Guarantor Financial Statements (Details 2) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2010	Sep. 30, 2010	Jun. 30, 2010	Mar. 31, 2010	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Cash flows from operating activities:
Net income (loss)	$ 45,523	$ 51,821	$ 57,196	$ 39,792	$ 23,757	$ 19,382	$ 27,872	$ 25,418	$ 194,332	$ 96,429	$ (218,271)
Adjustments to reconcile net income (loss) to net cash provided by operating activities:
Depreciation, depletion and amortization									280,020	248,201	259,639
Write-down of oil and gas properties											508,989
Accretion expense									30,764	34,469	39,306
Deferred income tax provision (benefit)									129,520	50,474	(146,935)
Settlement of asset retirement obligations									(63,391)	(36,901)	(66,780)
Non-cash stock compensation expense									5,905	5,692	5,944
Excess tax benefits									(1,493)	(299)	(2)
Non-cash derivative (income) expense									(2,216)	(324)	5,142
Loss on early extinguishment of debt									607	1,820
Other non-cash expenses									306	1,837	10,971
Change in current income taxes									(19,451)	(10,871)	66,185
(Increase) decrease in accounts receivable									(19,600)	49,633	50,159
(Increase) decrease in other current assets									(66)	74	627
Decrease in inventory									1,619	2,123	17,561
Increase (decrease) in accounts payable									6,039	(773)	(10,200)
Increase (decrease) in other current liabilities									29,583	(18,088)	(14,431)
Other									(1,628)	1,298	(117)
Net cash provided by operating activities									570,850	424,794	507,787
Cash flows from investing activities:
Investment in oil and gas properties									(764,933)	(401,767)	(320,214)
Proceeds from sale of oil and gas properties, net of expenses									87,930	31,635	5,553
Investment in fixed and other assets									(2,247)	(2,949)	(1,412)
Sale of fixed assets											35
Acquisition of non-controlling interest										(1,007)	(41)
Net cash used in investing activities									(679,250)	(374,088)	(316,079)
Cash flows from financing activities:
Proceeds from bank borrowings									75,000
Repayments of bank borrowings									(30,000)	(175,000)	(250,000)
Redemption of senior subordinated notes										(200,503)
Proceeds from issuance of senior notes										375,000
Proceeds (Expenses) from stock offering											60,447
Deferred financing costs									(4,017)	(11,474)	(141)
Excess tax benefits									1,493	299	2
Purchase of treasury stock											(347)
Net payments for share based compensation									(2,581)	(1,365)	(513)
Net cash provided by (used in) financing activities									39,895	(13,043)	(190,552)
Net increase (decrease) in cash and cash equivalents									(68,505)	37,663	1,156
Cash and cash equivalents, beginning of year				106,956				69,293	106,956	69,293	68,137
Cash and cash equivalents, end of year	38,451				106,956				38,451	106,956	69,293
Parent [Member]
Cash flows from operating activities:
Net income (loss)									194,332	96,429	(218,298)
Adjustments to reconcile net income (loss) to net cash provided by operating activities:
Depreciation, depletion and amortization									17,860	40,351	47,695
Write-down of oil and gas properties											3,849
Accretion expense									15	14,503	16,058
Deferred income tax provision (benefit)									(1,403)	(28,569)	(2,657)
Settlement of asset retirement obligations										(6,461)	(9,364)
Non-cash stock compensation expense									5,905	5,692	5,944
Excess tax benefits									(1,493)	(299)	(2)
Non-cash derivative (income) expense										(324)	5,142
Loss on early extinguishment of debt									607	1,820
Non-cash (income) loss from investment in subsidiaries									(232,751)	(140,366)	268,011
Other non-cash expenses									306	1,837	9,915
Change in current income taxes									(19,451)	(10,783)	64,481
Change in intercompany receivable/payables									217,287	349,118
(Increase) decrease in accounts receivable									(11,022)	(11,556)	177,984
(Increase) decrease in other current assets									(80)	18	585
Decrease in inventory									1,605	1,848	16,478
Increase (decrease) in accounts payable									2,658	(1,045)	(5,652)
Increase (decrease) in other current liabilities									23,440	(17,423)	(19,448)
Other									(1,628)	1,230	739
Net cash provided by operating activities									198,077	296,020	361,460
Cash flows from investing activities:
Investment in oil and gas properties									(309,026)	(265,198)	(177,341)
Proceeds from sale of oil and gas properties, net of expenses									5,575	25,455	5,553
