Quarterly report pursuant to Section 13 or 15(d)

Derivative Instruments and Hedging Activities (Oil contracts (Midland basis differential)) (Details)

v3.7.0.1
Derivative Instruments and Hedging Activities (Oil contracts (Midland basis differential)) (Details) - Not Designated as Hedging Instrument - Oil - Swap contracts - Forecast
 6 Months Ended 12 Months Ended
Dec. 31, 2017
$ / MMBTU
MBbls
Dec. 31, 2018
$ / MMBTU
MBbls
Derivative [Line Items]    
Total volume (MBbls) | MBbls 368,000 0
Average swap price (in dollars per share) | $ / MMBTU (45.74) (0.00)
Oil contracts (Midland basis differential)    
Derivative [Line Items]    
Total volume (MBbls) | MBbls 1,104,000 2,190,000
Average swap price (in dollars per share) | $ / MMBTU (0.52) (1.02)
Oil contracts (Midland basis differential) | Subsequent Event    
Derivative [Line Items]    
Total volume (MBbls) | MBbls 0 548,000
Average swap price (in dollars per share) | $ / MMBTU (0.00) (1.05)
Oil contracts (WTI) | Subsequent Event    
Derivative [Line Items]    
Total volume (MBbls) | MBbls 0 730,000
Average swap price (in dollars per share) | $ / MMBTU (0.00) (50.03)