Selected Quarterly Financial Data (Unaudited) - Selected Quarterly Financial Data (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended									9 Months Ended	12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2014	Dec. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Revenues and other income:
Natural gas, NGLs and oil sales	$ 603,159	$ 507,541	$ 506,137	$ 559,450	$ 458,645	$ 304,477	$ 224,606	$ 209,487			$ 2,176,287	$ 1,197,215	$ 1,089,644
Derivative fair value income (loss)	25,024	(88,426)	111,195	165,557	(250,057)	64,556	(162,798)	86,908			213,350	(261,391)	416,364
Brokered natural gas, marketing and other	50,849	63,117	55,779	51,648	44,934	44,174	39,989	35,018			221,393	164,115	92,060
Total revenues and other income	679,032	482,232	673,111	776,655	253,522	413,207	101,797	331,413			2,611,030	1,099,939	1,598,068
Costs and expenses:
Direct operating	37,921	36,888	31,420	28,023	30,276	22,387	20,671	24,054			134,252	97,388	136,363
Transportation, gathering, processing and compression	200,300	191,645	191,590	177,648	164,338	138,764	136,844	125,263			761,183	565,209	396,739
Production and ad valorem taxes	11,757	11,993	9,969	9,163	6,790	6,717	6,049	5,887			42,882	25,443	33,860
Brokered natural gas and marketing	51,131	59,773	55,857	53,550	46,471	44,622	40,925	36,558			220,311	168,576	115,866
Exploration	7,893	22,767	14,498	8,504	13,684	6,943	6,785	4,913			53,662	32,325	21,406
Abandonment and impairment of unproved properties	217,544	42,568	5,193	4,420	6,307	6,082	7,059	10,628			269,725	30,076	47,619
General and administrative	80,553	53,035	52,322	47,496	57,027	41,024	46,064	40,657			233,406	184,772	194,015
MRD Merger expenses					813	33,791	2,621	0		$ 37,200	0	37,225	0
Termination costs	(279)	(47)	(96)	4,192	(822)	136	5	162	$ 8,400		3,770	(519)	15,070
Deferred compensation plan	(14,077)	(9,203)	(14,466)	(13,169)	(11,013)	(11,636)	25,746	16,056			(50,915)	19,153	(77,627)
Interest	51,473	49,179	47,926	47,101	46,749	45,967	37,758	37,739			195,679	168,213	166,439
Loss on early extinguishment of debt											0	0	22,495
Depletion, depreciation and amortization	162,918	159,749	152,504	149,821	149,662	131,489	122,390	120,561			624,992	524,102	581,155
Impairment of proved properties and other	0	63,679	0	0	0	0	0	43,040			63,679	43,040	590,174
(Gain) loss on the sale of assets	(207)	(102)	(807)	(22,600)	(470)	2,597	3,304	1,643			(23,716)	7,074	406,856
Total costs and expenses	806,927	681,924	545,910	494,149	509,812	468,883	456,221	467,161			2,528,910	1,902,077	2,650,430
Income (loss) before income taxes	(127,895)	(199,692)	127,201	282,506	(256,290)	(55,676)	(354,424)	(135,748)			82,120	(802,138)	(1,052,362)
Income tax (benefit) expense:
Current	17	0	0	0	98	0	0	0			17	98	29
Deferred	(349,097)	(71,992)	57,651	112,395	(95,679)	(13,705)	(129,488)	(41,976)			(251,043)	(280,848)	(338,706)
Total (benefit) expense for income taxes	(349,080)	(71,992)	57,651	112,395	(95,581)	(13,705)	(129,488)	(41,976)			(251,026)	(280,750)	(338,677)
Net income (loss)	$ 221,185	$ (127,700)	$ 69,550	$ 170,111	$ (160,709)	$ (41,971)	$ (224,936)	$ (93,772)			$ 333,146	$ (521,388)	$ (713,685)
Net income (loss) per common share:
Basic	$ 0.89	$ (0.52)	$ 0.28	$ 0.69	$ (0.66)	$ (0.23)	$ (1.35)	$ (0.56)			$ 1.34	$ (2.75)	$ (4.29)
Diluted	$ 0.89	$ (0.52)	$ 0.28	$ 0.69	$ (0.66)	$ (0.23)	$ (1.35)	$ (0.56)			$ 1.34	$ (2.75)	$ (4.29)