Equity Compensation - Stock Options Granted and Exercised (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended
Mar. 31, 2013	Mar. 31, 2012
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Shares subject to stock options granted	0	156,500
Weighted average grant date fair value per share	$ 0.00	$ 31.36
Shares subject to stock options exercised	0	104,054
Intrinsic value of stock options exercised	$ 0	$ 2,489
Proceeds received from stock options exercised	0	4,668
Tax benefits realized from stock options exercised	$ 0	$ 864

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Aggregate proceeds received by the entity during the annual period from exercises of stock or unit options and conversion of similar instruments granted under equity-based payment arrangements.

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Disclosure of the aggregate tax benefit realized from the exercise of stock options and the conversion of similar instruments during the annual period.

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

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