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Fair Value of Granted Options and Stock Appreciation Rights Estimated Using Black- Scholes Pricing Model (Detail) (Stock Option and Stock Appreciation Rights, USD $)
12 Months Ended
Dec. 31, 2011
Stock Option and Stock Appreciation Rights
 
Schedule of Weighted Average Fair Values of Stock Options [Line Items]  
Weighted average expected dividend yield 5.80%
Weighted average expected implied volatility 30.00%
Weighted average risk-free interest rate 1.50%
Expected holding period (in years) 5 years
Weighted average fair value of awards $ 4.90