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Stock-based Compensation Plans - Narrative (Details) - USD ($)
$ / shares in Units, $ in Millions
3 Months Ended 9 Months Ended
Sep. 30, 2017
Sep. 30, 2016
Sep. 30, 2017
Sep. 30, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Stock-based compensation cost $ 1.2 $ 1.9 $ 3.5 $ 5.5
Total unrecognized compensation cost related to non-vested share-based compensation arrangements $ 10.6   $ 10.6  
Compensation cost not yet recognized, period for recognition     1 year 8 months 2 days  
Restricted Stock Units        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Granted, number of shares (in shares)     167,086 124,077
Grants in period, weighted average grant date fair value (in dollars per share)     $ 38.78 $ 38.21
Performance-Based Restricted Stock Units        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Granted, number of shares (in shares)     126,220 156,576
Grants in period, weighted average grant date fair value (in dollars per share)     $ 39.34 $ 38.47
Shares earned (in shares)       0