Share-Based Compensation Plans (Summary of Stock Option Activity) (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
Dec. 31, 2018	Dec. 31, 2016
Stock option
Balance at December 31, 2017	66
Exercised during 2018	(36)	0
Balance at December 31, 2018	30
Exercisable at December 31, 2018	30
Stock option, weighted-average exercise price
Balance at December 31, 2017	$ 27.66
Exercised during 2018	27.66
Balance at December 31, 2018	27.66
Exercisable at December 31, 2018	$ 27.66
Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures
Ending Balance, Weighted-average remaining contractual term, years	5 years
Exercisable at December 31, 2018, Weighted-average remaining contractual term, years	5 years
Ending Balance, Aggregate intrinsic value	$ 509
Exercisable at December 31, 2018, Aggregate intrinsic value	$ 509

No definition available.

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- Definition

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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- Definition

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

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- Definition

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

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- Definition

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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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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- Definition

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

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

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