Quarterly report pursuant to Section 13 or 15(d)

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

v3.7.0.1
Derivative Instruments and Hedging Activities (Schedule of Outstanding Oil and Natural Gas Derivative Contracts) (Details) - Not Designated as Hedging Instrument - Forecast
6 Months Ended 12 Months Ended
Dec. 31, 2017
MMBTU
$ / MMBTU
MBbls
Dec. 31, 2018
MMBTU
$ / MMBTU
MBbls
Oil | Deferred premium put spread option    
Derivative [Line Items]    
Total volume (MBbls) | MBbls 506,000 0
Average swap price (in dollars per share) 2.45 0.00
Oil | Deferred premium put spread option | Put option | Short    
Derivative [Line Items]    
Strike price (in dollars per share) 40.00 0
Oil | Deferred premium put spread option | Put option | Long    
Derivative [Line Items]    
Strike price (in dollars per share) 50.00 0
Oil | Collar contracts (two-way collars)    
Derivative [Line Items]    
Total volume (MBbls) | MBbls 681,000 0
Oil | Collar contracts (two-way collars) | Put option | Long    
Derivative [Line Items]    
Strike price (in dollars per share) 47.50 0
Oil | Collar contracts (two-way collars) | Call option | Short    
Derivative [Line Items]    
Strike price (in dollars per share) 58.19 0
Oil | Call option contracts | Call option    
Derivative [Line Items]    
Total volume (MBbls) | MBbls 338,000 0
Strike price (in dollars per share) 1.82 0
Oil | Call option contracts | Call option | Short    
Derivative [Line Items]    
Strike price (in dollars per share) 50.00 0
Oil | Call option contracts | Call option | Long    
Derivative [Line Items]    
Strike price (in dollars per share) 50.00 0
Oil | Collar contracts combined with short puts (three-way collars)    
Derivative [Line Items]    
Total volume (MBbls) | MBbls 0 3,468,000
Oil | Collar contracts combined with short puts (three-way collars) | Put option | Short    
Derivative [Line Items]    
Strike price (in dollars per share) 0 39.21
Oil | Collar contracts combined with short puts (three-way collars) | Put option | Long    
Derivative [Line Items]    
Strike price (in dollars per share) 0 48.95
Oil | Collar contracts combined with short puts (three-way collars) | Call option | Short    
Derivative [Line Items]    
Strike price (in dollars per share) 0 60.86
Oil | Swap contracts    
Derivative [Line Items]    
Total volume (MBbls) | MBbls 368,000 0
Average swap price (in dollars per share) 45.74 0.00
Oil | Swap contracts | Swap contracts combined with short puts (enhanced swaps)    
Derivative [Line Items]    
Total volume (MBbls) | MBbls 368,000 0
Average swap price (in dollars per share) 44.50 0
Oil | Swap contracts | Swap contracts combined with short puts (enhanced swaps) | Put option | Short    
Derivative [Line Items]    
Strike price (in dollars per share) 30.00 0
Natural gas | Collar contracts combined with short puts (Henry Hub, three-way collars)    
Derivative [Line Items]    
Total volume (BBtu) | MMBTU 736,000 0
Natural gas | Collar contracts combined with short puts (Henry Hub, three-way collars) | Put option | Short    
Derivative [Line Items]    
Strike price (in dollars per share) 2.50 0
Natural gas | Collar contracts combined with short puts (Henry Hub, three-way collars) | Put option | Long    
Derivative [Line Items]    
Strike price (in dollars per share) 3.00 0
Natural gas | Collar contracts combined with short puts (Henry Hub, three-way collars) | Call option | Short    
Derivative [Line Items]    
Strike price (in dollars per share) 3.71 0
Natural gas | Collar contracts (Henry Hub, two-way collars)    
Derivative [Line Items]    
Total volume (BBtu) | MMBTU 1,224,000 720,000
Natural gas | Collar contracts (Henry Hub, two-way collars) | Put option | Long    
Derivative [Line Items]    
Strike price (in dollars per share) 3.16 3,400.00
Natural gas | Collar contracts (Henry Hub, two-way collars) | Call option | Short    
Derivative [Line Items]    
Strike price (in dollars per share) 3.74 3,840.00
Natural gas | Swap contracts    
Derivative [Line Items]    
Strike price (in dollars per share) 3.39 0
Total volume (BBtu) | MMBTU 492,000 0