Condensed Statements of Cash Flows (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Cash flows from operating activities:
Net earnings	$ 32,434	$ 33,898
Depreciation, depletion and amortization	68,478	48,422
Gain on sale of assets	(23)	(1,763)
Amortization of debt issuance costs and net discount	1,709	2,037
Impairment of oil and natural gas properties	2,467	0
Dry hole and impairment	449	28
Derivatives	3,146	42,837
Stock-based compensation expense	3,195	3,104
Deferred income taxes	19,648	16,567
Other, net	2,381	683
Allowance for bad debt	0	315
Change in book overdraft	(232)	(509)
Changes in operating assets and liabilities:
Accounts receivable	(9,507)	(7,835)
Inventories, prepaid expenses, and other current assets	(3,057)	(2,686)
Accounts payable and revenue and royalties payable	(25,411)	(674)
Accrued interest and other accrued liabilities	(3,979)	20,982
Net cash provided by operating activities	91,698	155,406
Cash flows from investing activities:
Exploration and development of oil and natural gas properties	(174,663)	(167,758)
Property acquisitions	(2,897)	(8,529)
Capitalized interest	(1,799)	(5,190)
Proceeds from sale of assets	480	15,700
Deposits on asset sales	0	(3,300)
Net cash used in investing activities	(178,879)	(169,077)
Cash flows from financing activities:
Long-term borrowings under credit facility	299,200	102,700
Repayments of long-term borrowings under credit facility	(208,500)	(634,200)
Financing obligation	(112)	(101)
Debt issuance costs	0	(10,569)
Dividends paid	(4,400)	(4,381)
Stock options and restricted stock issued	65	3,498
Excess income tax benefit	721	422
Net cash provided by financing activities	86,974	57,369
Net (decrease) increase in cash and cash equivalents	(207)	43,698
Cash and cash equivalents at beginning of period	312	298
Cash and cash equivalents at end of period	105	43,996
Noncash investing activities:
Accrued capital expenditures	32,379	41,339
Asset retirement obligations	7,022	4,994
6.375% Senior notes due 2022
Cash flows from financing activities:
Proceeds from issuance of 6.375% Senior notes due 2022	$ 0	$ 600,000