Employee Benefit Plans - Components of Expense (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Net periodic benefit cost	$ 4,608	$ 4,228
Pension and Other Postretirement Benefit Expense, Discontinued Operations	0	203
Pension and Other Postretirement Benefit Expense, Continuing Operations	4,608	4,025
Defined contribution plans
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Net periodic benefit cost	2,995	2,793
Multi-employer plans
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Net periodic benefit cost	41	47
Defined benefit plans
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Interest cost	5,800	5,925
Expected return on plan assets, net of expenses	(5,058)	(5,732)
Amortization of actuarial loss and prior service cost	572	921
Total for defined benefit pension plans	1,314	1,114
SERPs
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Net periodic benefit cost	$ 258	$ 274