v3.26.1
Derivative Financial Instruments - Schedule of Location of Gain (Details) - USD ($)
$ in Thousands
 3 Months Ended 6 Months Ended
Jun. 30, 2026
Jun. 30, 2025
Jun. 30, 2026
Jun. 30, 2025
Derivative instruments, Location of Gain/(Loss)        
Total derivatives not designated as hedging instruments $ 40,683 $ 15,469 $ (262,292) $ 7,883
Provisional sales contracts | Income Statement Location [Axis]: us-gaap:Revenues        
Derivative instruments, Location of Gain/(Loss)        
Total derivatives not designated as hedging instruments (11,126) (6,780) (62,105) (7,607)
Commodity | Income Statement Location [Axis]: kos:GainLossOnCommodityDerivativeInstrumentsNetPretax        
Derivative instruments, Location of Gain/(Loss)        
Total derivatives not designated as hedging instruments 51,809 21,566 (200,187) 14,834
Interest rate | Income Statement Location [Axis]: kos:InterestExpenseIncomeNet        
Derivative instruments, Location of Gain/(Loss)        
Total derivatives not designated as hedging instruments $ 0 $ 683 $ 0 $ 656