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Employee Benefit Plans - Components of Expense (Details) - USD ($)
$ in Thousands
 3 Months Ended 9 Months Ended
Sep. 30, 2017
Sep. 30, 2016
Sep. 30, 2017
Sep. 30, 2016
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]        
Net periodic benefit cost $ 5,909 $ 5,720 $ 17,837 $ 16,978
Defined contribution plans        
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]        
Net periodic benefit cost 2,300 2,073 7,161 6,347
Multi-employer plans        
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]        
Net periodic benefit cost 58 42 191 127
Defined benefit plans        
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]        
Interest cost 6,504 6,839 19,475 20,379
Expected return on plan assets, net of expenses (4,360) (4,616) (13,079) (13,812)
Amortization of actuarial loss 1,150 1,102 3,318 3,097
Total for defined benefit plans 3,294 3,325 9,714 9,664
SERPs        
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]        
Net periodic benefit cost $ 257 $ 280 $ 771 $ 840