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Restricted Investments - Restricted Investment Balances (Detail) - USD ($)
$ in Thousands
Dec. 31, 2020
Dec. 31, 2019
Schedule Of Investments [Line Items]    
Restricted investments $ 4,623 $ 4,622
BOEM platform abandonment [Member]    
Schedule Of Investments [Line Items]    
Restricted investments 313 313
SPBPC Collateral Contractual pipeline and surface facilities abandonment [Member]    
Schedule Of Investments [Line Items]    
Restricted investments $ 4,310 $ 4,309