CONSOLIDATED STATEMENT OF CASH FLOWS (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Cash flows from operating activities:
Net income	$ 149,426	$ 194,332	$ 96,429
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation, depletion and amortization	344,365	280,020	248,201
Accretion expense	33,331	30,764	34,469
Deferred income tax provision	69,575	129,520	50,474
Settlement of asset retirement obligations	(65,567)	(63,391)	(36,901)
Non-cash stock compensation expense	8,699	5,905	5,692
Excess tax benefits	(949)	(1,493)	(299)
Non-cash derivative income	(509)	(2,216)	(324)
Loss on early extinguishment of debt	1,972	607	1,820
Non-cash interest expense	13,085	1,908	858
Other non-cash (income) expense		(1,602)	979
Change in current income taxes	10,618	(19,451)	(10,871)
(Increase) decrease in accounts receivable	(55,871)	(19,600)	49,633
(Increase) decrease in other current assets	(2,836)	(66)	74
Decrease in inventory	436	1,619	2,123
Increase (decrease) in accounts payable	5,101	6,039	(773)
Increase (decrease) in other current liabilities	(10,426)	29,583	(18,088)
Other	9,299	(1,628)	1,298
Net cash provided by (used in) operating activities	509,749	570,850	424,794
Cash flows from investing activities:
Investment in oil and gas properties	(555,855)	(764,933)	(401,767)
Proceeds from sale of oil and gas properties, net of expenses	403	87,930	31,635
Sale of fixed assets	134
Investment in fixed and other assets	(13,370)	(2,247)	(2,949)
Acquisition of non-controlling interest in subsidiary			(1,007)
Net cash used in investing activities	(568,688)	(679,250)	(374,088)
Cash flows from financing activities:
Proceeds from bank borrowings	25,000	75,000
Repayments of bank borrowings	(70,000)	(30,000)	(175,000)
Proceeds from issuance of senior convertible notes	300,000
Deferred financing costs of senior convertible notes	(8,855)
Proceeds from sold warrants	40,170
Payments for purchased call options	(70,830)
Proceeds from issuance of senior notes	300,000		375,000
Deferred financing costs	(11,966)	(4,017)	(11,474)
Redemption of senior subordinated notes	(200,681)		(200,503)
Excess tax benefits	949	1,493	299
Net payments for share based compensation	(3,773)	(2,581)	(1,365)
Net cash provided by (used in) financing activities	300,014	39,895	(13,043)
Net change in cash and cash equivalents	241,075	(68,505)	37,663
Cash and cash equivalents, beginning of year	38,451	106,956	69,293
Cash and cash equivalents, end of year	279,526	38,451	106,956
Cash (paid) refunded during the year for:
Interest, net of amount capitalized	(20,150)	(9,808)	(8,760)
Income taxes	$ (4,405)	$ 935	$ (26,525)