Supplemental Oil and Natural Gas Information - Proved Developed and Proved Undeveloped Reserves (Detail)	12 Months Ended
	Dec. 31, 2016 Bcfe Bcf MBbls	Dec. 31, 2015 Bcfe Bcf MBbls	Dec. 31, 2014 Bcfe Bcf MBbls
Reserve Quantities [Line Items]
Proved Developed and Undeveloped Reserves (energy), beginning balance | Bcfe	348.8	355.8	78.5
Revisions (energy) | Bcfe	14.8	(152.9)	(19.3)
Extensions and discoveries (energy) | Bcfe	196.1	221.7	323.1
Production (energy) | Bcfe	(83.7)	(75.9)	(26.5)
Proved Developed and Undeveloped Reserves (energy), ending balance | Bcfe	469.4	348.8	355.8
Acquisitions (energy) | Bcfe	4.1
Divestitures (energy) | Bcfe	(10.7)
Proved developed reserves (energy) | Bcfe	297.8	278.4	196.8
Proved undeveloped reserves (energy) | Bcfe	171.6	70.3	159.0
Natural Gas [Member]
Reserve Quantities [Line Items]
Proved Developed and Undeveloped Reserves, beginning balance | Bcf	274.1	256.3	52.3
Revisions | Bcf	(0.1)	(115.3)	(12.1)
Extensions and discoveries | Bcf	175.4	182.6	235.8
Acquisitions | Bcf	3.8
Divestitures | Bcf	(5.9)
Production | Bcf	(60.9)	(49.5)	(19.8)
Proved Developed and Undeveloped Reserves, ending balance | Bcf	386.4	274.1	256.3
Proved developed reserves | Bcf	226.1	209.5	133.0
Proved undeveloped reserves | Bcf	160.4	64.5	123.4
Natural Gas Liquids [Member]
Reserve Quantities [Line Items]
Proved Developed and Undeveloped Reserves, beginning balance	7,758.7	10,879.0	1,938.4
Revisions	1,273.7	(4,705.7)	(739.7)
Extensions and discoveries	2,156.0	4,035.7	10,216.3
Acquisitions	24.8
Divestitures	(91.5)
Production	(2,446.2)	(2,450.3)	(536.0)
Proved Developed and Undeveloped Reserves, ending balance	8,675.5	7,758.7	10,879.0
Proved developed reserves	7,520.0	7,245.7	6,758.6
Proved undeveloped reserves	1,155.5	513.0	4,120.4
Oil [Member]
Reserve Quantities [Line Items]
Proved Developed and Undeveloped Reserves, beginning balance	4,693.1	5,697.4	2,417.4
Revisions	1,196.8	(1,550.1)	(462.6)
Extensions and discoveries	1,300.2	2,496.3	4,337.5
Acquisitions	15.1
Divestitures	(703.7)
Production	(1,343.8)	(1,950.5)	(594.9)
Proved Developed and Undeveloped Reserves, ending balance	5,157.7	4,693.1	5,697.4
Proved developed reserves	4,439.5	4,239.2	3,880.9
Proved undeveloped reserves	718.1	453.9	1,816.4