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Share-Based Compensation - Summary of Restricted Stock and Performance Units Activity (Parenthetical) (Details) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Restricted Stock      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Fair value of awards vested $ 18.9 $ 23.3 $ 28.8
Performance Units      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Fair value of awards vested $ 5.4 $ 7.5 $ 1.1
Stock Issued During Period, Shares, Restricted Stock Award, Gross 46,876 67,391 21,111
Common Stock Dividends, Shares 3,507 8,791 507