Employee Benefit Plans - Components of Expense (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Net periodic benefit cost	$ 4,818	$ 5,716	$ 12,743	$ 13,355
Pension and Other Postretirement Benefit Expense, Discontinued Operations	0	132	0	509
Pension and Other Postretirement Benefit Expense, Continuing Operations	4,818	5,584	12,743	12,846
Defined contribution plans
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Net periodic benefit cost	2,743	2,137	7,433	6,908
Multi-employer plans
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Net periodic benefit cost	4	50	103	141
Defined benefit plans
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Interest cost	5,865	5,962	17,465	17,812
Expected return on plan assets, net of expenses	(4,865)	(5,734)	(14,981)	(17,199)
Amortization of actuarial loss and prior service cost	823	1,026	1,967	2,867
Total for defined benefit pension plans	1,823	1,254	4,451	3,480
SERPs
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Net periodic benefit cost	$ 248	$ 2,275	$ 756	$ 2,826