Employee Benefit Plans - Components of Expense (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Net periodic benefit cost	$ 3,317	$ 3,411	$ 7,925	$ 7,639
Pension and Other Postretirement Benefit Expense, Discontinued Operations	0	174	0	377
Pension and Other Postretirement Benefit Expense, Continuing Operations	3,317	3,237	7,925	7,262
Defined contribution plans
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Net periodic benefit cost	1,695	1,978	4,690	4,771
Multi-employer plans
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Net periodic benefit cost	58	44	99	91
Defined benefit plans
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Interest cost	5,800	5,925	11,600	11,850
Expected return on plan assets, net of expenses	(5,058)	(5,733)	(10,116)	(11,465)
Amortization of actuarial loss and prior service cost	572	920	1,144	1,841
Total for defined benefit pension plans	1,314	1,112	2,628	2,226
SERPs
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Net periodic benefit cost	$ 250	$ 277	$ 508	$ 551