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Stock-Based Compensation - Assumptions for Fair Value of Options Granted (Details)
3 Months Ended
Mar. 31, 2018
Mar. 31, 2017
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]    
Risk-free interest rate 2.10% 2.00%
Weighted average expected life 5 years 9 months 18 days 5 years 9 months 18 days
Expected volatility 21.40% 25.10%
Dividend yield 1.50% 1.90%