Income Taxes (Tables)

12 Months Ended

Dec. 31, 2011

Income Tax Disclosure [Abstract]

Schedule of componenets of provision for income taxes

	For the Years Ended December 31,
	2011			2010			2009
	(in thousands)
Current portion of income tax (expense) benefit
Federal	$	1,757		$	(2,903	)	$	21,926
State	(1,553		)	(639		)	(1,567		)
Deferred portion of income tax (expense) benefit	(123,789		)	(114,517		)	39,735
Total income tax (expense) benefit	$	(123,585	)	$	(118,059	)	$	60,094
Effective tax rate	36.5		%	37.5		%	37.7		%

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

	As of December 31,
	2011			2010
	(in thousands)
Deferred tax liabilities:
Oil and gas properties	$	639,485		$	528,652
Unrealized derivative asset	13,274			—
Interest on 3.50% Senior Convertible Notes	2,256			2,219
Other	1,873			2,723
Total deferred tax liabilities	656,888			533,594
Deferred tax assets:
Net Profits Plan liability	40,148			50,922
Stock compensation	17,728			13,143
Federal and state tax net operating loss carryovers	23,651			10,772
Federal and state tax credit carryovers	4,301			—
Unrealized derivative liability	—			6,929
Other long-term liabilities	10,810			19,740
Total deferred tax assets	96,638			101,506
Valuation allowance	(3,791		)	(2,164		)
Net deferred tax assets	92,847			99,342
Total net deferred tax liabilities	564,041			434,252
Less: current deferred income tax liabilities	(3,307		)	(2,710		)
Add: current deferred income tax assets	7,529			11,593
Non-current net deferred tax liabilities	$	568,263		$	443,135
Current federal income tax refundable	$	5,581		$	8,482
Current state income tax payable	$	774		$	294

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

	For the Years Ended December 31,
	2011			2010			2009
	(in thousands)
Federal statutory tax (expense) benefit	$	(118,652	)	$	(110,214	)	$	55,812
(Increase) decrease in tax resulting from:
State tax (expense) benefit (net of federal benefit)	(6,458		)	(7,750		)	5,141
Research and development credit	4,516			—			—
Change in valuation allowance	(1,627		)	1,039			(56		)
Statutory depletion	341			266			189
Other	(1,705		)	(1,400		)	(992		)
Income tax (expense) benefit	$	(123,585	)	$	(118,059	)	$	60,094

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

	For the Years Ended December 31,
	2011			2010			2009
	(in thousands)
Beginning balance	$	807		$	884		$	994
Additions based on tax positions related to current year	1,172			—			—
Additions for tax positions of prior years	183			244			231
Reductions for lapse of statute of limitations	(201		)	(321		)	(341		)
Ending balance	$	1,961		$	807		$	884