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Stock-Based Compensation (Stock Options, Black-Scholes Assumptions) (Details)
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]      
Expected dividend yield 1.09% 1.31% 1.25%
Expected stock price volatility 29.89% 32.55% 31.45%
Risk-free interest rate 2.00% 1.35% 1.63%
Expected term of options 5 years 5 years 5 years
Minimum term of publicly traded options used to derive implied volatility of options grants 1 year