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Employee Stock and Benefit Plans (Weighted-Average Assumptions Used to Determine Fair Value of Options Granted) (Detail)
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]      
Expected dividend yield 0.00% 0.00% 0.00%
Risk-free interest rate 2.71% 1.99% 1.59%
Expected term 4 years 3 months 25 days 5 years 3 months 19 days 5 years 1 month 6 days
Volatility 35.00% 36.00% 35.00%