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Share-Based Compensation Plan (Restricted Stock Unit Activity) (Details) - Restricted Stock Units (RSUs) [Member] - $ / shares
12 Months Ended
Dec. 31, 2015
Dec. 31, 2014
Dec. 31, 2013
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Number of Shares [Roll Forward]      
Beginning balance, Number of Units 204,319 188,532 156,510
Granted, Number of Units 85,645 73,468 71,768
Converted into shares of common stock, Number of Units (70,166) (52,008) (36,416)
Forfeited/expired, Number of Units (11,809) (5,673) (3,330)
Ending balance, Number of Units 207,989 204,319 188,532
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Weighted Average Grant Date Fair Value [Abstract]      
Beginning balance, Weighted Average Grant Date Fair Value Per Share (USD per share) $ 24.14 $ 21.49 $ 20.83
Granted, Weighted Average Grant Date Fair Value Per Unit (USD per Unit) 28.52 27.49 23.42
Converted into shares of common stock, Weighted Average Grant Date Fair Value Per Unit (USD per Unit) 22.51 19.23 22.44
Forfeited/expired, Weighted Average Grant Date Fair Value Per Unit (USD per Unit) 25.61 24.31 21.67
Ending balance, Weighted Average Grant Date Fair Value Per Share (USD per share) $ 26.41 $ 24.14 $ 21.49