Number of Well Locations

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Percentage of Developed Portion of Proved Reserves

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Percentage of Undeveloped Portion of Proved Reserves

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- Definition

Proved Developed And Undeveloped Reserves, Purchases Of Minerals In Place, Equivalent

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- Definition

Proved Developed And Undeveloped Reserves, Revisions Of Previous Estimates, Increase Decrease, Equivalent

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- Definition

Proved Developed And Undeveloped Reserves, Sales Of Minerals In Place, Equivalent

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- Definition

Proved Developed and Undeveloped Reserves, Pay-Add Locations

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- Definition

Proved Developed and Undeveloped Reserves, Reserves Included in Engineer Estimates of Proved Reserves, Percent

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- Definition

Proved Development And Undeveloped Reserves, Extensions, Discoveries, And Additions, Equivalent

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Oil and Natural Gas Operations (Unaudited) (Oil and Gas Operations, Activities) (Details)	12 Months Ended
	Dec. 31, 2015 MMBoe	Dec. 31, 2014 MMBoe well_location pay_add	Dec. 31, 2013 MMBoe well_location pay_add
Reserve Quantities [Line Items]
Reserves included in engineer estimates, percent	99.00%
Revisions of previous estimates	(58.9)	(75.7)	4.6
Purchases	0.0	0.1	0.2
Extensions and discoveries	132.6	130.0	36.8
Percentage of undeveloped portion of proved reserves	78.00%	70.00%	45.00%
Percentage of developed portion of proved reserves	22.00%	30.00%	55.00%
Sales	67.7	3.7	14.8
Extension Drilling
Reserve Quantities [Line Items]
Extensions and discoveries	3.1	89.6	21.6
Exploratory Drilling
Reserve Quantities [Line Items]
Extensions and discoveries	129.5	40.4	15.2
Price Related Revisions
Reserve Quantities [Line Items]
Revisions of previous estimates	(38.0)	3.9	7
Expected to Be Drilled Beyond Five Years
Reserve Quantities [Line Items]
Revisions of previous estimates	(8.2)
No Longer Expected to be Drilled
Reserve Quantities [Line Items]
Revisions of previous estimates			(5.3)
No Longer Expected to Be Drilled Beyond Five Years
Reserve Quantities [Line Items]
Revisions of previous estimates		(53.4)	(4.6)
San Juan Basin properties
Reserve Quantities [Line Items]
Revisions of previous estimates		1.6	2.2
Extensions and discoveries		1.1	2.3
Number of well locations \| well_location		16
Pay-add locations \| pay_add		10	30
San Juan Basin properties \| Price Related Revisions
Reserve Quantities [Line Items]
Revisions of previous estimates		4.4	5.9
San Juan Basin properties \| Higher Operating Costs
Reserve Quantities [Line Items]
Revisions of previous estimates		(1.5)
San Juan Basin properties \| Expected to Be Drilled Beyond Five Years
Reserve Quantities [Line Items]
Revisions of previous estimates			(4.6)
Permian Basin unproved leasehold properties
Reserve Quantities [Line Items]
Revisions of previous estimates	(5.5)	(77.3)	1.2
Extensions and discoveries		128.6	34.4
Number of well locations \| well_location		361	262
Permian Basin unproved leasehold properties \| Price Related Revisions
Reserve Quantities [Line Items]
Revisions of previous estimates			0.4
Permian Basin unproved leasehold properties \| Higher Operating Costs
Reserve Quantities [Line Items]
Revisions of previous estimates		(5.4)
Permian Basin unproved leasehold properties \| Interference Caused by Welbore Placement Geometry [Member]
Reserve Quantities [Line Items]
Revisions of previous estimates	(5.0)
Permian Basin unproved leasehold properties \| Reclassifying as Unproved
Reserve Quantities [Line Items]
Revisions of previous estimates		(53.4)
Permian Basin unproved leasehold properties \| Well Performance Revisions
Reserve Quantities [Line Items]
Revisions of previous estimates		(13.3)
Permian Basin unproved leasehold properties \| No Longer Expected to be Drilled
Reserve Quantities [Line Items]
Revisions of previous estimates			(0.7)
Permian Basin unproved leasehold properties \| Change in Year-End Pricing Revisions
Reserve Quantities [Line Items]
Revisions of previous estimates		(0.5)
North Louisiana/East Texas oil and natural gas properties
Reserve Quantities [Line Items]
Sales		3.7
Black Warrior Basin
Reserve Quantities [Line Items]
Sales			14.8