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Stock-Based Compensation Plans Compensation Costs from Equity Awards (Details) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2015
Dec. 31, 2014
Dec. 31, 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Compensation costs from the Company's stock-based awards $ 14.3 $ 12.7 $ 11.7
Compensation costs related to non-vested awards not yet recognized $ 19.3    
Period over which non-vested awards will be recognized 3 years    
Weighted average period over which non-vested awards will be recognized 1 year 3 months 10 days    
Income tax benefit recognized $ 4.2 4.4 5.3
Total income tax benefit realized from exercise of equity awards $ 3.9 $ 11.0 17.7
Acceleration of Equity Awards for RailAmerica Employee Terminations [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Compensation costs from the acceleration of equity awards     $ 5.1