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Stock-Based Compensation (Weighted-Average Assumptions-Options) (Details)
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Volatility, minimum 31.00% 31.00% 37.00%
Volatility, maximum 36.00% 35.00% 45.00%
Risk-free rate of return, minimum 2.54% 1.57% 1.06%
Risk-free rate of return, maximum 3.01% 1.97% 1.41%
Dividend yield 0.25% 0.25% 0.25%
Forfeiture rate 0.00% 0.00%  
Forfeiture rate, minimum     2.65%
Forfeiture rate, maximum     5.26%
Minimum      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Expected term 4 years 1 month 6 days 3 years 9 months 18 days 4 years 4 months 24 days
Maximum      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Expected term 4 years 10 months 24 days 5 years 6 years 1 month 6 days