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Employee Benefit Plans - Components of Expense (Details) - USD ($)
$ in Thousands
 3 Months Ended 12 Months Ended
Jun. 30, 2016
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]        
Net periodic benefit cost   $ 23,548 $ 22,765 $ 69,063
Pension and Other Postretirement Benefit Expense, Discontinued Operations   (687) (652) (886)
Pension and Other Postretirement Benefit Expense, Continuing Operations   22,861 22,113 68,177
Withdrawal from Multiemployer Defined Benefit Plan [Member]        
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]        
Net periodic benefit cost   0 0 351
Multi-employer plans        
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]        
Net periodic benefit cost   253 168 180
Pension Plan        
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]        
Interest cost   25,966 27,359 30,477
Expected return on plan assets, net of expenses   (17,439) (18,466) (24,320)
Amortization of actuarial loss   4,424 4,406 4,617
Curtailments $ 1,100 0 0 46,793
Total for defined benefit plans   12,951 13,299 57,567
Pension Plan | Defined contribution plans        
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]        
Net periodic benefit cost   9,183 8,265 9,858
SERPs        
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]        
Interest cost   869 910  
Net periodic benefit cost   $ 1,161 $ 1,033 $ 1,107