Selected Quarterly Financial Data (Unaudited) - Selected Quarterly Financial Data (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended									12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Revenues and other income:
Natural gas, NGLs and oil sales	$ 458,645	$ 304,477	$ 224,606	$ 209,487	$ 254,043	$ 252,065	$ 258,053	$ 325,483		$ 1,197,215	$ 1,089,644	$ 1,911,989
Derivative fair value income (loss)	(250,057)	64,556	(162,798)	86,908	126,312	202,004	(34,791)	122,839		(261,391)	416,364	383,520
Brokered natural gas, marketing and other	44,934	44,174	39,989	35,018	30,372	25,864	21,339	14,485		164,115	92,060	130,548
Total revenues and other income	253,522	413,207	101,797	331,413	410,727	479,933	244,601	462,807		1,099,939	1,598,068	2,426,057
Costs and expenses:
Direct operating	30,276	22,387	20,671	24,054	29,388	35,058	34,780	37,137		97,388	136,363	150,483
Transportation, gathering and compression	164,338	138,764	136,844	125,263	112,481	99,634	95,198	89,426		565,209	396,739	325,289
Production and ad valorem taxes	6,790	6,717	6,049	5,887	7,354	7,336	9,242	9,928		25,443	33,860	44,555
Brokered natural gas and marketing	46,471	44,622	40,925	36,558	34,942	32,331	27,031	21,562		168,576	115,866	129,980
Exploration	13,684	6,943	6,785	4,913	4,260	4,235	5,025	7,886		32,325	21,406	63,548
Abandonment and impairment of unproved properties	6,307	6,082	7,059	10,628	11,432	12,366	12,330	11,491		30,076	47,619	47,079
General and administrative	57,027	41,024	46,064	40,657	43,544	46,178	55,964	48,329		184,772	194,015	213,426
MRD Merger expenses	813	33,791	2,621	0						37,225	0	0
Termination costs	(822)	136	5	162	8,780	(77)	417	5,950	$ 8,400	(519)	15,070	8,371
Deferred compensation plan	(11,013)	(11,636)	25,746	16,056	(21,016)	(43,705)	(7,282)	(5,624)		19,153	(77,627)	(74,550)
Interest	46,749	45,967	37,758	37,739	40,849	42,904	43,479	39,207		168,213	166,439	168,977
Loss on early extinguishment of debt	0	0	0	0	0	22,495	0	0		0	22,495	24,596
Depletion, depreciation and amortization	149,662	131,489	122,390	120,561	127,977	153,993	151,895	147,290		524,102	581,155	551,032
Impairment of proved properties and other	0	0	0	43,040	87,941	502,233	0	0		43,040	590,174	28,024
Loss (gain) on the sale of assets	(470)	2,597	3,304	1,643	408,909	681	(2,909)	175		7,074	406,856	(285,638)
Total costs and expenses	509,812	468,883	456,221	467,161	896,841	915,662	425,170	412,757		1,902,077	2,650,430	1,395,172
(Loss) income before income taxes	(256,290)	(55,676)	(354,424)	(135,748)	(486,114)	(435,729)	(180,569)	50,050		(802,138)	(1,052,362)	1,030,885
Income tax (benefit) expense:
Current	98	0	0	0	29	0	0	0		98	29	1
Deferred	(95,679)	(13,705)	(129,488)	(41,976)	(164,316)	(134,781)	(61,975)	22,366		(280,848)	(338,706)	396,502
Total income tax (benefit) expense	(95,581)	(13,705)	(129,488)	(41,976)	(164,287)	(134,781)	(61,975)	22,366		(280,750)	(338,677)	396,503
Net (loss) income	$ (160,709)	$ (41,971)	$ (224,936)	$ (93,772)	$ (321,827)	$ (300,948)	$ (118,594)	$ 27,684		$ (521,388)	$ (713,685)	$ 634,382
Net (loss) income per common share:
Basic	$ (0.66)	$ (0.23)	$ (1.35)	$ (0.56)	$ (1.93)	$ (1.81)	$ (0.71)	$ 0.16		$ (2.75)	$ (4.29)	$ 3.81
Diluted	$ (0.66)	$ (0.23)	$ (1.35)	$ (0.56)	$ (1.93)	$ (1.81)	$ (0.71)	$ 0.16		$ (2.75)	$ (4.29)	$ 3.79