Share-Based Compensation - Activity in Company's Plan (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	6 Months Ended
Jun. 30, 2013
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Outstanding at January 1, 2013, Number of Shares	32,150
Granted, Number of Shares	0
Exercised, Number of Shares	(10,900)
Forfeited, Number of Shares	0
Outstanding (vested and expected to vest) at June 30, 2013, Number of Shares	21,250
Exercisable at June 30, 2013, Number of Shares	21,250
Outstanding at January 1, 2013, Weighted Average Exercise Price per Share	$ 40.93
Granted, Weighted Average Exercise Price per Share	$ 0.00
Exercised, Weighted Average Exercise Price per Share	$ 41.50
Forfeited, Weighted Average Exercise Price per Share	$ 0.00
Outstanding (vested and expected to vest) at June 30, 2013, Weighted Average Exercise Price per Share	$ 40.63
Exercisable at June 30, 2013, Weighted Average Exercise Price per Share	$ 40.63
Outstanding (vested and expected to vest), Weighted Average Remaining Contractual Term	3 years 9 months 18 days
Exercisable, Weighted Average Remaining Contractual Term	3 years 9 months 18 days
Outstanding (vested and expected to vest), Aggregate Intrinsic Value	$ 546
Exercisable, Aggregate Intrinsic Value	$ 546

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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 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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-Name Accounting Standards Codification

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-Section 50

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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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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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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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Amount by which the current fair value of the underlying stock exceeds the exercise price of fully vested and expected to vest options outstanding.

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As of the balance sheet date, the number of shares into which fully vested and expected to vest stock options outstanding can be converted under the option plan.

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As of the balance sheet date, the weighted-average exercise price for outstanding stock options that are fully vested or expected to vest.

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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 the reported fact of one year, five months, and thirteen days.

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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 that were terminated.

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

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