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Employee Benefit Plans Defined Contribution Plans (Narrative) (Details) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Annual Retirement Contribution (ARC) [Member]      
Defined contribution plans, ARC, maximum employee contribution percentage 5.00%    
Defined contribution plan, employer matching contribution, percent 3.00%    
Defined contribution plans, ARC, contributions made during period $ 6.0 $ 5.8 $ 5.3
Defined contribution plans, ARC, hourly associates, contributions made during period $ 1.1 1.9 2.5
Salaried Savings Plan [Member]      
Defined contribution plans, maximum company match, salaried voluntary savings plan 50.00%    
Defined contribution plans, ARC, maximum employee contribution percentage 10.00%    
Defined contribution plans, salaried voluntary savings plan, matching contributions during the period $ 9.3 5.2 4.6
Hourly Voluntary Savings Plan [Member]      
Defined contribution plans, ARC, maximum employee contribution percentage 6.00%    
Defined Contribution Plans, Maximum Company Match, Hourly Voluntary Savings Plan 25.00%    
Defined contribution plans, hourly voluntary savings plan, matching contributions during the period $ 0.7 $ 0.4 $ 0.1