Derivative Financial Instruments - Summary of Outstanding Oil and Gas Derivative Contracts and Weighted Average Oil and Gas Prices (Details)	Dec. 31, 2017 MBbls $ / MBbls	Dec. 31, 2016 MBbls $ / MBbls	Dec. 31, 2015 MBbls
Midland-Cushing Index | Basis Swap Contracts
Derivative [Line Items]
Notional			5,806
Forecast | Crude Oil (MBbls) | Basis Swap Contracts
Derivative [Line Items]
Price differential ($/Bbl) | $ / MBbls	(1.03)	(0.87)
Forecast | Crude Oil (MBbls) | Midland-Cushing Index | Basis Swap Contracts
Derivative [Line Items]
Notional	4,290	1,516
Forecast | Crude Oil (MBbls) | Purchased | Put Option
Derivative [Line Items]
Notional	2,334	7,950
Weighted average strike price | $ / MBbls	53.46	49.74
Forecast | Crude Oil (MBbls) | Sold | Put Option
Derivative [Line Items]
Notional	(2,334)	(7,950)
Weighted average strike price | $ / MBbls	38.46	35.83