v3.26.3
Derivative Financial Instruments - Schedule of Location of Gain (Details) - USD ($)
$ in Thousands
 3 Months Ended 9 Months Ended
Sep. 30, 2026
Sep. 30, 2025
Sep. 30, 2026
Sep. 30, 2025
Derivative instruments, Location of Gain/(Loss)        
Total derivatives not designated as hedging instruments $ (107,014) $ 2,792 $ (369,306) $ 10,675
Provisional sales contracts | Income Statement Location [Axis]: us-gaap:Revenues        
Derivative instruments, Location of Gain/(Loss)        
Total derivatives not designated as hedging instruments 26,862 (964) (35,243) (8,571)
Commodity | Income Statement Location [Axis]: kos:GainLossOnCommodityDerivativeInstrumentsNetPretax        
Derivative instruments, Location of Gain/(Loss)        
Total derivatives not designated as hedging instruments (133,876) 3,646 (334,063) 18,480
Interest rate | Income Statement Location [Axis]: kos:InterestExpenseIncomeNet        
Derivative instruments, Location of Gain/(Loss)        
Total derivatives not designated as hedging instruments $ 0 $ 110 $ 0 $ 766