Quarterly report pursuant to Section 13 or 15(d)

Crude Oil and Natural Gas Properties and Equipment (Crude Oil and Natural Gas Properties and Equipment) (Details)

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Crude Oil and Natural Gas Properties and Equipment (Crude Oil and Natural Gas Properties and Equipment) (Details) - USD ($)
$ in Thousands
Mar. 31, 2021
Dec. 31, 2020
Property, Plant and Equipment [Line Items]    
Gross crude oil and natural gas properties and equipment $ 517,770 $ 472,800
Accumulated depreciation, depletion, amortization and impairment (439,578) (435,764)
Net crude oil and natural gas properties, equipment and other 78,192 37,036
Wells, Platforms and Other Production Facilities [Member]    
Property, Plant and Equipment [Line Items]    
Gross crude oil and natural gas properties and equipment 477,477 441,879
Work-in-Progress [Member]    
Property, Plant and Equipment [Line Items]    
Gross crude oil and natural gas properties and equipment 542 169
Undeveloped Acreage [Member]    
Property, Plant and Equipment [Line Items]    
Gross crude oil and natural gas properties and equipment 23,735 21,476
Equipment and Other [Member]    
Property, Plant and Equipment [Line Items]    
Gross crude oil and natural gas properties and equipment $ 16,016 $ 9,276