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Assumptions Used in Determining Fair Value of Options Granted (Detail)
 12 Months Ended
Dec. 31, 2015
Dec. 31, 2014
Dec. 31, 2013
Fair Value Assumptions Disclosure [Line Items]      
Expected term of options in years 6 years 3 months 18 days 6 years 3 months 18 days 6 years 3 months 18 days
Expected volatility     42.80%
Expected volatility, maximum 40.20% 42.50%  
Expected volatility, minimum 39.00% 41.50%  
Risk-free interest rate     2.50%
Risk-free interest rate, maximum 2.00% 2.30%  
Risk-free interest rate, minimum 1.50% 2.10%  
Expected dividend yield 0.00% 0.00% 0.00%