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Stock Options and Incentive Plans (Narrative) (Details) - USD ($)
$ in Millions
1 Months Ended 12 Months Ended
Mar. 31, 2016
Mar. 31, 2015
Mar. 31, 2014
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Long Term Incentive Plan [Member]            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Shares of stock authorized for payment of awards       235,299    
Shares issued for long term incentive plan 26,146 35,393 29,321      
Cash payments in connection with long term incentive plan $ 0.8 $ 1.2 $ 1.1      
Deferred compensation expense       $ 2.7 $ 3.0 $ 2.4
Vesting period       3 years    
Additional share based compensation expense expected to be recognized in next twelve months       $ 0.7    
Additional share based compensation expense expected to be recognized in two years       0.6    
Long Term Incentive Plan [Member] | Management [Member]            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Shares issued for long term incentive plan 26,774 19,571 15,910      
Cash payments in connection with long term incentive plan $ 1.9 $ 1.5 $ 1.4      
Deferred compensation expense       $ 3.3 3.4 2.7
Stock Options [Member]            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Contractual term of stock options, in years       20 years    
Length of time options are valid after retirement, in years       10 years    
Aggregate intrinsic value of vested options       $ 1.7    
Aggregate intrinsic value of options exercised       0.5 0.2 0.7
Phantom Stock Plan [Member]            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Deferred compensation expense       3.8 2.6 2.2
Compensation cost not yet recognized       $ 8.3    
Vesting period       5 years    
Compensation cost recognition period       2 years    
Additional Restricted Stock Plan [Member] | Management [Member]            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Deferred compensation expense         0.3 0.7
Restricted Stock [Member]            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Deferred compensation expense       $ 0.7 0.6 1.4
Vesting period       5 years    
Maximum [Member] | Long Term Incentive Plan [Member] | Management [Member]            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Earned incentive compensation paid in shares of Class A Common Stock       50.00%    
Minimum [Member] | Long Term Incentive Plan [Member] | Management [Member]            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Earned incentive compensation paid in shares of Class A Common Stock       40.00%    
Pension Plans [Member]            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Deferred compensation plan expense       $ 5.5 4.8 4.3
Pension Plans [Member] | Maximum [Member]            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Percent of employee contribution matched by the Company       100.00%    
Pension Plans [Member] | Minimum [Member]            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Percent of employee contribution matched by the Company       50.00%    
Profit Sharing Plan [Member]            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Deferred compensation plan expense       $ 2.9 $ 2.4 $ 1.5