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Retirement Plans - Narrative (Details) - USD ($)
$ in Millions
3 Months Ended 9 Months Ended
Sep. 30, 2018
Sep. 30, 2018
Oct. 15, 2018
Sep. 15, 2018
Dec. 31, 2017
Defined Benefit Plan Disclosure [Line Items]          
Pension plan contribution $ 0.4 $ 0.8      
Required contributions by employer 1.7 1.7   $ 1.7 $ 0.0
Anticipated contributions in the next twelve months $ 4.0 $ 4.0      
Subsequent Event          
Defined Benefit Plan Disclosure [Line Items]          
Required contributions by employer     $ 0.4