Supplemental Oil and Gas Disclosures - Proved Reserves (Detail)	12 Months Ended
	Dec. 31, 2019 MMBoe MMBbls MMcf	Dec. 31, 2018 MMBoe MMBbls MMcf	Dec. 31, 2017 MMBoe MMcf MMBbls	Dec. 31, 2016 MMBoe MMBbls MMcf
Reserve Quantities [Line Items]
Computation Of Oil Natural Gas And Ngl Reserves	Natural gas reserves are computed at 14.73 pounds per square inch absolute and 60 degrees Fahrenheit.
Oil [Member]
Reserve Quantities [Line Items]
Proved Developed and Undeveloped Reserves, Revisions of Previous Estimates	(10.7)	0	4.7
Proved Developed and Undeveloped Reserves, Net	295.8	291.3	263.7	174.6
Proved Developed and Undeveloped Reserves, Sales of Minerals in Place	(3.7)	(27.6)	(1.7)
Proved Developed and Undeveloped Reserves, Extensions, Discoveries, and Additions	56.7	84.5	86.7
Proved Developed and Undeveloped Reserves, Production	(37.8)	(30.8)	(22.4)
Proved Developed and Undeveloped Reserves, Purchases of Minerals in Place		1.5	21.8
Proved Undeveloped Reserve (Volume)	111.5	134.9	133.4
Proved Developed Reserves (Volume)	184.3	156.4	130.3
Natural Gas
Reserve Quantities [Line Items]
Proved Developed and Undeveloped Reserves, Revisions of Previous Estimates | MMcf	41,400	(11,400)	(8,400)
Proved Developed and Undeveloped Reserves, Net | MMcf	740,700	617,700	591,000.0	734,500
Proved Developed and Undeveloped Reserves, Sales of Minerals in Place | MMcf	(10,700)	(79,800)	(312,500)
Proved Developed and Undeveloped Reserves, Extensions, Discoveries, and Additions | MMcf	170,700	176,900	194,500
Proved Developed and Undeveloped Reserves, Production | MMcf	(78,400)	(63,800)	(75,900)
Proved Developed and Undeveloped Reserves, Purchases of Minerals in Place | MMcf		4,800	58,800
Proved Undeveloped Reserve (Volume) | MMcf	284,200	252,300	269,800
Proved Developed Reserves (Volume) | MMcf	456,500	365,400	321,200
Natural Gas Liquids
Reserve Quantities [Line Items]
Proved Developed and Undeveloped Reserves, Revisions of Previous Estimates	8.6	5.3	(1.1)
Proved Developed and Undeveloped Reserves, Net	108.3	85.0	74.0	49.5
Proved Developed and Undeveloped Reserves, Sales of Minerals in Place	(0.8)	(10.4)	(0.8)
Proved Developed and Undeveloped Reserves, Extensions, Discoveries, and Additions	25.5	22.7	23.6
Proved Developed and Undeveloped Reserves, Production	(10.0)	(7.2)	(5.0)
Proved Developed and Undeveloped Reserves, Purchases of Minerals in Place		0.6	7.8
Proved Undeveloped Reserve (Volume)	42.8	36.6	35.2
Proved Developed Reserves (Volume)	65.5	48.4	38.8
All products
Reserve Quantities [Line Items]
Beginning Balance | MMBoe	527.6	479.3	436.2	346.4
Revisions | MMBoe	4.8	3.4	2.3
Purchases | MMBoe		2.9	39.4
Divestitures | MMBoe	(6.3)	(51.3)	(54.6)
Extensions and discoveries | MMBoe	110.7	136.7	142.7
Production | MMBoe	(60.9)	(48.6)	(40.0)
Proved Developed Reserves (Energy) | MMBoe	325.9	265.8	222.7
Proved Undeveloped Reserves (Energy) | MMBoe	201.7	213.5	213.5
Proved Developed Reserves [Member]
Reserve Quantities [Line Items]
Purchases | MMBoe			23.8
Extensions and discoveries | MMBoe	42	52	46
Proved Undeveloped Reserves [Member] [Member]
Reserve Quantities [Line Items]
Extensions and discoveries | MMBoe	68	85	97
San Juan [Member] | Proved Developed Reserves [Member]
Reserve Quantities [Line Items]
Divestitures | MMBoe		(40)	(28.7)
San Juan [Member] | Proved Undeveloped Reserves [Member] [Member]
Reserve Quantities [Line Items]
Divestitures | MMBoe		(11)	(16.6)
Negative [Member]
Reserve Quantities [Line Items]
Revisions | MMBoe	(16)	(5)	(22)
Positive [Member]
Reserve Quantities [Line Items]
Revisions | MMBoe	21	9	24