Guarantor Financial Statements (Details 2) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Cash flows from operating activities:
Net income	$ 30,547	$ 57,196	$ 81,521	$ 96,988
Adjustments to reconcile net income (loss) to net cash provided by operating activities:
Depreciation, depletion and amortization	87,133	72,646	171,708	140,315
Accretion expense	8,255	7,717	16,521	15,434
Deferred income tax provision	19,035	35,281	46,474	57,664
Settlement of asset retirement obligations			(21,918)	(33,568)
Non-cash stock compensation expense			4,271	3,138
Excess tax benefits			(795)	(1,060)
Non-cash derivative income			(2,758)	(118)
Loss on early extinguishment of debt				607
Non-cash interest expense			5,278	959
Change in current income taxes			(3,921)	(6,245)
Increase in accounts receivable			(37,517)	(37,428)
Increase in other current assets			(124)	(476)
Decrease in inventory			36	1,163
Increase in accounts payable			8,413	5,854
Decrease in other current liabilities			(17,304)	4,440
Other			(465)	(1,135)
Net cash provided by operating activities			249,420	246,532
Cash flows from investing activities:
Investment in oil and gas properties			(275,813)	(272,451)
Proceeds from sale of oil and gas properties, net of expenses			403	6,692
Sale of fixed assets			149
Investment in fixed and other assets			(1,900)	(894)
Net cash used in investing activities			(277,161)	(266,653)
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
Financing costs of senior convertible notes			(8,855)
Proceeds from Sold Warrants			40,170
Payments for Purchased Call Options			(70,830)
Deferred financing costs				(4,017)
Excess tax benefits			795	1,060
Net payments for share based compensation			(3,141)	(1,857)
Net cash provided by (used in) financing activities			213,139	(4,814)
Net change in cash and cash equivalents			185,398	(24,935)
Cash and cash equivalents, beginning of period			38,451	106,956
Cash and cash equivalents, end of period	223,849	82,021	223,849	82,021
Parent [Member]
Cash flows from operating activities:
Net income	30,547	57,196	81,521	96,988
Adjustments to reconcile net income (loss) to net cash provided by operating activities:
Depreciation, depletion and amortization	15,071	(24)	26,548	5,918
Accretion expense	137	4	285	8
Deferred income tax provision	(10,391)	(4,136)	(20,154)	(11,747)
Non-cash stock compensation expense			4,271	3,138
Excess tax benefits			(795)	(1,060)
Loss on early extinguishment of debt				607
Non-cash interest expense				(116,944)
Non-cash interest expense			5,278	959
Change in current income taxes			(3,921)	(3,893)
Change in intercompany receivable/payables			142,965	149,716
Increase in accounts receivable			(36,705)	(15,198)
Increase in other current assets			(124)	(491)
Decrease in inventory			36	1,149
Increase in accounts payable			5,238	2,494
Decrease in other current liabilities			(12,924)	(224)
Other			(118,152)	(21)
Net cash provided by operating activities			73,367	111,399
Cash flows from investing activities:
Investment in oil and gas properties			(129,792)	(134,792)
Proceeds from sale of oil and gas properties, net of expenses			403	5,575
Sale of fixed assets			149
Investment in fixed and other assets			(1,900)	(894)
Net cash used in investing activities			(131,140)	(130,111)
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
Financing costs of senior convertible notes			(8,855)
Proceeds from Sold Warrants			40,170
Payments for Purchased Call Options			(70,830)
Deferred financing costs				(4,017)
Excess tax benefits			795	1,060
Net payments for share based compensation			(3,141)	(1,857)
Net cash provided by (used in) financing activities			213,139	(4,814)
Net change in cash and cash equivalents			155,366	(23,526)
Cash and cash equivalents, beginning of period			37,389	105,115
Cash and cash equivalents, end of period	192,755	81,589	192,755	81,589
Guarantor Subsidiary [Member]
Cash flows from operating activities:
Net income	52,312	63,621	118,450	116,944
Adjustments to reconcile net income (loss) to net cash provided by operating activities:
Depreciation, depletion and amortization	71,969	72,426	144,969	133,936
Accretion expense	8,033	7,622	16,065	15,244
Deferred income tax provision	29,426	39,417	66,628	69,411
Settlement of asset retirement obligations			(21,918)	(33,568)
Non-cash derivative income			(2,758)	(118)
Non-cash interest expense				291
Change in current income taxes				(2,352)
Change in intercompany receivable/payables			(142,720)	(149,290)
Increase in accounts receivable			(833)	(22,239)
Increase in other current assets				15
Decrease in inventory				14
Increase in accounts payable			3,214	3,360
Decrease in other current liabilities			(4,380)	4,664
Other			(663)	(1,114)
Net cash provided by operating activities			176,054	135,198
Cash flows from investing activities:
Investment in oil and gas properties			(146,022)	(137,655)
Proceeds from sale of oil and gas properties, net of expenses				1,117
Net cash used in investing activities			(146,022)	(136,538)
Cash flows from financing activities:
Net change in cash and cash equivalents			30,032	(1,340)
Cash and cash equivalents, beginning of period			926	1,659
Cash and cash equivalents, end of period	30,958	319	30,958	319
Non-Guarantor Subsidiaries [Member]
Cash flows from operating activities:
Net income	141	(162)	(99)	(291)
Adjustments to reconcile net income (loss) to net cash provided by operating activities:
Depreciation, depletion and amortization	93	244	191	461
Accretion expense	85	91	171	182
Change in intercompany receivable/payables			(245)	(426)
Increase in accounts receivable			21	9
Increase in accounts payable			(39)
Other			(1)
Net cash provided by operating activities			(1)	(65)
Cash flows from investing activities:
Investment in oil and gas properties			1	(4)
Net cash used in investing activities			1	(4)
Cash flows from financing activities:
Net change in cash and cash equivalents				(69)
Cash and cash equivalents, beginning of period			136	182
Cash and cash equivalents, end of period	136	113	136	113
Eliminations [Member]
Cash flows from operating activities:
Net income	(52,453)	(63,459)	(118,351)	(116,653)
Adjustments to reconcile net income (loss) to net cash provided by operating activities:
Non-cash interest expense				116,653
Other			118,351
Cash flows from investing activities:
Proceeds from sale of oil and gas properties, net of expenses			403
Cash flows from financing activities:
Cash and cash equivalents, beginning of period
Cash and cash equivalents, end of period