Income Taxes (Details 3) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Deferred income tax assets:
Self-insurance accruals	$ 93,352	$ 81,908
Net operating loss carryforwards	429,458	377,740
Alternative minimum taxes	10,727	10,727
Accrued compensation and benefits	76,363	68,626
Federal benefit on state tax positions	18,912	18,847
Pension benefits	148,671	157,082
Miscellaneous other accruals	32,763	33,090
Deferred tax assets gross	810,246	748,020
Valuation allowance	(14,991)	(24,742)
Deferred tax assets net	795,255	723,278
Deferred income tax liabilities:
Property and equipment bases difference	(2,362,194)	(2,149,574)
Other	(20,583)	(16,996)
Deferred Tax Liabilities, Gross	(2,382,777)	(2,166,570)
Net deferred income tax liability	$ (1,587,522)	$ (1,443,292)