Income Taxes

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	)

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	)

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	)%

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

As of December 31, 2012, we had federal NOL carryforwards of approximately $203.8 million, which expire starting in 2031, and state NOL carryforwards of approximately $47.8 million, which expire between 2024 and 2032. As of December 31, 2012 and 2011, valuation allowances of $41.0 million and $30.0 million, respectively, had been recorded for deferred tax assets associated with state NOL carryforwards that were not more-likely-than-not to be realized.

As of December 31, 2011, we classified $31.2 million of deferred tax assets as a current income tax receivable attributable to the federal NOL expected to be utilized. In 2012, we received a federal tax refund of approximately $32 million from the carryback of the 2011 federal NOL, and the remainder of the NOL is available for carryforward.

We have no liability for unrecognized tax benefits as of December 31, 2012 and 2011. There were no interest and penalty charges recognized during the years ended December 31, 2012 , 2011 and 2010. Tax years from 2009 forward remain open for examination by the Internal Revenue Service and various state jurisdictions.