Condensed Consolidating Statement of Cash Flows (Detail) (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 (loss)	$ 149,426	$ 194,332	$ 96,429
Adjustments to reconcile net income (loss) 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 (benefit)	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 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)
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			(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
Repayment 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 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
Parent
Cash flows from operating activities:
Net income (loss)	149,426	194,332	96,429
Adjustments to reconcile net income (loss) to net cash provided by operating activities:
Depreciation, depletion and amortization	63,022	17,860	40,351
Accretion expense	561	15	14,503
Deferred income tax provision (benefit)	(56,175)	(1,403)	(28,569)
Settlement of asset retirement obligations			(6,461)
Non-cash stock compensation expense	8,699	5,905	5,692
Excess tax benefits	(949)	(1,493)	(299)
Non-cash derivative income			(324)
Loss on early extinguishment of debt	1,972	607	1,820
Non-cash interest expense	13,085	1,908	858
Other non-cash expense		(1,602)	979
Non-cash (income) loss from investment in subsidiaries	(223,555)	(230,861)	(140,366)
Change in current income taxes	10,618	(19,451)	(10,783)
Change in intercompany receivable/payables	275,819	217,287	349,118
(Increase) decrease in accounts receivable	(22,750)	(11,022)	(11,556)
(Increase) decrease in other current assets	(2,836)	(80)	18
Decrease in inventory	436	1,605	1,848
Increase (decrease) in accounts payable	5,348	2,658	(1,045)
Decrease in other current liabilities	(5,311)	23,440	(17,423)
Other	10,960	(1,628)	1,230
Net cash provided by (used in) operating activities	228,370	198,077	296,020
Cash flows from investing activities:
Investment in oil and gas properties	(324,542)	(309,026)	(265,198)
Proceeds from sale of oil and gas properties, net of expenses	403	5,575	25,455
Sale of fixed assets	134
Investment in fixed and other assets	(13,370)	(2,247)	(2,949)
Net cash used in investing activities	(337,375)	(305,698)	(242,692)
Cash flows from financing activities:
Proceeds from bank borrowings	25,000	75,000
Repayment 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 financing activities	300,014	39,895	(13,043)
Net change in cash and cash equivalents	191,009	(67,726)	40,285
Cash and cash equivalents, beginning of year	37,389	105,115	64,830
Cash and cash equivalents, end of year	228,398	37,389	105,115
Guarantor Subsidiary
Cash flows from operating activities:
Net income (loss)	223,555	232,751	140,366
Adjustments to reconcile net income (loss) to net cash provided by operating activities:
Depreciation, depletion and amortization	281,152	261,326	206,856
Accretion expense	32,513	30,385	19,524
Deferred income tax provision (benefit)	125,750	130,923	79,043
Settlement of asset retirement obligations	(65,567)	(63,391)	(30,440)
Non-cash derivative income	(509)	(2,216)
Non-cash (income) loss from investment in subsidiaries	75	(1,063)	337
Change in current income taxes			(88)
Change in intercompany receivable/payables	(275,125)	(217,724)	(347,941)
(Increase) decrease in accounts receivable	(33,345)	(7,688)	61,254
(Increase) decrease in other current assets		14	56
Decrease in inventory		14	275
Increase (decrease) in accounts payable	(208)	3,341	272
Decrease in other current liabilities	(5,115)	6,143	(665)
Other	(1,661)		68
Net cash provided by (used in) operating activities	281,515	372,815	128,917
Cash flows from investing activities:
Investment in oil and gas properties	(231,313)	(455,903)	(136,394)
Proceeds from sale of oil and gas properties, net of expenses		82,355	6,180
Acquisition of non-controlling interest			(1,007)
Net cash used in investing activities	(231,313)	(373,548)	(131,221)
Cash flows from financing activities:
Net change in cash and cash equivalents	50,202	(733)	(2,304)
Cash and cash equivalents, beginning of year	926	1,659	3,963
Cash and cash equivalents, end of year	51,128	926	1,659
Non-Guarantor Subsidiaries
Cash flows from operating activities:
Net income (loss)	(75)	(827)	(337)
Adjustments to reconcile net income (loss) to net cash provided by operating activities:
Depreciation, depletion and amortization	191	834	994
Accretion expense	257	364	442
Change in intercompany receivable/payables	(694)	437	(1,177)
(Increase) decrease in accounts receivable	224	(890)	(65)
Increase (decrease) in accounts payable	(39)	40
Net cash provided by (used in) operating activities	(136)	(42)	(143)
Cash flows from investing activities:
Investment in oil and gas properties		(4)	(175)
Net cash used in investing activities		(4)	(175)
Cash flows from financing activities:
Net change in cash and cash equivalents	(136)	(46)	(318)
Cash and cash equivalents, beginning of year	136	182	500
Cash and cash equivalents, end of year		136	182
Eliminations
Cash flows from operating activities:
Net income (loss)	(223,480)	(231,924)	(140,029)
Adjustments to reconcile net income (loss) to net cash provided by operating activities:
Non-cash (income) loss from investment in subsidiaries	$ 223,480	$ 231,924	$ 140,029