Income Taxes (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Components of the provision for income taxes
Federal	$ 0	$ 0	$ 0
State	1,571	868	2,121
Deferred portion of income tax expense (benefit)	(276,722)	397,780	105,555
Income tax expense (benefit)	$ (275,151)	$ 398,648	$ 107,676
Effective tax rate (as a percent)	38.10%	37.40%	38.60%
Deferred Income Taxes [Abstract]
Deferred Tax Liabilities, Oil and Gas Properties	$ 854,029	$ 1,029,424
Deferred Tax Liabilities, Derivative asset	179,543	220,437
Deferred Tax Liabilities, Other	1,233	4,475
Deferred Tax Liabilities	1,034,805	1,254,336
Deferred Tax Assets, Federal and State Tax Net Operating Loss Carryforwards	244,942	184,447
Deferred Tax Assets, Tax Deferred Expense, Compensation and Benefits, Share-based Compensation Cost	14,529	16,763
Deferred Tax Assets, Other Liabilities	27,449	25,715
Deferred Tax Assets, Gross	286,920	226,925
Deferred Tax Assets, Valuation Allowance	(10,394)	(7,246)
Deferred Tax Assets, Net	276,526	219,679
Deferred Tax Liabilities, Net	758,279	1,034,657
Unrecognized Tax Benefits, Exercise of Stock Awards	126,700
Income Tax Expense (Benefit), Continuing Operations, Income Tax Reconciliation [Abstract]
Federal statutory tax expense (benefit)	(253,001)	372,644	$ 97,514
State tax expense (benefit) (net of federal benefit)	(21,583)	21,350	9,400
Change in valuation allowance	3,148	2,245	(314)
Research and development credit	(1,971)	0	0
Other	(1,744)	2,409	1,076
Tax Credit Recorded for IRS R&D Settlement	2,000
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Unrecognized Tax Benefits, Beginning Balance	1,582	2,358	2,278
Unrecognized Tax Benefits, Additions For Tax Positions Of Prior Years	1,200	140	80
Unrecognized Tax Benefits, Decrease Resulting from Settlements with Taxing Authorities	0	(916)	0
Unrecognized Tax Benefits, Ending Balance	2,782	1,582	$ 2,358
Internal Revenue Service (IRS) [Member]
Deferred Income Taxes [Abstract]
Income Taxes Receivable, Current	5,378	4,734
Operating Loss Carryforwards	796,700
State and Local Jurisdiction [Member]
Deferred Income Taxes [Abstract]
Income Taxes Receivable, Current	65	0
Taxes Payable, Current	0	$ 25
Operating Loss Carryforwards	338,900
Minimum [Member]
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Increase in Unrecognized Tax Benefits is Reasonably Possible	0
Decrease in Unrecognized Tax Benefits is Reasonably Possible	0
Maximum [Member]
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Increase in Unrecognized Tax Benefits is Reasonably Possible	1,800
Decrease in Unrecognized Tax Benefits is Reasonably Possible	1,800
Internal Revenue Service (IRS) [Member] | Research Tax Credit Carryforward [Member] | Domestic Tax Authority [Member]
Deferred Income Taxes [Abstract]
Tax Credit Carryforward, Amount	$ 7,200