Employee Benefit Plans - Components of Expense (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Jun. 30, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]
Net periodic benefit cost		$ 22,765	$ 69,063	$ 22,132
Pension and Other Postretirement Benefit Expense, Discontinued Operations		0	(482)	(8,985)
Pension and Other Postretirement Benefit Expense, Continuing Operations		22,765	68,581	13,147
Defined benefit plans
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]
Service cost		0	0	85
Interest cost		27,359	30,477	25,539
Expected return on plan assets, net of expenses		(18,466)	(24,320)	(23,481)
Amortization of actuarial loss		4,406	4,617	2,861
Curtailments	$ 1,100	0	46,793	0
Total for defined benefit plans		13,299	57,567	5,004
Multi-employer plans
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]
Net periodic benefit cost		168	180	393
Withdrawal from GCIU multi-employer plan
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]
Net periodic benefit cost		0	351	4,100
SERPs
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]
Service cost		0	0
Interest cost		910	747
Net periodic benefit cost		1,033	1,107	896
Defined contribution plans
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]
Net periodic benefit cost		$ 8,265	$ 9,858	$ 11,739