Income Taxes (Details) (USD $)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
IRS Proposed R&D Tax Adjustment	$ 4,600,000
Excess tax benefit	0	0	0
Income Tax Examination, Liability (Refund) Adjustment from Settlement with Taxing Authority	4,000,000
Current portion of income tax expense (benefit):
Federal	0	0	(1,757,000)
State	2,121,000	370,000	1,553,000
Deferred portion of income tax expense (benefit)	(105,555,000)	29,638,000	(123,789,000)
Income tax (expense) benefit	107,676,000	(29,268,000)	123,585,000
Effective tax rate (as a percent)	38.60%	35.00%	36.50%
Excess income tax benefit from the exercise of stock awards	0
Deferred Income Taxes [Abstract]
Deferred Tax Liabilities, Oil and Gas Properties	768,463,000	678,624,000
Deferred Tax Liabilities, Derivative asset	9,529,000	15,942,000
Deferred Tax Liabilities, Other	1,245,000	6,443,000
Deferred Tax Liabilities	779,237,000	701,009,000
Deferred Tax Assets, Federal and state tax net operating loss carryovers	91,788,000	113,522,000
Deferred Tax Assets, Net Profits Plan Liability	20,913,000	29,233,000
Deferred Tax Assets, Stock compensation	18,820,000	18,026,000
Deferred Tax Assets, Other Long-term Liabilities	13,341,000	16,739,000
Deferred Tax Assets, Gross	144,862,000	177,520,000
Deferred Tax Assets, Valuation Allowance	(5,001,000)	(5,315,000)
Deferred Tax Assets, Net	139,861,000	172,205,000
Deferred Tax Liabilities, Net	639,376,000	528,804,000
Less: current deferred income tax liabilities	(172,000)	(5,442,000)
Add: current deferred income tax assets	10,921,000	14,021,000
Deferred income taxes; Net, non-current	650,125,000	537,383,000
Income Taxes Receivable, Current	4,630,000	3,364,000
Deferred Tax Assets, Operating Loss Carryforwards, Domestic	376,100,000
Unrecognized Tax Benefits, Exercise of Stock Awards	126,700,000
Deferred Tax Assets, Operating Loss Carryforwards, State and Local	147,500,000
Deferred Tax Assets, Tax Credit Carryforwards, Research	5,000,000
Income Tax Expense (Benefit), Continuing Operations, Income Tax Reconciliation [Abstract]
Federal statutory tax expense (benefit)	97,514,000	(29,231,000)	118,652,000
State tax expense (benefit) (net of federal benefit)	9,400,000	(992,000)	6,458,000
Research and development credit	0	(970,000)	(4,516,000)
Change in valuation allowance	(314,000)	1,524,000	1,627,000
Statutory depletion	(154,000)	(210,000)	(341,000)
Other	1,230,000	611,000	1,705,000
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Unrecognized Tax Benefits, Beginning Balance	2,278,000	1,961,000	807,000
Unrecognized Tax Benefits, Additions based on tax positions related to current year	0	0	1,172,000
Unrecognized Tax Benefits, Additions For Tax Positions Of Prior Years	80,000	317,000	183,000
Unrecognized Tax Benefits,Reductions For Lapse Of Statute Of Limitations	0	0	(201,000)
Unrecognized Tax Benefits, Ending Balance	2,358,000	2,278,000	1,961,000
Internal Revenue Service (IRS) [Member]
Deferred Income Taxes [Abstract]
Income Taxes Receivable, Current	4,630,000	2,511,000
State and Local Jurisdiction [Member]
Deferred Income Taxes [Abstract]
Income Taxes Receivable, Current	0	853,000
Taxes Payable, Current	1,460,000	0
Unrecognized Tax Benefit Possible Change, Minimum [Member]
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Unrecognized Tax Benefits, Ending Balance	0
Unrecognized Tax Benefit Possible Change, Maximum [Member]
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Unrecognized Tax Benefits, Ending Balance	$ 1,400,000