Annual report pursuant to Section 13 and 15(d)

Share Based Compensation (Narrative) (Details)

v3.8.0.1
Share Based Compensation (Narrative) (Details) - 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 [Line Items]      
Common stock authorized for grant under the Share Incentive Plans 6,650,000    
Exercise price per share of options granted, percentage, minimum 100.00%    
Additional compensation expense $ 32.5 $ 14.1 $ 14.9
Share-based Compensation Arrangement by Share-based Payment Award Accelerated Compensation Cost 16.6    
Unrecognized compensation costs 4.7    
Compensation costs expected to be recognized in 2018 2.2    
Compensation costs expected to be recognized in 2019 $ 1.3    
Weighted average values of grants $ 37.20 $ 31.31 $ 41.09
Weighted average expected volatility 25.50% 26.50% 25.16%
Weighted average discount rates 1.92% 1.59% 1.79%
Expected lives 5 years 215 days 6 years 91 days 6 years 11 days
Total grant date fair value of restricted stock and restricted stock units vested $ 26.1 $ 10.8 $ 10.8
Aggregate intrinsic value of exercised stock options $ 5.6 $ 1.4 $ 1.0
Weighted average remaining contractual term for total outstanding stock options 5 years 131 days    
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Weighted Average Remaining Contractual Term 4 years 18 days    
Aggregate intrinsic value of options outstanding $ 11.8    
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Intrinsic Value $ 8.4    
Restricted Stock | Minimum [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Restricted stock and restricted stock units vesting period 1 year    
Restricted Stock | Maximum [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Restricted stock and restricted stock units vesting period 5 years    
Employee Stock Option [Member] | Minimum [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Restricted stock and restricted stock units vesting period 1 year    
Employee Stock Option [Member] | Maximum [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Restricted stock and restricted stock units vesting period 5 years    
Employee Stock [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Common stock authorized for grant under the Share Incentive Plans 600,000    
Share-based Compensation Arrangement by Share-based Payment Award, Discount from Market Price, Purchase Date 85.00%    
Common stock made available for purchase under the Employee Stock Purchase Plans, offering period, months 6