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Assumptions Used to Estimate Weighted Average Fair Value of Options (Detail)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted-average volatility	49.00%	50.00%	49.00%
Expected dividend yield	1.90%	2.20%	2.00%
Expected term (in years)	4 years 5 months	4 years 7 months 6 days	4 years 8 months 12 days
Weighted average risk free interest rate	0.90%	0.70%	1.40%

The estimated measure of the percentage by which a share price is expected to fluctuate during a period. Volatility also may be defined as a probability-weighted measure of the dispersion of returns about the mean. The volatility of a share price is the standard deviation of the continuously compounded rates of return on the share over a specified period. That is the same as the standard deviation of the differences in the natural logarithms of the stock prices plus dividends, if any, over the period.

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