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Key Assumptions Used to Estimate Fair Value of Stock Options Granted (Detail) (Stock options)
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3 Months Ended | |
|---|---|---|
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Mar. 31, 2015
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Mar. 31, 2014
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| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] | ||
| Risk-free interest rate | 1.50% | |
| Expected life of the options (years) | 5 years | 5 years |
| Expected stock price volatility | 38.40% | |
| Expected dividend rate | 1.60% | |
| Minimum | ||
| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] | ||
| Risk-free interest rate | 1.30% | |
| Expected stock price volatility | 35.60% | |
| Expected dividend rate | 1.80% | |
| Maximum | ||
| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] | ||
| Risk-free interest rate | 1.50% | |
| Expected stock price volatility | 35.70% | |
| Expected dividend rate | 2.00% | |