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Fair Value of Employee Stock Options Granted as Determined by Black-Scholes Valuation Model Assumptions (Detail) (USD $)
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12 Months Ended | ||
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Dec. 31, 2011
Year
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Dec. 31, 2010
Year
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Dec. 31, 2009
Year
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| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] | |||
| Expected dividend yield | 2.77% | 2.70% | 3.25% |
| Risk-free interest rate | 2.90% | 3.30% | 3.22% |
| Expected life in years | 7.5 | 7.5 | 7.5 |
| Expected volatility | 24.26% | 23.59% | 23.16% |
| Weighted average fair value of options granted | $ 15.92 | $ 14.83 | $ 10.86 |
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- Definition
The estimated dividend rate (a percentage of the share price) to be paid (expected dividends) to holders of the underlying shares over the option's term. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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- Definition
The period of time an equity-based award is expected to be outstanding. An equity-based award's expected term is generally determined based on, among other factors, the instrument's contractual term and the effects of employees' expected exercise and post-vesting employment termination behavior. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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- Definition
The risk-free interest rate assumption that is used in valuing an option on its own shares. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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- Definition
The range of expected volatilities used and the weighted-average expected volatility for an entity using a valuation technique with different volatilities during the contractual term. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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- Details
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- Definition
The weighted average grant-date fair value of options granted during the reporting period as calculated by applying the disclosed option pricing methodology. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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