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Share-Based Payments - Textual (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]      
Weighted-average fair value per share (in dollars per share) $ 11.55 $ 11.55 $ 15.11
Unrecognized compensation cost $ 1.3    
Intrinsic value of stock options exercised $ 29.0 $ 9.1 $ 4.2
2008 Amended and Restated Equity Incentive Plan [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Shares authorized for grant under the Plan (shares) 9,000,000 9,000,000
2016 Omnibus Performance Incentive Plan [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Shares authorized for grant under the Plan (shares) 14,000,000    
Stock Options [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Expiration period 10 years    
Vesting period 3 years    
Share-based compensation expense $ 0.8 $ 1.6 $ 1.6
Weighted-average recognition period for unrecognized compensation cost 23 months    
Employment Based SARS [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Shares granted during the period (shares) 122,976    
Stock Appreciation Rights (SARs) [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Share-based compensation expense $ 26.0 $ 5.8 3.5
Weighted-average recognition period for unrecognized compensation cost 27 months    
Unrecognized compensation cost related to unvested SARs $ 15.0    
Weighted-average fair value per share of awards granted (in dollars per share) $ 199.41 $ 84.33  
Outstanding awards (shares) 252,100    
Performance and Employment Based SARS [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Shares granted during the period (shares) 129,124    
Restricted Stock [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Share-based compensation expense $ 19.6 $ 18.7 $ 19.5
Weighted-average recognition period for unrecognized compensation cost 21 months    
Unrecognized compensation cost related to unvested SARs $ 24.0    
Weighted-average fair value per share of awards granted (in dollars per share) $ 42.85 $ 33.56 $ 27.86
Fair value of vested shares $ 17.7 $ 24.3 $ 41.0
Awards issued during period (shares) 504,000    
Non-employee Directors [Member] | Restricted Stock Units (RSUs) [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Weighted-average fair value per share of awards granted (in dollars per share) $ 47.30 $ 40.75 $ 42.46
Outstanding awards (shares) 471,696    
Awards issued during period (shares) 27,594 32,031 30,744
Compensation expense recognized $ 1.3 $ 1.3 $ 1.3
Unrecognized compensation cost $ 0.0    
Non-employee Directors [Member] | Dividend Equivalent, RSU [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Awards issued during period (shares) 9,968 10,248 7,645