Guarantor Financial Statements - Condensed Consolidating Statement of Cash Flows (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Cash flows from operating activities:
Net income (loss)	$ (152,906)	$ 4,444	$ (480,294)	$ 30,387
Adjustments to reconcile net income (loss) to net cash provided by operating activities:
Depreciation, depletion and amortization	77,951	92,835	164,373	175,481
Write-down of oil and gas properties	224,294		715,706
Accretion expense	6,408	7,733	12,817	15,288
Deferred income tax (benefit) provision	(85,048)	2,992	(264,954)	18,094
Settlement of asset retirement obligations			(35,923)	(24,915)
Non-cash stock compensation expense			6,028	5,358
Non-cash derivative expense			7,931	2,697
Non-cash interest expense			8,737	8,229
Change in current income taxes			7,206	(6)
(Increase) decrease in accounts receivable			23,047	(25,524)
Increase in other current assets			(1,959)	(82)
Increase (decrease) in accounts payable			(7,826)	1,843
Increase (decrease) in other current liabilities			(8,720)	50,785
Other			(504)	(675)
Net cash (used in) provided by operating activities			145,665	256,960
Cash flows from investing activities:
Investment in oil and gas properties			(264,355)	(517,904)
Proceeds from sale of oil and gas properties, net of expenses			10,100	51,955
Investment in fixed and other assets			(727)	(3,896)
Change in restricted funds			179,475	(356)
Net cash provided by (used in) investing activities			(75,507)	(470,201)
Cash flows from financing activities:
Proceeds from bank borrowings			5,000
Net proceeds from issuance of common stock				226,036
Repayments of bank borrowings			(5,000)
Deferred financing costs				(3,167)
Net payments for share-based compensation			(3,069)	(6,948)
Net cash provided by (used in) financing activities			(3,069)	215,921
Effect of exchange rate changes on cash			78	(18)
Net change in cash and cash equivalents			67,167	2,662
Cash and cash equivalents, beginning of period			74,488	331,224
Cash and cash equivalents, end of period	141,655	333,886	141,655	333,886
Parent [Member]
Cash flows from operating activities:
Net income (loss)	(152,906)	4,444	(480,294)	30,387
Adjustments to reconcile net income (loss) to net cash provided by operating activities:
Depreciation, depletion and amortization	44,052	30,385	86,164	58,440
Write-down of oil and gas properties	179,125		670,537
Accretion expense	91	61	182	129
Deferred income tax (benefit) provision	(77,863)	(13,858)	(274,097)	(19,765)
Settlement of asset retirement obligations			(14)	(82)
Non-cash stock compensation expense			6,028	5,358
Non-cash interest expense			8,737	8,229
Change in current income taxes			7,206	(6)
Non-cash (income) expense from investment in subsidiaries			(45,174)	(67,292)
Change in intercompany receivables/payables			15,070	(126,526)
(Increase) decrease in accounts receivable			16,968	(42,216)
Increase in other current assets			(1,895)	(82)
(Increase) decrease in inventory			(2,415)
Increase (decrease) in accounts payable			(500)	2,052
Increase (decrease) in other current liabilities			(8,409)	48,987
Other			(71)	381
Net cash (used in) provided by operating activities			(1,977)	(102,006)
Cash flows from investing activities:
Investment in oil and gas properties			(128,333)	(121,836)
Proceeds from sale of oil and gas properties, net of expenses				9,777
Investment in fixed and other assets			(727)	(3,896)
Change in restricted funds			177,647
Net cash provided by (used in) investing activities			48,587	(115,955)
Cash flows from financing activities:
Proceeds from bank borrowings			5,000
Net proceeds from issuance of common stock				226,036
Repayments of bank borrowings			(5,000)
Deferred financing costs				(3,167)
Net payments for share-based compensation			(3,069)	(6,948)
Net cash provided by (used in) financing activities			(3,069)	215,921
Net change in cash and cash equivalents			43,541	(2,040)
Cash and cash equivalents, beginning of period			72,886	246,294
Cash and cash equivalents, end of period	116,427	244,254	116,427	244,254
Guarantor Subsidiaries [Member]
Cash flows from operating activities:
Net income (loss)	45,065	29,939	74,092	67,280
Adjustments to reconcile net income (loss) to net cash provided by operating activities:
Depreciation, depletion and amortization	33,899	62,450	78,209	117,041
Accretion expense	6,317	7,672	12,635	15,159
Deferred income tax (benefit) provision	9,082	16,850	25,410	37,859
Settlement of asset retirement obligations			(35,909)	(24,833)
Non-cash derivative expense			7,931	2,697
Change in intercompany receivables/payables			(24,802)	114,841
(Increase) decrease in accounts receivable			6,079	16,692
(Increase) decrease in inventory			2,415
Increase (decrease) in accounts payable			(7,326)	(209)
Increase (decrease) in other current liabilities			(311)	1,798
Other			(433)	(1,056)
Net cash (used in) provided by operating activities			137,990	347,269
Cash flows from investing activities:
Investment in oil and gas properties			(124,506)	(384,349)
Proceeds from sale of oil and gas properties, net of expenses			10,100	42,178
Net cash provided by (used in) investing activities			(114,406)	(342,171)
Cash flows from financing activities:
Net change in cash and cash equivalents			23,584	5,098
Cash and cash equivalents, beginning of period			1,450	84,290
Cash and cash equivalents, end of period	25,034	89,388	25,034	89,388
Non-Guarantor Subsidiaries [Member]
Cash flows from operating activities:
Net income (loss)	(57,836)	16	(57,836)	24
Adjustments to reconcile net income (loss) to net cash provided by operating activities:
Write-down of oil and gas properties	45,169		45,169
Deferred income tax (benefit) provision	(16,267)		(16,267)
Non-cash (income) expense from investment in subsidiaries			28,918	(12)
Change in intercompany receivables/payables			9,732	11,685
Increase in other current assets			(64)
Net cash (used in) provided by operating activities			9,652	11,697
Cash flows from investing activities:
Investment in oil and gas properties			(11,516)	(11,719)
Change in restricted funds			1,828	(356)
Investment in subsidiaries			(9,684)	(12,176)
Net cash provided by (used in) investing activities			(19,372)	(24,251)
Cash flows from financing activities:
Equity proceeds from parent			9,684	12,176
Net cash provided by (used in) financing activities			9,684	12,176
Effect of exchange rate changes on cash			78	(18)
Net change in cash and cash equivalents			42	(396)
Cash and cash equivalents, beginning of period			152	640
Cash and cash equivalents, end of period	194	244	194	244
Eliminations [Member]
Cash flows from operating activities:
Net income (loss)	$ 12,771	$ (29,955)	(16,256)	(67,304)
Adjustments to reconcile net income (loss) to net cash provided by operating activities:
Non-cash (income) expense from investment in subsidiaries			16,256	67,304
Cash flows from investing activities:
Investment in subsidiaries			9,684	12,176
Net cash provided by (used in) investing activities			9,684	12,176
Cash flows from financing activities:
Equity proceeds from parent			(9,684)	(12,176)
Net cash provided by (used in) financing activities			$ (9,684)	$ (12,176)