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Benefit Plans - Savings Plan (Details) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Annual eligible compensation percentage     1.50%
Other accrued retirement compensation $ 30.7 $ 29.0  
First 1%      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Matching contribution to eligible employee contributions 100.00%    
Next 5%      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Percent of eligible compensation 5.00%    
401(K) Plan      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
401(k) plan and ESOP combined expenses $ 15.3 $ 14.4 $ 23.4