Derivative Financial Instruments (Narrative) (Details)	Dec. 31, 2020 bbl / d $ / MMBTU
Oil contracts | Brent Swap Contracts for Second Quarter of year One [Member]
Debt and Equity Securities, FV-NI [Line Items]
Derivative, Nonmonetary Notional Amount, Volume | bbl / d	85,000
Oil contracts | Brent Swap Contracts for Third Quarter of year One [Member]
Debt and Equity Securities, FV-NI [Line Items]
Derivative, Nonmonetary Notional Amount, Volume | bbl / d	0
Oil contracts | Brent Swap Contracts for Fourth Quarter of year One [Member]
Debt and Equity Securities, FV-NI [Line Items]
Derivative, Nonmonetary Notional Amount, Volume | bbl / d	0
Oil contracts | Brent Swap Contracts for year Two [Member]
Debt and Equity Securities, FV-NI [Line Items]
Derivative, Nonmonetary Notional Amount, Volume | bbl / d	0
Oil contracts | Brent Swap Contracts for First Quarter of year One [Member]
Debt and Equity Securities, FV-NI [Line Items]
Derivative, Nonmonetary Notional Amount, Volume | bbl / d	85,000
Oil contracts, price per bbl | Brent Swap Contracts for Second Quarter of year One [Member]
Debt and Equity Securities, FV-NI [Line Items]
Price per MMBtu in usd | $ / MMBTU	46.88
Oil contracts, price per bbl | Brent Swap Contracts for Third Quarter of year One [Member]
Debt and Equity Securities, FV-NI [Line Items]
Price per MMBtu in usd | $ / MMBTU	0
Oil contracts, price per bbl | Brent Swap Contracts for Fourth Quarter of year One [Member]
Debt and Equity Securities, FV-NI [Line Items]
Price per MMBtu in usd | $ / MMBTU	0
Oil contracts, price per bbl | Brent Swap Contracts for year Two [Member]
Debt and Equity Securities, FV-NI [Line Items]
Price per MMBtu in usd | $ / MMBTU	0
Oil contracts, price per bbl | Brent Swap Contracts for First Quarter of year One [Member]
Debt and Equity Securities, FV-NI [Line Items]
Price per MMBtu in usd | $ / MMBTU	46.88