Summary of Share Option Activity (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	9 Months Ended
Sep. 30, 2013	Sep. 30, 2012
Number of Common Shares
Balance at January 1, 2013	440,453
Granted	20,229
Exercised	(10,964)	(1,217)
Forfeited or expired	(4,962)
Balance at September 30, 2013	444,756
Exercisable at June 30, 2013	399,221
Weighted Average Exercise Share Price
Balance at January 1, 2013	$ 29.17
Granted	$ 20.26
Exercised	$ 12.70
Forfeited or expired	$ 34.29
Balance at September 30, 2013	$ 29.11
Exercisable at September 30, 2013	$ 30.21
Weighted average fair value of options granted during the year	$ 7.99	$ 7.85
Weighted Average Contractual Remaining Life(Years)
Balance at end of period	1 year 10 months 24 days
Exercisable at end of period	1 year 6 months
Aggregate Intrinsic Value
Balance at January 1, 2013	$ 557
Granted	0
Exercised	0
Forfeited or expired	0
Balance at June 30, 2013	1,032
Exercisable at June 30, 2013	$ 861

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Share Based Compensation Arrangement By Share Based Payment Award Options Forfeitures and Expirations In Period Total Intrinsic Value

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Share Based Compensation Arrangement By Share Based Payment Award Options Grants In Period Intrinsic Value

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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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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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Amount of accumulated difference between fair value of underlying shares on dates of exercise and exercise price on options exercised (or share units converted) into shares.

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For presentations that combine terminations, 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 or that expired.

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Weighted average price of options that were either forfeited or expired.

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

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The weighted average grant-date fair value of options granted during the reporting period as calculated by applying the disclosed option pricing methodology.

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

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