Employee Benefit Plans - Components of Expense (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Net periodic benefit cost	$ 5,483	$ 5,577	$ 11,928	$ 11,258
Defined contribution plans
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Net periodic benefit cost	1,957	2,086	4,861	4,274
Multi-employer plans
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Net periodic benefit cost	59	42	133	85
Defined benefit plans
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Interest cost	6,486	6,770	12,971	13,540
Expected return on plan assets, net of expenses	(4,360)	(4,599)	(8,720)	(9,196)
Amortization of actuarial loss	1,084	997	2,168	1,995
Total for defined benefit plans	3,210	3,168	6,419	6,339
SERPs
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Net periodic benefit cost	$ 257	$ 281	$ 515	$ 560