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, 2017
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Reserve Quantities [Line Items]          
Revisions of previous estimates   6.2 14.2    
Proved undeveloped reserves, that will not be developed within five years   1.8      
Percentage of proved undeveloped reserves that will be developed within five years   15.00%      
Wells expected to be drilled, year   2023      
Barrel Equivalent          
Reserve Quantities [Line Items]          
Revisions of previous estimates [2]   9.6 [1] 13.0 [3] 4.7 [4]  
Extensions and discoveries [2]   5.2 [5]   4.1 [6]  
Proved reserves [2]   74.2 74.0 76.4 120.0
Barrel Equivalent | Proved Undeveloped Reserves          
Reserve Quantities [Line Items]          
Proved reserves [2]   12.0 [7] 9.3 7.4  
Changes at Ship Shoal 349 Field (Mahogany)          
Reserve Quantities [Line Items]          
Revisions of previous estimates       7.4  
Extensions and discoveries   3.5      
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  
Changes at the Fairway Field          
Reserve Quantities [Line Items]          
Revisions of previous estimates   1.0 1.5 1.1  
Changes Due to Price          
Reserve Quantities [Line Items]          
Revisions of previous estimates   3.4 1.2 10.7  
Changes at the Yellow Rose Field          
Reserve Quantities [Line Items]          
Proved estimated reserve at the date of sale 19.0        
Changes at the Viosca Knoll 823          
Reserve Quantities [Line Items]          
Revisions of previous estimates     3.8    
Changes at the Mississippi Canyon 782 field          
Reserve Quantities [Line Items]          
Revisions of previous estimates     1.3    
Changes at the Main Pass 108 field          
Reserve Quantities [Line Items]          
Revisions of previous estimates     1.2    
Mississippi Canyon 698 (Big Bend)          
Reserve Quantities [Line Items]          
Revisions of previous estimates   1.1      
Ewing Bank 910 Field          
Reserve Quantities [Line Items]          
Revisions of previous estimates   0.8      
Viosca Knoll 783 (Virgo) Field          
Reserve Quantities [Line Items]          
Revisions of previous estimates   0.8      
Main Pass 286 Field          
Reserve Quantities [Line Items]          
Extensions and discoveries   1.5      
[1] Primarily related to upward revisions of 6.2 MMBoe, which included upwards revisions of 1.1 MMBoe at our Mississippi Canyon 698 (Big Bend) field, 1.0 MMBoe at our Fairway field, 0.8 MMBoe at our Ewing Bank 910 field and 0.8 MMBoe at our Viosca Knoll 783 (Virgo) field. Additionally, increases of 3.4 MMBoe were due to price revisions.
[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] Primarily related to upward revisions of 14.2 MMBoe, which included upward revisions of 3.8 MMBoe at our Viosca Knoll 823 (Tahoe/SE Tahoe) field, 1.5 MMBoe at our Fairway field, 1.3 MMBoe at our Mississippi Canyon 782 (Dantzler) field, and 1.2 MMBoe at our Main Pass 108 field. Partially offsetting were decreases for price revisions of 1.2 MMBoe.
[4] 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.
[5] Primarily related to extensions and discoveries at our Ship Shoal 349 (Mahogany) field of 3.5 MMBoe and at our Main Pass 286 field of 1.5 MMBoe.
[6] Primarily due to increases at our Ewing Bank 910 field.
[7] We believe that we will be able to develop all but 1.8 MMBoe (approximately 15%) of the total of 12.0 MMBoe reserves classified as proved undeveloped (“PUDs”) at December 31, 2017, within five years from the date such reserves were initially recorded. The lone exceptions are 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. Two sidetrack PUD locations in this field will be delayed until an existing well is depleted and available to sidetrack. Based on the latest reserve report, these PUD locations are expected to be developed in 2023.