Consolidated Balance Sheets - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Assets, Current [Abstract]
Cash and cash equivalents	$ 5,381	$ 8,919
Restricted cash	115	117
Oil and gas revenue receivable	75,485	111,915
Joint interest billing and other receivables	21,613	32,502
Derivative assets	55,425	104,190
Other current assets	11,691	19,495
Assets, Current	169,710	277,138
Oil And Gas Properties Net Using Full Cost Method Of Accounting [Abstract]
Proven	3,731,375	3,636,643
Unproven properties not being amortized	240,598	242,294
Property, plant and equipment, net	9,762	12,186
Deferred tax assets	15,756	30,640
Deferred financing costs and other	27,224	26,789
Assets	4,194,425	4,225,690
Liabilities, Current [Abstract]
Accounts payable	61,762	77,580
Accrued liabilities	52,821	89,865
Current portion of long term debt	62,000	100,000
Production taxes payable	58,824	55,585
Interest payable	42,659	46,098
Taxes Payable, Current	15,754	30,638
Derivative Liabilities, Current	0	0
Capital cost accrual	30,336	45,952
Liabilities, Current	324,156	445,718
Long-term debt	3,368,000	3,278,000
Deferred gain on sale of liquids gathering system	131,572	136,848
Deferred tax liabilities	465	992
Other long-term obligations	$ 155,906	$ 152,472
Commitments and contingencies
Stockholders' Equity Attributable to Parent [Abstract]
Common Stock, Value, Issued	$ 500,547	$ 495,913
Treasury Stock, Value	(337)	(6,213)
Retained loss	(285,884)	(278,040)
Total shareholders' deficit	214,326	211,660
Liabilities and Stockholders' Equity	$ 4,194,425	$ 4,225,690