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STOCK BASED COMPENSATION - Assumptions used in Black-Scholes Model (Detail) (USD $)	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Weighted average fair value at grant date	$ 21.57	$ 19.90
Expected term (in years)	6 years	6 years
Expected volatility	27.10%	27.87%
Expected dividend yield	0.00%	0.00%
Risk free interest rate	0.99%	1.08%

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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