Investment in fixed and other assets									(2,247)	(2,949)	(1,412)
Net cash used in investing activities									(305,698)	(242,692)	(173,200)
Cash flows from financing activities:
Proceeds from bank borrowings									75,000
Repayments of bank borrowings									(30,000)	(175,000)	(250,000)
Redemption of senior subordinated notes										(200,503)
Proceeds from issuance of senior notes										375,000
Proceeds (Expenses) from stock offering											60,447
Deferred financing costs									(4,017)	(11,474)	(141)
Excess tax benefits									1,493	299	2
Purchase of treasury stock											(347)
Net payments for share based compensation									(2,581)	(1,365)	(513)
Net cash provided by (used in) financing activities									39,895	(13,043)	(190,552)
Net increase (decrease) in cash and cash equivalents									(67,726)	40,285	(2,292)
Cash and cash equivalents, beginning of year				105,115				64,830	105,115	64,830	67,122
Cash and cash equivalents, end of year	37,389				105,115				37,389	105,115	64,830
Guarantor Subsidiary [Member]
Cash flows from operating activities:
Net income (loss)									232,751	140,366	(268,011)
Adjustments to reconcile net income (loss) to net cash provided by operating activities:
Depreciation, depletion and amortization									261,326	206,856	211,465
Write-down of oil and gas properties											505,140
Accretion expense									30,385	19,524	23,203
Deferred income tax provision (benefit)									130,923	79,043	(144,278)
Settlement of asset retirement obligations									(63,391)	(30,440)	(57,416)
Non-cash derivative (income) expense									(2,216)
Non-cash (income) loss from investment in subsidiaries									827	337	3
Other non-cash expenses											1,056
Change in current income taxes										(88)	1,704
Change in intercompany receivable/payables									(217,724)	(347,941)
(Increase) decrease in accounts receivable									(7,688)	61,254	(127,809)
(Increase) decrease in other current assets									14	56	42
Decrease in inventory									14	275	1,083
Increase (decrease) in accounts payable									3,341	272	(3,787)
Increase (decrease) in other current liabilities									6,143	(665)	5,017
Other										68	(856)
Net cash provided by operating activities									372,815	128,917	146,556
Cash flows from investing activities:
Investment in oil and gas properties									(455,903)	(136,394)	(143,405)
Proceeds from sale of oil and gas properties, net of expenses									82,355	6,180
Sale of fixed assets											35
Acquisition of non-controlling interest										(1,007)	(41)
Net cash used in investing activities									(373,548)	(131,221)	(143,411)
Cash flows from financing activities:
Net increase (decrease) in cash and cash equivalents									(733)	(2,304)	3,145
Cash and cash equivalents, beginning of year				1,659				3,963	1,659	3,963	818
Cash and cash equivalents, end of year	926				1,659				926	1,659	3,963
Non-Guarantor Subsidiaries [Member]
Cash flows from operating activities:
Net income (loss)									(827)	(337)	24
Adjustments to reconcile net income (loss) to net cash provided by operating activities:
Depreciation, depletion and amortization									834	994	479
Accretion expense									364	442	45
Change in intercompany receivable/payables									437	(1,177)
(Increase) decrease in accounts receivable									(890)	(65)	440
Increase (decrease) in accounts payable									40		(761)
Net cash provided by operating activities									(42)	(143)	227
Cash flows from investing activities:
Investment in oil and gas properties									(4)	(175)	76
Net cash used in investing activities									(4)	(175)	76
Cash flows from financing activities:
Net increase (decrease) in cash and cash equivalents									(46)	(318)	303
Cash and cash equivalents, beginning of year				182				500	182	500	197
Cash and cash equivalents, end of year	136				182				136	182	500
Eliminations [Member]
Cash flows from operating activities:
Net income (loss)									(231,924)	(140,029)	268,014
Adjustments to reconcile net income (loss) to net cash provided by operating activities:
Non-cash (income) loss from investment in subsidiaries									231,924	140,029	(268,014)
(Increase) decrease in accounts receivable											(456)
Net cash provided by operating activities											(456)
Cash flows from investing activities:
Investment in oil and gas properties											456
Net cash used in investing activities											456
Cash flows from financing activities:
Cash and cash equivalents, beginning of year				0					0
Cash and cash equivalents, end of year	$ 0				$ 0				$ 0	$ 0