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Share-Based Compensation Plans - Performance Share Units (Details) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Dec. 31, 2013
Payout Levels (in units):        
Share-based compensation $ 27.1 $ 31.1 $ 40.6  
Performance share units        
Payout Levels (in units):        
Threshold Award (in shares) 65,141 82,298 94,608 76,120
Target Award (in shares) 130,282 164,595 189,215 152,240
Outstanding Award (in shares) 260,564 329,190 378,430 304,480
Share-based compensation $ 9.1 $ 17.1 $ 20.1  
Performance share units | February 11, 2014 and May 1, 2014        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Vesting percentage     100.00%  
Units Forfeited (at Target Award level) 10,928      
Performance share units | February 11, 2015        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Vesting percentage   100.00%    
Units Forfeited (at Target Award level) 7,796      
Performance share units | February 16, 2016        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Vesting percentage 100.00%      
Performance share units | February 14, 2013        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Shares Issued (in shares) 56,059      
Performance share units | December 31, 2014 | February 14, 2013        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Vesting percentage       50.00%
Performance share units | December 31, 2015 | February 14, 2013        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Vesting percentage       50.00%
Minimum        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Performance period range 1 year      
Maximum        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Performance period range 3 years