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Share-Based Compensation - Assumptions for Estimation of Fair Values of Stock Appreciation Rights Granted During Reporting Periods (Detail) (USD $)	6 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Risk-free interest rate	1.33%	1.67%
Expected volatility	21.00%	22.00%
Expected dividend yield	2.60%	2.50%
Expected life	8 years	7 years 10 months 24 days
Fair value derived	$ 12.08	$ 12.61

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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