v3.10.0.1
Employee Benefit Plans (Narrative) (Details)
$ in Thousands
 12 Months Ended
Dec. 31, 2018
USD ($)
pension_plan
Dec. 31, 2017
USD ($)
Dec. 31, 2016
USD ($)
Defined Benefit Plan Disclosure [Line Items]      
Defined contribution plan, expenses $ 11,000 $ 9,900 $ 9,600
Number of Union Pension Plans | pension_plan 2    
Defined Benefit Plan, Health Care Cost Trend Rate Assumed, Next Fiscal Year 5.80%    
Defined Benefit Plan, Ultimate Health Care Cost Trend Rate 4.90%    
Fixed Income Securities [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage 67.00% 67.00%  
Fixed Income Securities [Member] | Scenario, Plan [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage 70.00%    
Equity Securities [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage 30.00% 30.00%  
Equity Securities [Member] | Scenario, Plan [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage 30.00%    
Pension Plan [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Defined Benefit Plan, Benefit Obligation $ 308,949 $ 297,856 225,970
Defined Benefit Plan, Plan Assets, Amount 197,590 198,686 166,906
Defined Benefit Plan, Benefit Obligation, Actuarial Gain (Loss) 21,375 (59,686)  
Defined Benefit Plan, Expected Amortization of Gain (Loss), Next Fiscal Year (5,100)    
Defined Benefit Plan, Expected Amortization of Prior Service Cost (Credit), Next Fiscal Year (200)    
Contributions estimated to be paid 32,100    
Other Postretirement Benefits [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Defined Benefit Plan, Benefit Obligation 12,080 12,760 13,011
Defined Benefit Plan, Plan Assets, Amount 0 0 $ 0
Defined Benefit Plan, Benefit Obligation, Actuarial Gain (Loss) 599 535  
Defined Benefit Plan, Expected Amortization of Gain (Loss), Next Fiscal Year (200)    
Contributions estimated to be paid $ 900    
Salaried Plan and IUOE [Member] | Pension Plan [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Defined Benefit Plan, Benefit Obligation   154,400  
Defined Benefit Plan, Plan Assets, Amount   $ 145,900