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Employee Benefit Plans - Components of Expense (Details) - USD ($)
$ in Thousands
 3 Months Ended
Mar. 31, 2018
Mar. 31, 2017
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]    
Net periodic benefit cost $ 4,228 $ 6,445
Pension and Other Postretirement Benefit Expense, Discontinued Operations 203 191
Pension and Other Postretirement Benefit Expense, Continuing Operations 4,025 6,254
Defined contribution plans    
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]    
Net periodic benefit cost 2,793 2,904
Multi-employer plans    
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]    
Net periodic benefit cost 47 74
Defined benefit plans    
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]    
Interest cost 5,925 6,486
Expected return on plan assets, net of expenses (5,732) (4,360)
Amortization of actuarial loss 921 1,084
Total for defined benefit plans 1,114 3,210
SERPs    
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]    
Net periodic benefit cost $ 274 $ 257