Supplemental Oil and Natural Gas Information - Proved Developed and Proved Undeveloped Reserves (Detail)	12 Months Ended
	Dec. 31, 2018 Bcfe Bcf MBbls	Dec. 31, 2017 Bcfe Bcf MBbls	Dec. 31, 2016 Bcfe Bcf MBbls	Dec. 31, 2015 Bcfe Bcf MBbls
Reserve Quantities [Line Items]
Proved Developed and Undeveloped Reserves (energy), beginning balance | Bcfe	1,458.6	469.4	348.8
Revisions (energy) | Bcfe	(42.8)	695.6	14.8
Extensions and discoveries (energy) | Bcfe	558.1	405.1	196.1
Acquisitions (energy) | Bcfe	16.3	1.9	4.1
Divestitures (energy) | Bcfe	(0.2)		(10.7)
Production (energy) | Bcfe	(125.3)	(113.4)	(83.7)
Proved Developed and Undeveloped Reserves (energy), ending balance | Bcfe	1,864.7	1,458.6	469.4
Proved developed reserves (energy) | Bcfe	670.7	456.0	297.8	278.4
Proved undeveloped reserves (energy) | Bcfe	1,194.1	1,002.6	171.6	70.3
Natural Gas [Member]
Reserve Quantities [Line Items]
Proved Developed and Undeveloped Reserves, beginning balance | Bcf	1,090.1	386.4	274.1
Revisions | Bcf	5.6	515.1	(0.1)
Extensions and discoveries | Bcf	515.8	274.4	175.4
Acquisitions | Bcf	9.9	1.6	3.8
Divestitures | Bcf	(0.2)		(5.9)
Production | Bcf	(90.0)	(87.4)	(60.9)
Proved Developed and Undeveloped Reserves, ending balance | Bcf	1,531.2	1,090.1	386.4
Proved developed reserves | Bcf	501.0	334.6	226.1	209.5
Proved undeveloped reserves | Bcf	1,030.2	755.5	160.4	64.5
Natural Gas Liquids [Member]
Reserve Quantities [Line Items]
Proved Developed and Undeveloped Reserves, beginning balance	41,930.6	8,675.5	7,758.7
Revisions	(8,307.5)	20,327.3	1,273.7
Extensions and discoveries	4,059.4	15,598.8	2,156.0
Acquisitions	551	42.6	24.8
Divestitures			(91.5)
Production	(3,503.0)	(2,713.6)	(2,446.2)
Proved Developed and Undeveloped Reserves, ending balance	34,730.9	41,930.6	8,675.5
Proved developed reserves	20,213.8	13,782.9	7,520.0	7,245.7
Proved undeveloped reserves	14,517.2	28,147.7	1,155.5	513.0
Oil [Member]
Reserve Quantities [Line Items]
Proved Developed and Undeveloped Reserves, beginning balance	19,480.8	5,157.7	4,693.1
Revisions	231.2	9,746.8	1,196.8
Extensions and discoveries	2,995.7	6,192.9	1,300.2
Acquisitions	522	5.8	15.1
Divestitures			(703.7)
Production	(2,377.8)	(1,622.4)	(1,343.8)
Proved Developed and Undeveloped Reserves, ending balance	20,852.1	19,480.8	5,157.7
Proved developed reserves	8,058.7	6,449.6	4,439.5	4,239.2
Proved undeveloped reserves	12,793.4	13,031.2	718.1	453.9