Annual report pursuant to Section 13 and 15(d)

Supplemental Oil and Gas Disclosures - Estimated Quantities of Net Proved, Proved Developed and Proved Undeveloped Oil, Ngls and Natural Gas Reserves (Parenthetical) (Details)

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Supplemental Oil and Gas Disclosures - Estimated Quantities of Net Proved, Proved Developed and Proved Undeveloped Oil, Ngls and Natural Gas Reserves (Parenthetical) (Details) - MMBoe
 1 Months Ended 12 Months Ended
Oct. 31, 2015
Dec. 31, 2015
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Reserve Quantities [Line Items]          
Proved undeveloped reserves, that will not be developed with in five years   1.2      
Percentage of proved undeveloped reserves that will be developed with in five years   16.00%      
Wells expected to be drilled, year     2020    
Barrel Equivalent          
Reserve Quantities [Line Items]          
Revisions of previous estimates [2]   4.7 [1] 4.1 [3] (3.8) [4]  
Extensions and discoveries [2]   4.1 [5] 9.7 [6] 20.2 [7]  
Proved reserves [2]   76.4 120.0 117.7 117.5
Barrel Equivalent | Proved Undeveloped Reserves          
Reserve Quantities [Line Items]          
Proved reserves [2]   7.4 [8] 36.7 31.6  
Changes due to price          
Reserve Quantities [Line Items]          
Revisions of previous estimates   10.7 0.3 1.9  
Changes at the Yellow Rose field          
Reserve Quantities [Line Items]          
Revisions of previous estimates     (3.9) 4.9  
Extensions and discoveries     4.1 12.6  
Proved estimated reserve at the date of sale 19.0        
Changes at the High Island 21/22 field          
Reserve Quantities [Line Items]          
Revisions of previous estimates       2.3  
Changes at the Ship Shoal 349/359 field          
Reserve Quantities [Line Items]          
Revisions of previous estimates       1.3  
Changes at the Main Pass 98 field          
Reserve Quantities [Line Items]          
Revisions of previous estimates       0.7  
Changes at the South Timbalier 314 field          
Reserve Quantities [Line Items]          
Revisions of previous estimates       0.7  
Changes at the Main Pass 108 field          
Reserve Quantities [Line Items]          
Revisions of previous estimates       0.6  
Changes at the South Timbalier 176 field          
Reserve Quantities [Line Items]          
Revisions of previous estimates       0.5  
Changes at the Ship Shoal 349 field          
Reserve Quantities [Line Items]          
Extensions and discoveries       4.2  
Changes at the Mississippi Canyon 698 field          
Reserve Quantities [Line Items]          
Extensions and discoveries       1.9  
Changes at the Fairway Field          
Reserve Quantities [Line Items]          
Revisions of previous estimates   1.1 2.4    
Changes at the Mississippi Canyon 800 field          
Reserve Quantities [Line Items]          
Revisions of previous estimates     1.2    
Various field positive revisions          
Reserve Quantities [Line Items]          
Revisions of previous estimates     6.4    
Various field negative revisions          
Reserve Quantities [Line Items]          
Revisions of previous estimates     (2.4)    
Changes at the Mississippi Canyon 782 field          
Reserve Quantities [Line Items]          
Extensions and discoveries     4.1    
Changes at Ship Shoal 349 Field (Mahogany)          
Reserve Quantities [Line Items]          
Revisions of previous estimates   7.4      
Changes at the Brazo A-133 Field          
Reserve Quantities [Line Items]          
Revisions of previous estimates   1.9      
Changes at Atwater 575 Field          
Reserve Quantities [Line Items]          
Revisions of previous estimates   1.3      
Mississippi Canyon 243 Field (Matterhorn)          
Reserve Quantities [Line Items]          
Revisions of previous estimates   1.3      
[1] Includes upwards revisions of 7.4 MMBoe at the Ship Shoal 349 field (Mahogany), 1.9 MMBoe at our Brazo A-133 field, 1.3 MMBoe at out Atwater 575 field, 1.3 MMBoe at out Mississippi Canyon 243 field (Matterhorn), 1.1 MMBoe at our Fairway Field, partially offset by downward revisions due to price of 10.7 MMBoe. The revision for price excludes the Yellow Rose field sold during 2015.
[2] The conversion to barrels of oil equivalent and cubic feet equivalent were determined using the energy-equivalent ratio of six Mcf of natural gas to one barrel of crude oil, condensate or NGLs (totals may not compute due to rounding). The energy-equivalent ratio does not assume price equivalency, and the energy-equivalent prices for crude oil, NGLs and natural gas may differ significantly.
[3] Includes upwards revisions due to price of 0.3 MMBoe; positive revisions of 2.4 MMBoe at our Fairway Field, 1.2 MMBoe at our Mississippi Canyon 800 field and 6.4 MMBoe at various fields; and negative revisions of 3.9 MMBoe at our Yellow Rose field and 2.4 MMBoe at various other fields.
[4] Includes upward revision due to price of 1.9 MMBoe; negative revisions of 4.9 MMBoe at our Yellow Rose field for performance and technical changes, 2.3 MMBoe at our High Island 21/22 field for performance, 1.3 MMBoe at our Ship Shoal 349/359 field for performance; and positive performance revisions of 0.7 MMBoe at our Main Pass 98 field, 0.7 MMBoe at our South Timbalier 314, 0.6 MMBoe at our Main Pass 108 field and 0.5 MMBoe our South Timbalier 176 field.
[5] Primarily due to increases at Ewing Bank 910.
[6] Includes extensions and discoveries of 4.1 MMBoe at our Yellow Rose field and 4.1 MMBoe at our Mississippi Canyon 782 field.
[7] Includes extensions and discoveries of 12.6 MMBoe at our Yellow Rose field, 4.2 MMBoe at our Ship Shoal 349 field and 1.9 MMBoe at our Mississippi Canyon 698 field.
[8] We believe that we will be able to develop all but 1.2 MMBoe of the reserves classified as proved undeveloped (“PUDs”), or approximately 16%, out of the total of 7.4 MMBoe classified as PUDs at December 31, 2015, within five years from the date such reserves were initially recorded. The exception is at the Mississippi Canyon 243 field (Matterhorn) where the field is being developed using a single floating tension leg platform requiring an extended sequential development plan. The platform cannot support a rig that would allow additional wells to be drilled, but can support a rig to allow sidetracking of wells. A portion of the PUDs in this field were originally recorded in our reserves as of December 31, 2010. The development of these PUDs will be delayed until an existing well is depleted and available to sidetrack. Based on the latest reserve report, a well is expected to be drilled to develop the Mississippi Canyon 243 field (Matterhorn) PUDs in 2020.