Statements of Cash Flows (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2012 Senior Notes 6.375% Due 2022	Dec. 31, 2011 Senior Notes 6.375% Due 2022	Dec. 31, 2010 Senior Notes 6.375% Due 2022
Cash flows from operating activities:
Net earnings (loss)	$ 171,539	$ (228,063)	$ 82,524
Depreciation, depletion and amortization	227,700	215,822	182,657
Gain on purchase	0	1,046	0
Extinguishment of debt	6,842	4,072	573
Amortization of debt issuance costs and net discount	7,031	8,243	8,481
Impairment of oil and natural gas properties	79	625,564	0
Dry hole and impairment	14,945	4,616	1,478
Derivatives	(36,135)	(29,094)	42,609
Stock-based compensation expense	9,819	9,636	9,386
Deferred income taxes	82,881	(149,279)	54,698
Gain on sale of assets	(1,782)	0	0
Other, net	(1,628)	1,420	(1,844)
Allowance for bad debt	414	0	0
Bad debt recovery	0	0	(38,508)
Change in book overdraft	(1,220)	(156)	528
Changes in operating assets and liabilities:
Accounts receivable	(6,740)	(23,526)	20,055
Inventories, prepaid expenses, and other current assets	(6,203)	(2,768)	(7,553)
Accounts payable and revenue and royalties payable	19,967	25,019	5,273
Accrued interest and other accrued liabilities	13,930	(4,561)	6,880
Net cash provided by operating activities	501,439	455,899	367,237
Cash flows from investing activities:
Exploration and development of oil and natural gas properties	(675,951)	(527,112)	(310,139)
Property acquisitions	(78,313)	(158,090)	(334,409)
Capitalized interest	(17,915)	(29,117)	(28,321)
Proceeds from sale of assets	17,307	0	0
Deposits on asset sales	(3,300)	3,300	0
Net cash used in investing activities	(758,172)	(711,019)	(672,869)
Cash flows from financing activities:
Proceeds from issuances on line of credit	0	406,600	316,000
Repayments of borrowings under line of credit	0	(411,900)	(310,700)
Net proceeds from Issuance long-term debt				600,000	0	0
Early Repayment of Subordinated Debt	(200,000)	0	0
Early Repayment of Senior Debt	149,999	94,744	0
Proceeds from long-term borrowings under credit facility	1,467,200	719,700	363,000
Repayments of long-term borrowings under credit facility	(1,435,800)	(358,200)	(565,000)
Financing obligation	(417)	(380)	(346)
Debt issuance costs	(11,424)	(2,250)	(15,173)
Dividends paid	(17,549)	(16,846)	(16,181)
Proceeds from issuance of stock	0	0	224,313
Proceeds from stock option exercises	3,687	10,113	4,402
Excess income tax benefit	1,049	3,047	284
Net cash provided by (used in) financing activities	256,747	255,140	300,599
Net increase (decrease) in cash and cash equivalents	14	20	(5,033)
Cash and cash equivalents at beginning of year	298	278	5,311
Cash and cash equivalents at end of year	312	298	278
Supplemental disclosures of cash flow information:
Interest paid, net of capitalized interest	64,602	59,853	40,773
Income Taxes Paid	4,227	7,914	697
Noncash investing activities:
Accrued capital expenditures	98,020	61,098	51,095
Asset retirement obligations	$ 18,248	$ 7,448	$ 3,721