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Stock-Based Compensation (Fair Value Assumptions) (Details) - Performance-based Shares [Member]
12 Months Ended
Dec. 31, 2015
Dec. 31, 2014
Dec. 31, 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Risk-free interest rate 1.10% 0.80% 0.30%
Expected term (years) 3 years 3 years 3 years
Expected stock price volatility 17.40% 21.50% 22.40%