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
 12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
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 11.00%      
Barrel Equivalent        
Reserve Quantities [Line Items]        
Revisions of previous estimates [2] 21.1 [1] 9.6 [3] 13.0 [4]  
Extensions and discoveries [2] 2.1 [5] 5.2 [6]    
Proved reserves [2] 84.0 74.2 74.0 76.4
Barrel Equivalent | Proved Undeveloped Reserves        
Reserve Quantities [Line Items]        
Proved reserves [2] 17.0 [7] 12.0 9.3  
Changes at the Viosca Knoll 823        
Reserve Quantities [Line Items]        
Revisions of previous estimates     3.8  
Extensions and discoveries 1.3      
Changes at the Fairway Field        
Reserve Quantities [Line Items]        
Revisions of previous estimates   1.0 1.5  
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  
Changes Due To Price        
Reserve Quantities [Line Items]        
Revisions of previous estimates 2.3 3.4 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    
Extensions and discoveries 0.7      
Viosca Knoll 783 (Tahoe/SE Tahoe) Field        
Reserve Quantities [Line Items]        
Revisions of previous estimates   0.8    
Changes at Ship Shoal 349 Field (Mahogany)        
Reserve Quantities [Line Items]        
Extensions and discoveries   3.5    
Main Pass 286 Field        
Reserve Quantities [Line Items]        
Extensions and discoveries   1.5    
Mahogany Field        
Reserve Quantities [Line Items]        
Revisions of previous estimates 13.8      
Ship Shoal 028 Field        
Reserve Quantities [Line Items]        
Revisions of previous estimates 5.4      
Mississippi Canyon 243 Field        
Reserve Quantities [Line Items]        
Wells expected to be drilled, year 2021      
Virgo Deepwater Fields        
Reserve Quantities [Line Items]        
Wells expected to be drilled, year 2022      
[1] Primarily related to upward revisions of 13.8 MMBoe at our Mahogany field and of 5.4 MMBoe at our Ship Shoal 028 field. Additionally, increases of 2.3 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 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 (Tahoe/SE Tahoe) field. Additionally, increases of 3.4 MMBoe were due to price revisions.
[4] Primarily related to upward revisions of 14.2 MMBoe, which included upward revisions of 3.8 MMBoe at our Virgo 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.
[5] Primarily related to extensions and discoveries of 1.3 MMBoe at our Virgo field and 0.7 MMBoe at our Ewing Bank 910 field.
[6] 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.
[7] We believe that we will be able to develop all but 1.8 MMBoe (approximately 11%) of the total of 17.0 MMBoe reserves classified as proved undeveloped (“PUDs”) at December 31, 2018, within five years from the date such reserves were initially recorded. The lone exceptions are at the Mississippi Canyon 243 field (Matterhorn) and Virgo deepwater fields where future development drilling has been planned as sidetracks of existing wellbores due to conductor slot limitations and rig availability. Two sidetrack PUD locations, one in each 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 2021 and 2022, respectively.