Income Taxes (Tables)

12 Months Ended

Dec. 31, 2012

Income Tax Disclosure [Abstract]

Summary of Provision for Income Taxes from Continuing Operations

The following table summarizes our provision for income taxes from continuing operations for the periods presented: 

	Year Ended December 31,
	2012			2011			2010
Current income taxes (benefit)
Federal	$	—		$	1,279		$	(109,240	)
State	(26		)	(3,933		)	876
	(26		)	(2,654		)	(108,364		)
Deferred income taxes (benefit)
Federal	(60,676		)	(80,529		)	67,999
State	(8,000		)	(4,972		)	(2,486		)
	(68,676		)	(85,501		)	65,513
	$	(68,702	)	$	(88,155	)	$	(42,851	)

Intra Period Allocation of Income Taxes

The following table summarizes the intra-period allocation of income taxes for the periods presented: 

	Year Ended December 31,
	2012			2011			2010
Continuing operations	$	(68,702	)	$	(88,155	)	$	(42,851	)
Discontinued operations	—			—			3,384
Gain on sale of discontinued operations	—			—			35,116
	$	(68,702	)	$	(88,155	)	$	(4,351	)

Income Taxes Reconciliation

The following table reconciles the difference between the income taxes computed by applying the statutory tax rate to income from continuing operations before income taxes and our reported income tax expense for the periods presented: 

	Year Ended December 31,
	2012					2011					2010
Computed at federal statutory rate	$	(60,652	)	(35.0	)%	$	(77,374	)	(35.0	)%	$	(37,862	)	(35.0	)%
State income taxes, net of federal income tax benefit	(8,026		)	(4.6	)%	(4,825		)	(2.2	)%	(1,927		)	(1.8	)%
Other, net	(24		)	—	%	(5,956		)	(2.7	)%	(3,062		)	(2.8	)%
	$	(68,702	)	(39.6	)%	$	(88,155	)	(39.9	)%	$	(42,851	)	(39.6	)%

Summary of Principal Components of Net Deferred Income Tax Liability

The following table summarizes the principal components of our net deferred income tax liability as of the dates presented: 

	As of December 31,
	2012			2011
Deferred tax liabilities:
Property and equipment	$	311,002		$	429,568
Fair value of derivative instruments	5,268			3,006
Convertible notes	—			60
Total deferred tax liabilities	316,270			432,634
Deferred tax assets:
Pension and postretirement benefits	2,864			3,046
Share-based compensation	10,760			8,838
Net operating loss ("NOL") carryforwards	102,407			150,953
Other	15,788			10,642
	131,819			173,479
Less:  Valuation allowance	(26,686		)	(19,492		)
Total deferred tax assets	105,133			153,987
Net deferred tax liability	$	211,137		$	278,647