Income Taxes (Details) (USD $)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Current
Federal	$ 56,544,000	$ 24,618,000	$ 39,749,000
State	10,841,000	563,000	(1,714,000)
Total	67,385,000	25,181,000	38,035,000
Deferred
Federal	111,147,000	57,704,000	46,599,000
State	27,233,000	23,225,000	28,145,000
Total	138,380,000	80,929,000	74,744,000
Total income tax expense	205,765,000	106,110,000	112,779,000
Reconciliation of actual provision for income taxes and provision for income taxes resulting from the use of federal statutory income tax
Statutory federal income tax rate (as a percent)	35.00%	35.00%	35.00%
Computed "expected" federal income tax	169,938,000	83,244,000	82,316,000
State income tax, net of federal income tax benefit	17,513,000	9,609,000	8,989,000
Deferred tax adjustment related to change in overall state tax rate	15,220,000	13,596,000	19,068,000
Other, net	3,094,000	(339,000)	2,406,000
Total income tax expense	205,765,000	106,110,000	112,779,000
Deferred Tax Assets
Net operating loss carryforward	78,182,000	137,422,000
Alternative minimum tax carryforward	182,212,000	125,862,000
Foreign tax credits	4,822,000	4,923,000
Derivatives and hedging	3,946,000
Incentive compensation	36,450,000	30,985,000
Deferred compensation	11,988,000	8,485,000
Post-retirement benefits	13,965,000	16,498,000
Other	3,619,000	7,078,000
Total	335,184,000	331,253,000
Deferred Tax Liabilities
Properties and equipment	1,321,241,000	1,199,213,000
Derivatives and hedging		19,915,000
Total	1,321,241,000	1,219,128,000
Net deferred tax liabilities	986,057,000	887,875,000
State tax effected net operating losses
Tax benefits related to employee stock-based compensation included in net operating loss carryforwards	66,400,000
Reconciliation of unrecognized tax benefits
Additions based on tax provisions related to the current year	3,700,000
Unrecognized tax benefit balance at the end of the period	3,700,000
Recognized tax benefits that would not affect the effective tax rate	2,400,000
State Tax Reporting
State tax effected net operating losses
Net operating loss carryforwards	378,600,000
Federal
State tax effected net operating losses
Net operating loss carryforwards	$ 221,100,000