Statement of Cash Flows (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
OPERATING ACTIVITIES:
Net income	$ 23,176	$ 195,867	$ 146,484
Adjustments to reconcile net income (loss) to net cash provided by (used) by operating activities:
Depreciation, depletion, amortization, and impairment	319,021	280,451	205,124
Impairment of oil and natural gas properties (Note 2)	283,606	0	0
Unrealized (gain) loss on derivatives	1,243	(2,413)	(1,036)
(Gain) loss on disposition of assets	(253)	595	(9,687)
Deferred tax expense	15,530	125,551	100,672
Employee stock compensation plans	16,956	14,303	10,067
Bad debt expense	90	260	0
ARO liability accretion	4,615	3,838	2,937
Other, net	781	294	(69)
Changes in operating assets and liabilities increasing (decreasing) cash:
Accounts receivable	13,994	(38,731)	(58,965)
Materials and supplies	(361)	(1,886)	598
Prepaid expenses and other	(3,466)	22,672	6,957
Accounts payable	10,187	(1,064)	(8,913)
Accrued liabilities	6,911	9,245	(3,555)
Contract advances	(1,119)	(527)	(542)
Net cash provided by operating activities	690,911	608,455	390,072
INVESTING ACTIVITIES:
Capital expeditures	(762,381)	(728,551)	(484,080)
Producing property and other acquisitions	(598,485)	(50,013)	(92,229)
Proceeds from disposition of property and equipment	281,824	10,328	40,048
Net cash used in investing activities	(1,079,042)	(768,236)	(536,261)
FINANCING ACTIVITIES:
Borrowings under line of credit	735,300	441,500	286,900
Payments under line of credit	(714,200)	(554,500)	(153,900)
Proceeds from issuance of senior subordinated notes, net of debt issuance costs and discount	386,274	243,950	0
Proceeds from exercise of stock options	215	679	149
Tax benefit from stock options	121	1,174	40
Increase (decrease) in book overdrafts (Note 2)	(19,440)	26,454	13,219
Net cash provided by financing activities	388,270	159,257	146,408
Net increase (decrease) in cash and cash equivalents	139	(524)	219
Cash and cash equivalents, beginning of year	835	1,359
Cash and cash equivalents, end of year	974	835	1,359
Supplemental disclosure of cash flow information:
Interest paid (net of capitalization)	14,880	3,470	0
Income taxes	5,116	655	3,143
Changes in accounts payable and accrued liabilites related to purchases of property, plant, and equipment	(4,753)	(28,036)	(29,700)
Non-cash additions to oil and natural gas properties related to asset retirement obligations	$ 45,097	$ 23,345	$ 9,924