Condensed Consolidated Statements Of Cash Flows (USD $) In Thousands, unless otherwise specified	9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012
OPERATING ACTIVITIES:
Net income	$ 133,445	$ 79,723
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation, depletion, and amortization	242,590	234,350
Impairment of oil and natural gas properties (Note 2)	0	115,874
Loss on derivatives	1,765	4,621
Deferred tax expense	77,566	50,677
Gain on disposition of assets	(7,744)	(1,283)
Stock compensation plans	16,652	12,271
Other, net	4,263	3,376
Changes in operating assets and liabilities increasing (decreasing) cash:
Accounts receivable	1,888	4,516
Accounts payable	320	(11,753)
Material and supplies	(1,767)	(1,949)
Accrued liabilities	31,041	23,195
Other, net	942	(1,478)
Net cash provided by operating activities	500,961	512,140
INVESTING ACTIVITIES:
Capital expenditures	(512,574)	(584,858)
Producing property and other acquisitions (Note 3)	0	(600,321)
Proceeds from disposition of assets	89,916	296,582
Net cash used in investing activities	(422,658)	(888,597)
FINANCING ACTIVITIES:
Borrowings under credit agreement	222,500	543,700
Payments under credit agreement	(293,600)	(593,700)
Proceeds from issuance of senior subordinated notes, net of debt issuance costs and discount	0	386,274
Proceeds from exercise of stock options	578	90
Book overdrafts	(7,014)	40,281
Net cash provided by (used in) financing activities	(77,536)	376,645
Net increase in cash and cash equivalents	767	188
Cash and cash equivalents, beginning of period	974	835
Cash and cash equivalents, end of period	1,741	1,023
Supplemental disclosure of cash flow information:
Changes in accounts payable and accrued liabilities related to purchases of property, plant, and equipment	(516)	26,477
Non-cash additions (reductions) to oil and natural gas properties related to asset retirement obligations	$ (16,417)	$ 45,188