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Common Stock - Assumption Used in Determination of Fair Value of Share Based Payment Awards (Detail) (USD $)
In Millions, unless otherwise specified
12 Months Ended
Dec. 31, 2013
Dec. 31, 2012
Dec. 31, 2011
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]      
Expected volatility 50.10% 51.70% 53.20%
Risk-free interest rate 0.90% 0.90% 2.10%
Expected dividends $ 0.75 $ 0.57 $ 0.44
Expected term (in years) 3 years 4 months 24 days 3 years 2 months 12 days 3 years 1 month 6 days