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Fair Value Assumptions on Stock Option (Detail) - $ / shares
6 Months Ended
Jun. 30, 2015
Jun. 30, 2014
Share based Compensation Arrangement by Share based Payment Award, Fair Value Assumptions, Method Used [Line Items]    
Weighted-average fair value of grant $ 9.07 $ 11.27
Risk-free interest rate 1.28% 1.04%
Expected volatility 45.46% 45.65%
Expected life of options in years 4 years 11 months 1 day 3 years 8 months 16 days
Expected dividend yield 0.00% 0.00%