Income Taxes (Details 2) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Components of deferred income tax assets and deferred tax liabilities
Deferred tax assets	$ 561,216,000	$ 620,506,000
Less: Valuation allowance	169,870,000	426,585,000	420,100,000
Net deferred tax assets	391,346,000	193,921,000
Deferred tax liabilities	411,443,000	414,655,000
Net deferred tax liability	20,097,000	220,734,000
Deferred tax assets:
Federal net operating loss carryforwards	288,675,000	365,336,000
State net operating loss carryforwards	180,777,000	173,501,000
Alternative minimum tax credits	6,591,000	6,591,000
Accrued insurance, pension liability and other	85,173,000	75,078,000
Total deferred tax asset	561,216,000	620,506,000
Deferred tax liabilities:
Property and equipment	287,992,000	294,006,000
Intangible assets and other	123,451,000	120,649,000
Total deferred tax liabilities	411,443,000	414,655,000
Estimated income tax deductions related to share-based payments	90,000,000
Estimated excess income tax benefits pertaining to share-based payments recognized as an increase in additional paid in capital at current income tax rates	31,000,000
Details of net operating loss carryforwards
Alternative minimum tax credits		6,600,000
U.S. federal
Details of net operating loss carryforwards
Net operating loss carryforwards	900,000,000	1,100,000,000
State
Details of net operating loss carryforwards
Net operating loss carryforwards	$ 4,700,000,000	$ 4,700,000,000