Annual report pursuant to Section 13 and 15(d)

Derivative Instruments and Hedging Activities (Schedule of Outstanding Oil and Natural Gas Derivative Contracts) (Details)

v3.8.0.1
Derivative Instruments and Hedging Activities (Schedule of Outstanding Oil and Natural Gas Derivative Contracts) (Details) - Forecast - Not Designated as Hedging Instrument
 12 Months Ended
Dec. 31, 2019
MMBTU
$ / MMBTU
MBbls
Dec. 31, 2018
MMBTU
$ / MMBTU
MBbls
Oil | Collar contracts (two-way collars)    
Derivative [Line Items]    
Total volume (MBbls) | MBbls 0 365,000
Oil | Collar contracts (two-way collars) | Call option | Short    
Derivative [Line Items]    
Strike price (in dollars per share) 0 60.50
Oil | Collar contracts (two-way collars) | Put option | Long    
Derivative [Line Items]    
Strike price (in dollars per share) 0 50
Oil | Collar contracts combined with short puts (three-way collars)    
Derivative [Line Items]    
Total volume (MBbls) | MBbls 730,000 3,468,000
Oil | Collar contracts combined with short puts (three-way collars) | Call option | Short    
Derivative [Line Items]    
Strike price (in dollars per share) 58.50 60.86
Oil | Collar contracts combined with short puts (three-way collars) | Put option | Short    
Derivative [Line Items]    
Strike price (in dollars per share) 40 39.21
Oil | Collar contracts combined with short puts (three-way collars) | Put option | Long    
Derivative [Line Items]    
Strike price (in dollars per share) 50 48.95
Oil | Collar contracts combined with short puts (WTI, three-way collars), Subsequent contracts    
Derivative [Line Items]    
Total volume (MBbls) | MBbls 1,095,000 0
Oil | Collar contracts combined with short puts (WTI, three-way collars), Subsequent contracts | Call option | Short    
Derivative [Line Items]    
Strike price (in dollars per share) 65 0
Oil | Collar contracts combined with short puts (WTI, three-way collars), Subsequent contracts | Put option | Short    
Derivative [Line Items]    
Strike price (in dollars per share) 45 0
Oil | Collar contracts combined with short puts (WTI, three-way collars), Subsequent contracts | Put option | Long    
Derivative [Line Items]    
Strike price (in dollars per share) 55 0
Oil | Swap contracts    
Derivative [Line Items]    
Total volume (MBbls) | MBbls 0 2,009,000
Average swap price (in dollars per share) 0.00 51.78
Oil | Swap contracts | Oil contracts (Midland basis differential)    
Derivative [Line Items]    
Total volume (MBbls) | MBbls 0 5,289,000
Average swap price (in dollars per share) 0.00 0.86
Natural gas | Collar contracts (Henry Hub, two-way collars)    
Derivative [Line Items]    
Total volume (BBtu) | MMBTU 0 720,000
Natural gas | Collar contracts (Henry Hub, two-way collars) | Call option | Short    
Derivative [Line Items]    
Strike price (in dollars per share) 0 3.84
Natural gas | Collar contracts (Henry Hub, two-way collars) | Put option | Long    
Derivative [Line Items]    
Strike price (in dollars per share) 0 3.40
Natural gas | Swap contracts | Swap contracts (Henry Hub), Subsequent contracts    
Derivative [Line Items]    
Strike price (in dollars per share) 0 2.95
Total volume (BBtu) | MMBTU 0 3,366,000