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Debt - Letters of Credit (Details)
$ in Millions
Oct. 31, 2020
USD ($)
Dec. 31, 2019
USD ($)
letter_of_credit
Block 11 Offshore Sao Tome And Principe | Subsequent Event    
Debt Instrument [Line Items]    
Amount outstanding $ 3.4  
Letter of credit arrangement    
Debt Instrument [Line Items]    
Number of letters of credit | letter_of_credit   2
Amount outstanding   $ 20.4