Income Taxes (Tables)

12 Months Ended

Dec. 31, 2012

Income Tax Disclosure [Abstract]

Schedule of componenets of provision for income taxes

The provision for income taxes consists of the following:

	For the Years Ended December 31,
	2012			2011			2010
	(in thousands)
Current portion of income tax benefit (expense)
Federal	$	—		$	1,757		$	(2,903	)
State	(370		)	(1,553		)	(639		)
Deferred portion of income tax benefit (expense)	29,638			(123,789		)	(114,517		)
Total income tax benefit (expense)	$	29,268		$	(123,585	)	$	(118,059	)
Effective tax rate	35.0		%	36.5		%	37.5		%

Schedule of Deferred Tax Assets and Liabilities [Table Text Block]

The components of the net deferred income tax liabilities are as follows:

	As of December 31,
	2012			2011
	(in thousands)
Deferred tax liabilities:
Oil and gas properties	$	678,624		$	639,485
Unrealized derivative asset	15,942			13,274
Other	6,443			4,129
Total deferred tax liabilities	701,009			656,888
Deferred tax assets:
Federal and state tax net operating loss carryovers	113,522			23,651
Net Profits Plan liability	29,233			40,148
Stock compensation	18,026			17,728
Pension liability	6,849			5,902
Federal and state tax credit carryovers	5,271			4,301
Other long-term liabilities	4,619			4,908
Total deferred tax assets	177,520			96,638
Valuation allowance	(5,315		)	(3,791		)
Net deferred tax assets	172,205			92,847
Total net deferred tax liabilities	528,804			564,041
Less: current deferred income tax liabilities	(5,442		)	(3,307		)
Add: current deferred income tax assets	14,021			7,529
Non-current net deferred tax liabilities	$	537,383		$	568,263
Current federal income tax refundable	$	2,511		$	5,581
Current state income tax refundable	$	853		$	—
Current state income tax payable	$	—		$	774

Schedule of Effective Income Tax Rate Reconciliation [Table Text Block]

Federal income tax expense differs from the amount that would be provided by applying the statutory United States federal income tax rate to income before income taxes primarily due to the effect of state income taxes, R&D credits, percentage depletion, changes in valuation allowances, and other permanent differences, as follows:

	For the Years Ended December 31,
	2012			2011			2010
	(in thousands)
Federal statutory tax benefit (expense)	$	29,231		$	(118,652	)	$	(110,214	)
(Increase) decrease in tax resulting from:
State tax benefit (expense) (net of federal benefit)	992			(6,458		)	(7,750		)
Research and development credit	970			4,516			—
Change in valuation allowance	(1,524		)	(1,627		)	1,039
Statutory depletion	210			341			266
Other	(611		)	(1,705		)	(1,400		)
Income tax benefit (expense)	$	29,268		$	(123,585	)	$	(118,059	)

Summary of Positions for which Significant Change in Unrecognized Tax Benefits is Reasonably Possible [Table Text Block]

The total amount recorded for unrecognized tax benefits is presented below:

	For the Years Ended December 31,
	2012		2011			2010
	(in thousands)
Beginning balance	$	1,961	$	807		$	884
Additions based on tax positions related to current year	—		1,172			—
Additions for tax positions of prior years	317		183			244
Reductions for lapse of statute of limitations	—		(201		)	(321		)
Ending balance	$	2,278	$	1,961		$	807