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Assumptions Used for Calculating Fair Values of Stock Option Awards (Detail) (USD $)
3 Months Ended
Mar. 31, 2014
Mar. 31, 2013
Stock Options Granted    
Weighted average grant date fair value, per share $ 26.46 $ 19.84
Weighted average assumptions used:    
Expected volatility 52.80% 66.40%
Expected lives 5 years 0 months 0 days 4 years 10 months 24 days
Risk-free interest rates 1.70% 0.70%
Dividend yields 0.00% 0.00%