Consolidated Balance Sheets (USD $) In Thousands, unless otherwise specified	Mar. 31, 2012	Dec. 31, 2011
Assets, Current [Abstract]
Cash and Cash Equivalents, at Carrying Value	$ 2,533	$ 11,307
Restricted cash	121	121
Oil and gas revenue receivable	73,040	88,243
Oil and Gas Joint Interest Billing Receivables, Current	48,513	82,370
Derivative Assets, Current	289,078	230,385
Prepaid drilling costs and other current assets	13,691	7,494
Assets, Current	426,976	419,920
Oil And Gas Properties Net Using Full Cost Method Of Accounting [Abstract]
Proved	3,809,765	3,651,622
Unproved properties not being amortized	541,868	537,526
Property, Plant and Equipment, Net	266,597	246,586
Other Assets, Noncurrent	13,516	14,051
Assets	5,058,722	4,869,705
Liabilities, Current [Abstract]
Accounts payable and accrued liabilities	265,806	295,873
Production taxes payable	59,531	62,117
Interest Payable	8,777	30,306
Current deferred tax liability	97,275	73,380
Derivative Liabilities, Current	946	0
Capital cost accrual	195,164	209,303
Liabilities, Current	627,499	670,979
Long-term Debt, Excluding Current Maturities	2,019,000	1,903,000
Deferred Tax Liabilities, Noncurrent	658,927	635,009
Other Liabilities, Noncurrent	80,885	67,008
Commitments and Contingencies
Stockholders' Equity Attributable to Parent [Abstract]
Common Stock, Value, Issued	462,988	463,221
Treasury Stock, Value	(484)	(14,951)
Retained Earnings (Accumulated Deficit)	1,209,907	1,145,439
Stockholders' Equity Attributable to Parent	1,672,411	1,593,709
Liabilities and Stockholders' Equity	$ 5,058,722	$ 4,869,705