Annual report pursuant to Section 13 and 15(d)

Stock Plans and Management Compensation (Details 3)

v3.8.0.1
Stock Plans and Management Compensation (Details 3) - USD ($)
$ / shares in Units, $ in Millions
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Share-Based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]      
Excess Tax Benefit from Share-Based Compensation, Financing Activities $ 8.0 $ 13.4 $ 7.0
Percentage of Premium Paid Out in Deferred Company Common Stock 20.00%    
Performance Shares [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Expected Life of Award 2 years 10 months 24 days 2 years 10 months 24 days 2 years 10 months 24 days
Share-Based Compensation Expense $ 6.7 $ 6.0 $ 7.9
Share-Based Compensation Expense, Tax Benefit 2.6 2.3 3.0
Fair Value of Shares Vested During the Period $ 5.5 $ 9.1 $ 7.5
Share-Based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]      
Outstanding at January 1 91,000    
Awarded Grants in Period 114,000    
Forfeited (4,000)    
Vested (99,000)    
Outstanding at December 31 102,000 91,000  
Weighted Average Grant Date Fair Value $ 50.69 $ 43.91  
Awarded - Weighted Average Grant Date Fair Value 63.43    
Forfeited - Weighted Average Grant Date Fair Value 47.10    
Vested - Weighted Average Grant Date Fair Value $ 59.34    
Unrecognized Compensation Cost $ 2.3    
Unrecognized Compensation Cost, Period for Recognition 1 year 6 months    
Share-based Compensation Award, Tranche Two [Member] | Performance Shares [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Weighted Average Price at Grant Date (in dollars per share) $ 58.77 $ 37.76 $ 52.39
Share-Based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]      
Awarded Grants in Period 26,300 37,430 22,990
Share-based Compensation Award, Tranche One [Member] | Performance Shares [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Weighted Average Price at Grant Date (in dollars per share) $ 64.82 $ 38.54 $ 56.17
Risk-Free Interest Rate 1.50% 0.80% 1.00%
Dividend Yield 1.10% 1.00% 0.90%
Volatility Factor 38.30% 40.80% 39.20%