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Share-Based Compensation Weighted Average Assumptions and Fair Values Used for ESPP (Detail) - Employee Stock Purchase Plan - USD ($)
12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Share based Compensation Arrangement by Share based Payment Award, Fair Value Assumptions, Method Used [Line Items]      
Expected term in years 6 months 6 months 6 months
Weighted average expected volatility of the Company's underlying common stock 41.80% 25.90% 23.70%
Risk-free interest rate 0.45% 0.12% 0.08%
Expected dividend yield $ 0 $ 0 $ 0
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Weighted Average Grant Date Fair Value $ 29.16 $ 29.27 $ 24.00