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Stock-Based Compensation Plans (Details Textual) (USD $)
In Millions, except Share data, unless otherwise specified
12 Months Ended
Dec. 31, 2011
Y
Dec. 31, 2010
Dec. 31, 2009
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Compensation expense for stock based compensation awards $ 8.1 $ 7.2 $ 4.9
Total Unrecognized compensation cost 4.3    
Stock Based Compensation Plans (Textual) [Abstract]      
Employee compensation charged to operations and capital projects 8.1 7.2 4.9
Compensation cost recognition period 1.6    
Stock options exercisable 196,187    
Weighted average exercise price to exercise stock options exercisable $ 34.51    
Stock options and stock appreciation rights [Member]
     
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period over three years    
Maximum exercisable period of stock options and stock appreciation rights over a period not to exceed ten years    
Total Unrecognized compensation cost 0.8    
Weighted average period 1.4    
Performance shares and units [Member]
     
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period at the end of the three-year    
Total Unrecognized compensation cost 1.9    
Weighted average period 1.7    
Restricted stock and restricted stock unit [Member]
     
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period equal installments annually over three years    
Total Unrecognized compensation cost 1.6    
Weighted average period 1.5    
Annual Incentive Plan and Long Term Incentive Plan [Member]
     
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Compensation expense for stock based compensation awards 11.3 10.6 7.1
Stock Based Compensation Plans (Textual) [Abstract]      
Employee compensation charged to operations and capital projects $ 11.3 $ 10.6 $ 7.1