summary of Stock Options Outstanding (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended	12 Months Ended
Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Number of Stock Options, Stock options outstanding, Beginning Balance	5,148,000
Number of Stock Options, Stock options granted	0	0
Number of Stock Options, Stock options exercised	(24,000)
Number of Stock Options, Stock options forfeited	(27,000)
Number of Stock Options, Stock options expired	(58,000)
Number of Stock Options, Stock options outstanding, Ending Balance	5,039,000		5,148,000
Number of Stock Options, Stock options vested and expected to vest	5,039,000
Number of Stock Options, Stock options exercisable	4,286,000
Weighted Avg. Exercise Price, Stock options outstanding, Beginning Balance	$ 22.65
Weighted Avg. Exercise Price, Stock options exercised	15.48
Weighted Avg. Exercise Price, Stock options forfeited	16.59
Weighted Avg. Exercise Price, Stock options expired	26.87
Weighted Avg. Exercise Price, Stock options outstanding, Ending Balance	22.66		$ 22.65
Weighted Avg. Exercise Price, Stock options vested and expected to vest	22.66
Weighted Avg. Exercise Price, Stock options exercisable	$ 23.75
Weighted Avg. Remaining Contractual Life In Years, Stock options outstanding	4 years 6 months		4 years 10 months 13 days
Weighted Avg. Remaining Contractual Life In Years, Stock options vested and expected to vest	4 years 6 months
Weighted Avg. Remaining Contractual Life In Years, Stock options exercisable	4 years
Aggregate Intrinsic Value, Stock options outstanding	$ 271		$ 6,109
Aggregate Intrinsic Value, Stock options vested and expected to vest	271
Aggregate Intrinsic Value, Stock options exercisable	$ 157

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The number of shares into which fully or partially vested stock options outstanding as of the balance sheet date can be currently converted under the option plan.

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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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Number of options or other stock instruments for which the right to exercise has lapsed under the terms of the plan agreements.

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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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Amount by which the current fair value of the underlying stock exceeds the exercise price of options outstanding.

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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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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 exercise price, at which grantee can acquire shares reserved for issuance, for 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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Weighted average price at which option holders acquired shares when converting their stock options into shares.

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Weighted average price at which grantees could have acquired the underlying shares with respect to stock options of the plan that expired.

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Weighted average price at which grantees could have acquired the underlying shares with respect to stock options that were terminated.

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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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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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Number of share options (or share units) exercised during the current period.

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