Supplemental Information on Natural Gas and Oil Exploration, Development and Production Activities (Unaudited) - Proved Developed and Undeveloped Reserves (Detail)		12 Months Ended
		Dec. 31, 2018 MMcfe MMcf MBbls	Dec. 31, 2017 MMcfe MMcf MBbls	Dec. 31, 2016 MMcfe MMcf MBbls
Proved undeveloped reserves:
Proved undeveloped reserves | MMcfe		8,315,535	6,914,287
Natural Gas
Reserve Quantities [Line Items]
Beginning Balance | MMcf		10,263,649	7,870,416	6,277,697
Revisions | MMcf		178,595	70,222	(7,441)
Extensions, discoveries and additions | MMcf		2,269,427	2,866,103	1,193,154
Purchases | MMcf			7,738	943,544
Property sales | MMcf		(135,884)	(60,278)	(160,727)
Production | MMcf		(548,085)	(490,552)	(375,811)
Ending Balance | MMcf		12,027,702	10,263,649	7,870,416
Proved developed reserves:
Proved developed reserves | MMcf		6,451,012	5,437,674	4,352,141
Proved undeveloped reserves:
Proved undeveloped reserves | MMcf		5,576,690	4,825,975	3,518,275
NGLs
Reserve Quantities [Line Items]
Beginning Balance		763,264	630,066	549,135
Revisions		84,993	83,338	41,402
Extensions, discoveries and additions		128,436	87,572	26,991
Purchases			330	40,724
Property sales		(16,774)	(2,356)	(360)
Production		(38,325)	(35,686)	(27,826)
Ending Balance		921,594	763,264	630,066
Proved developed reserves:
Proved developed reserves		512,318	448,258	363,852
Proved undeveloped reserves:
Proved undeveloped reserves		409,276	315,006	266,214
Crude Oil and Condensate
Reserve Quantities [Line Items]
Beginning Balance		69,854	70,252	53,193
Revisions		7,197	(10,555)	2,471
Extensions, discoveries and additions		17,309	15,997	6,506
Purchases			66	11,986
Property sales		(4,276)	(1,121)	(295)
Production		(4,228)	(4,785)	(3,609)
Ending Balance		85,856	69,854	70,252
Proved developed reserves:
Proved developed reserves		38,658	36,808	39,110
Proved undeveloped reserves:
Proved undeveloped reserves		47,198	33,046	31,143
Natural Gas Equivalents
Proved developed reserves:
Proved developed reserves | MMcfe	[1]	9,756,870	8,348,074	6,769,908
Proved undeveloped reserves:
Proved undeveloped reserves | MMcfe	[1]	8,315,536	6,914,287	5,302,414
Beginning Balance | MMcfe	[1]	15,262,361	12,072,322	9,891,663
Revisions | MMcfe	[1]	731,735	506,919	255,794
Extensions, discoveries and additions | MMcfe	[1]	3,143,898	3,487,519	1,394,134
Purchases | MMcfe	[1]		10,116	1,259,806
Property sales | MMcfe	[1]	(262,180)	(81,133)	(164,655)
Production | MMcfe	[1]	(803,408)	(733,382)	(564,420)
Ending Balance | MMcfe	[1]	18,072,406	15,262,361	12,072,322

[1] Oil and NGLs are converted to mcfe at the rate of one barrel equals six mcf based upon the approximate relative energy content of oil to natural gas, which is not indicative of the relationship between oil and natural gas prices.