Consolidated Balance Sheets (USD $) In Thousands	Sep. 30, 2011	Dec. 31, 2010
Assets, Current [Abstract]
Cash and Cash Equivalents, at Carrying Value	$ 12,309	$ 70,834
Restricted cash	109	98
Oil and gas revenue receivable	90,774	95,142
Oil and Gas Joint Interest Billing Receivables, Current	75,258	48,561
Derivative Assets, Current	146,510	133,991
Inventory, Net	1,548	2,760
Prepaid drilling costs and other current assets	8,160	9,663
Assets, Current	334,668	361,049
Oil And Gas Properties Net Using Full Cost Method Of Accounting [Abstract]
Proved	3,411,536	2,589,423
Unproved properties not being amortized	526,579	486,247
Property, Plant and Equipment, Net	180,997	149,104
Derivative Assets, Noncurrent	17,149	2,066
Other Assets, Noncurrent	7,103	7,726
Assets	4,478,032	3,595,615
Liabilities, Current [Abstract]
Accounts payable and accrued liabilities	239,681	210,311
Current portion of long term debt	278,000	0
Production taxes payable	61,585	53,382
Interest Payable	8,175	26,878
Taxes Payable, Current	44,617	42,685
Derivative Liabilities, Current	0	718
Capital cost accrual	156,610	84,042
Liabilities, Current	788,668	418,016
Long-term Debt, Excluding Current Maturities	1,560,000	1,560,000
Deferred Tax Liabilities, Noncurrent	588,903	420,711
Derivative Liabilities, Noncurrent	0	5,337
Other Liabilities, Noncurrent	76,992	52,575
Stockholders' Equity Attributable to Parent [Abstract]
Common Stock, Value, Issued	457,411	426,779
Treasury Stock, Value	(7,694)
Retained Earnings (Accumulated Deficit)	1,013,752	712,197
Stockholders' Equity Attributable to Parent	1,463,469	1,138,976
Liabilities and Stockholders' Equity	$ 4,478,032	$ 3,595,615