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Stock-Based Compensation (Details)
$ in Millions
12 Months Ended
Dec. 31, 2016
USD ($)
shares
Dec. 31, 2015
USD ($)
shares
Dec. 31, 2014
USD ($)
shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Compensation expense $ 5.3 $ 4.4 $ 3.1
Compensation expense tax (expense) benefit (1.8) (1.8) 0.1
Compensation expense not yet recognized for nonvested awards $ 5.1    
Nonvested awards, total compensation cost not yet recognized, period for recognition 2 years    
Shares vested in period, total fair value $ 3.5 $ 2.8 $ 2.1
Share-based Compensation, Significant Assumptions      
Risk-free interest rate 0.85% 1.06%  
Expected life, in years 3 years 3 years  
Expected volatility, minimum 17.10% 14.20%  
Expected volatility, maximum 22.10% 19.00%  
Dividend yield 3.40% 3.50%  
Performance Shares [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Performance and vesting period 3 years    
Performance Shares [Member] | Minimum [Member]      
Share-based Compensation, Significant Assumptions      
Percent of shares issued based on company performance 0.00%    
Performance Shares [Member] | Maximum [Member]      
Share-based Compensation, Significant Assumptions      
Percent of shares issued based on company performance 200.00%    
Stock Compensation Plan [Member] | Minimum [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Performance and vesting period 1 year    
Stock Compensation Plan [Member] | Maximum [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Performance and vesting period 5 years    
Executive retirement/retention program [Member] | Restricted Stock [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Performance and vesting period 5 years    
Deferred Stock Unit [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Maximum percentage of compensation to be deferred 100.00%    
Maximum number of years for distribution payments 10    
Deferred stock units issued during period, shares | shares 28,338 35,030 26,460
Deferred stock units total compensation expense $ 2.4 $ 1.3 $ 2.3
Common Stock [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Number of shares authorized | shares     600,000
Number of shares available for grant | shares 870,186