Condensed Consolidated Statements of Cash Flows (USD $) In Thousands, unless otherwise specified	6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012
Cash flows from operating activities:
Net income	$ 219,492	$ 170,409
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation, depletion and amortization	283,669	239,499
Asset retirement obligation	5,283	5,966
Deferred income taxes	129,792	101,080
Stock compensation	7,112	9,218
Derivative instruments, net	(10,292)	(5,990)
Loss on early extinguishment of debt		16,214
Changes in non-current assets and liabilities	5,790	5,115
Other, net	(2,116)	1,955
Changes in operating assets and liabilities:
(Increase) decrease in receivables, net	(55,060)	107,834
(Increase) decrease in other current assets	14,840	(4,910)
(Decrease) in accounts payable and accrued liabilities	(28,724)	(71,458)
Net cash provided by operating activities	569,786	574,932
Cash flows from investing activities:
Oil and gas expenditures	(776,138)	(758,608)
Sales of oil and gas assets	14,407	1,273
Sales of other assets	31,157	408
Other expenditures	(25,475)	(26,087)
Net cash used by investing activities	(756,049)	(783,014)
Cash flows from financing activities:
Net increase (decrease) in bank debt	142,000	(55,000)
Increase in other long-term debt		750,000
Decrease in other long-term debt		(363,595)
Financing costs incurred		(12,692)
Dividends paid	(22,448)	(18,869)
Issuance of common stock and other	1,705	2,764
Net cash provided by financing activities	121,257	302,608
Net change in cash and cash equivalents	(65,006)	94,526
Cash and cash equivalents at beginning of period	69,538	2,406
Cash and cash equivalents at end of period	$ 4,532	$ 96,932