Selected Quarterly Financial Data (Unaudited) - Selected Quarterly Financial Data (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Revenues and other income:
Revenues and other income									$ 2,600,934	$ 3,333,837
Derivative fair value (loss) income	$ 18,491	$ 74,676	$ 195,245	$ (61,731)	$ 100,698	$ (34,591)	$ (103,290)	$ (14,009)	226,681	(51,192)	$ 213,350
Total revenues and other income	605,604	622,445	851,429	748,137	1,072,637	811,225	656,184	742,599	2,827,615	3,282,645	2,611,030
Costs and expenses:
Production and ad valorem taxes	8,963	7,805	9,889	11,310	16,656	9,427	10,140	9,926	37,967	46,149	42,882
Brokered natural gas and marketing	46,532	79,938	101,117	132,305	221,626	116,080	102,747	55,594	359,892	496,047	220,311
Exploration	9,350	11,013	8,109	8,211	10,600	8,299	7,499	7,719	36,683	34,117	53,662
Abandonment and impairment of unproved properties	1,193,711	16,202	12,770	12,659	441,750	6,549	54,922	11,773	1,235,342	514,994	269,725
General and administrative	42,793	41,047	50,631	46,638	50,090	43,722	47,583	68,417	181,109	209,812	233,406
Termination costs	6,481	819	2,206	0	0	(336)	0	(37)	9,506	(373)	3,770
Deferred compensation plan	960	(8,871)	(11,142)	3,581	(18,072)	223	6,615	(7,397)	(15,472)	(18,631)	(50,915)
Interest	44,024	46,997	51,727	51,537	49,161	54,801	53,862	52,385	194,285	210,209	195,679
Gain on early extinguishment of debt	(2,430)	(2,985)	0	0					(5,415)	0	0
Depletion, depreciation and amortization	130,869	137,751	141,505	138,718	147,909	164,266	161,026	162,266	548,843	635,467	624,992
Impairment of proved properties and other	1,095,634	0	0	0	0	0	15,302	7,312	1,095,634	22,614	63,679
Impairment of goodwill					1,641,197	0	0	0	0	1,641,197	0
Loss (gain) on sale of assets	(407)	36,341	(5,867)	189	10,815	30	(156)	(23)	30,256	10,666	(23,716)
Total costs and expenses	2,909,783	697,245	696,145	741,030	2,905,843	738,549	764,538	650,685	5,044,203	5,059,615	2,528,910
(Loss) income before income taxes	(2,304,179)	(74,800)	155,284	7,107	(1,833,206)	72,676	(108,354)	91,914	(2,216,588)	(1,776,970)	82,120
Income tax expense (benefit):
Current	2,068	4,079	0	0	0	0	0	0	6,147	0	17
Deferred	(500,927)	(51,298)	40,099	5,688	(68,784)	24,137	(28,518)	42,676	(506,438)	(30,489)	(251,043)
Total (benefit) expense for income taxes	(498,859)	(47,219)	40,099	5,688	(68,784)	24,137	(28,518)	42,676	(500,291)	(30,489)	(251,026)
Net (loss) income	$ (1,805,320)	$ (27,581)	$ 115,185	$ 1,419	$ (1,764,422)	$ 48,539	$ (79,836)	$ 49,238	$ (1,716,297)	$ (1,746,481)	$ 333,146
Net income (loss) per common share:
Basic	$ (7.27)	$ (0.11)	$ 0.46	$ 0.01	$ (7.15)	$ 0.19	$ (0.32)	$ 0.20	$ (6.92)	$ (7.10)	$ 1.34
Diluted	$ (7.27)	$ (0.11)	$ 0.46	$ 0.01	$ (7.15)	$ 0.19	$ (0.32)	$ 0.20	$ (6.92)	$ (7.10)	$ 1.34
Natural Gas, NGLs and Oil Sales
Revenues and other income:
Revenues and other income	$ 545,438	$ 474,754	$ 563,579	$ 671,654	$ 756,627	$ 736,431	$ 661,390	$ 696,629	$ 2,255,425	$ 2,851,077	$ 2,176,287
Brokered Natural Gas, Marketing and Other
Revenues and other income:
Revenues and other income	41,675	73,015	92,605	138,214	215,312	109,385	98,084	59,979	345,509	482,760	221,393
Direct Operating
Costs and expenses:
Costs and expenses	33,792	35,276	33,981	33,227	35,395	30,926	35,088	38,122	136,276	139,531	134,252
Transportation, Gathering, Processing and Compression
Costs and expenses:
Costs and expenses	$ 299,511	$ 295,912	$ 301,219	$ 302,655	$ 298,716	$ 304,562	$ 269,910	$ 244,628	$ 1,199,297	$ 1,117,816	$ 761,183