Guarantor Financial Statements - Condensed Consolidating Statement of Cash Flows (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Cash flows from operating activities:
Net income (loss)	$ (291,965)	$ (29,415)	$ (772,259)	$ 972
Adjustments to reconcile net income (loss) to net cash provided by operating activities:
Depreciation, depletion and amortization	61,936	80,291	226,309	255,772
Write-down of oil and gas properties	295,679	47,130	1,011,385	47,130
Accretion expense	6,498	6,539	19,315	21,827
Deferred income tax (benefit) provision	(15,806)	(14,495)	(280,760)	3,599
Settlement of asset retirement obligations			(59,826)	(47,217)
Non-cash stock compensation expense			9,163	8,409
Non-cash derivative (income) expense			10,854	(2,386)
Non-cash interest expense			13,210	12,393
Change in current income taxes			7,211	(6)
(Increase) decrease in accounts receivable			33,895	(1,805)
Increase in other current assets			(1,090)	(10)
Decrease in accounts payable			(11,592)	(3,547)
Increase (decrease) in other current liabilities			(6,753)	37,441
Other			(82)	(172)
Net cash provided by operating activities			198,980	332,400
Cash flows from investing activities:
Investment in oil and gas properties			(385,528)	(727,488)
Proceeds from sale of oil and gas properties, net of expenses			11,643	223,299
Investment in fixed and other assets			(1,455)	(8,790)
Change in restricted funds			179,475	(185,752)
Net cash used in investing activities			(195,865)	(698,731)
Cash flows from financing activities:
Proceeds from bank borrowings			5,000	0
Net proceeds from issuance of common stock			0	225,999
Repayments of bank borrowings			(5,000)	0
Deferred financing costs			0	(3,329)
Net payments for share-based compensation			(3,127)	(7,161)
Net cash provided by (used in) financing activities			(3,127)	215,509
Effect of exchange rate changes on cash			(2)	(95)
Net change in cash and cash equivalents			(14)	(150,917)
Cash and cash equivalents, beginning of period			74,488	331,224
Cash and cash equivalents, end of period	74,474	180,307	74,474	180,307
Parent [Member]
Cash flows from operating activities:
Net income (loss)	(291,965)	(29,415)	(772,259)	972
Adjustments to reconcile net income (loss) to net cash provided by operating activities:
Depreciation, depletion and amortization	27,518	36,598	113,682	95,038
Write-down of oil and gas properties	295,679	47,130	966,216	47,130
Accretion expense	92	56	274	185
Deferred income tax (benefit) provision	160,986	(31,309)	(113,111)	(51,074)
Settlement of asset retirement obligations			(15)	(84)
Non-cash stock compensation expense			9,163	8,409
Non-cash interest expense			13,210	12,393
Change in current income taxes			7,211	(6)
Non-cash (income) expense from investment in subsidiaries			(273,147)	(97,185)
Change in intercompany receivables/payables			31,320	(119,004)
(Increase) decrease in accounts receivable			29,561	125,593
Increase in other current assets			(1,050)	(2)
(Increase) decrease in inventory			(2,415)
Decrease in accounts payable			(7,562)	900
Increase (decrease) in other current liabilities			(6,855)	39,329
Other			645	1,414
Net cash provided by operating activities			(5,132)	64,008
Cash flows from investing activities:
Investment in oil and gas properties			(177,497)	(225,831)
Proceeds from sale of oil and gas properties, net of expenses				12,197
Investment in fixed and other assets			(1,455)	(8,790)
Change in restricted funds			177,647	(177,647)
Net cash used in investing activities			(1,305)	(400,071)
Cash flows from financing activities:
Proceeds from bank borrowings			5,000
Net proceeds from issuance of common stock				225,999
Repayments of bank borrowings			(5,000)
Deferred financing costs				(3,329)
Net payments for share-based compensation			(3,127)	(7,161)
Net cash provided by (used in) financing activities			(3,127)	215,509
Net change in cash and cash equivalents			(9,564)	(120,554)
Cash and cash equivalents, beginning of period			72,886	246,294
Cash and cash equivalents, end of period	63,322	125,740	63,322	125,740
Guarantor Subsidiaries [Member]
Cash flows from operating activities:
Net income (loss)	244,245	29,895	318,337	97,175
Adjustments to reconcile net income (loss) to net cash provided by operating activities:
Depreciation, depletion and amortization	34,418	43,693	112,627	160,734
Write-down of oil and gas properties		0		0
Accretion expense	6,406	6,483	19,041	21,642
Deferred income tax (benefit) provision	(193,059)	16,814	(167,649)	54,673
Settlement of asset retirement obligations			(59,811)	(47,133)
Non-cash derivative (income) expense			10,854	(2,386)
Change in intercompany receivables/payables			(41,056)	90,313
(Increase) decrease in accounts receivable			4,317	(127,363)
(Increase) decrease in inventory			2,415
Decrease in accounts payable			(4,030)	(4,447)
Increase (decrease) in other current liabilities			102	(1,888)
Other			(727)	(1,586)
Net cash provided by operating activities			194,420	239,734
Cash flows from investing activities:
Investment in oil and gas properties			(197,471)	(480,686)
Proceeds from sale of oil and gas properties, net of expenses			11,643	211,102
Net cash used in investing activities			(185,828)	(269,584)
Cash flows from financing activities:
Net change in cash and cash equivalents			8,592	(29,850)
Cash and cash equivalents, beginning of period			1,450	84,290
Cash and cash equivalents, end of period	10,042	54,440	10,042	54,440
Non-Guarantor Subsidiaries [Member]
Cash flows from operating activities:
Net income (loss)	(32,544)	(3)	(90,380)	21
Adjustments to reconcile net income (loss) to net cash provided by operating activities:
Write-down of oil and gas properties	0		45,169
Deferred income tax (benefit) provision	16,267		0
Non-cash (income) expense from investment in subsidiaries			45,190	(11)
Change in intercompany receivables/payables			9,736	28,691
(Increase) decrease in accounts receivable			17	(35)
Increase in other current assets			(40)	(8)
Net cash provided by operating activities			9,692	28,658
Cash flows from investing activities:
Investment in oil and gas properties			(10,560)	(20,971)
Change in restricted funds			1,828	(8,105)
Investment in subsidiaries			(9,708)	(29,253)
Net cash used in investing activities			(18,440)	(58,329)
Cash flows from financing activities:
Equity proceeds from parent			9,708	29,253
Net cash provided by (used in) financing activities			9,708	29,253
Effect of exchange rate changes on cash			(2)	(95)
Net change in cash and cash equivalents			958	(513)
Cash and cash equivalents, beginning of period			152	640
Cash and cash equivalents, end of period	1,110	127	1,110	127
Eliminations [Member]
Cash flows from operating activities:
Net income (loss)	(211,701)	$ (29,892)	(227,957)	(97,196)
Adjustments to reconcile net income (loss) to net cash provided by operating activities:
Non-cash (income) expense from investment in subsidiaries			227,957	97,196
Cash flows from investing activities:
Investment in subsidiaries			9,708	29,253
Net cash used in investing activities			9,708	29,253
Cash flows from financing activities:
Equity proceeds from parent			(9,708)	(29,253)
Net cash provided by (used in) financing activities			(9,708)	$ (29,253)
Cash and cash equivalents, end of period	$ 0		$ 0