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Stock-Based Compensation - Weighted Average Grant Date Fair Value of Option Shares Granted and Assumptions Used to Estimate Those Values Using Black-Scholes Option Pricing Model (Detail) (USD $)
3 Months Ended
Mar. 31, 2013
Mar. 31, 2012
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]    
Weighted average grant date fair value $ 8.33 $ 4.44
Risk-free interest rate 1.20% 1.10%
Dividend yield 1.47% 2.57%
Volatility factor 49.00% 51.00%
Expected option life 6 years 6 years