Condensed Consolidated Statement of Cash Flows (Unaudited) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011
Debt Instrument [Line Items]
Financing costs of senior convertible notes	$ (8,855)	$ (66)
Cash flows from operating activities:
Net income	50,974	39,792
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation, depletion and amortization	84,575	67,669
Accretion expense	8,266	7,717
Deferred income tax provision	27,439	22,383
Settlement of asset retirement obligations	(2,980)	(19,034)
Non-cash stock compensation expense	1,750	1,680
Excess tax benefits	(847)	(649)
Non-cash derivative expense	1,342	1,804
Other non-cash expenses (income)	1,173	(104)
Change in current income taxes	(2,647)	(3,681)
Increase in accounts receivable	(21,708)	(21,555)
Decrease in other current assets	35	25
Decrease in inventory		365
Increase (decrease) in accounts payable	(6,015)	2,690
Decrease in other current liabilities	(22,168)	(10,059)
Other	146	272
Net cash provided by operating activities	119,335	89,315
Cash flows from investing activities:
Investment in oil and gas properties	(106,469)	(156,535)
Proceeds from sale of oil and gas properties		7,692
Sale of fixed assets	134
Investment in fixed and other assets	(909)	(262)
Net cash used in investing activities	(107,244)	(149,105)
Cash flows from financing activities:
Proceeds from bank borrowings	25,000
Repayments of bank borrowings	(70,000)
Proceeds from issuance of senior convertible notes	300,000
Proceeds from Sold Warrants	40,170
Payments for Purchased Call Options	(70,830)
Financing costs of senior convertible notes	(8,855)	(66)
Excess tax benefits	847	649
Net payments for share based compensation	(3,033)	(1,843)
Net cash provided by (used in) financing activities	213,299	(1,260)
Net change in cash and cash equivalents	225,390	(61,050)
Cash and cash equivalents, beginning of period	38,451	106,956
Cash and cash equivalents, end of period	263,841	45,906
Senior Convertible Notes
Debt Instrument [Line Items]
Financing costs of senior convertible notes	(8,855)
Cash flows from financing activities:
Financing costs of senior convertible notes	$ (8,855)