Derivative Instruments (Schedule of NGL Derivative Positions) (Details) - Q3 - Q4 2018 - Natural Gas Liquids - Fixed Price Swaps	Jun. 30, 2018 bbl / d $ / bbls
OPIS Purity Ethane Mont Belvieu Non-TET
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount | bbl / d	2,200
Weighted Average Fixed Price ($/Bbl) | $ / bbls	12.01
OPIS Propane Mont Belvieu Non-TET
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount | bbl / d	1,500
Weighted Average Fixed Price ($/Bbl) | $ / bbls	34.23
OPIS Normal Butane Mont Belvieu Non-TET
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount | bbl / d	200
Weighted Average Fixed Price ($/Bbl) | $ / bbls	38.85
OPIS Isobutane Mont Belvieu Non-TET
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount | bbl / d	600
Weighted Average Fixed Price ($/Bbl) | $ / bbls	38.98
OPIS Natural Gasoline Mont Belvieu Non-TET
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount | bbl / d	600
Weighted Average Fixed Price ($/Bbl) | $ / bbls	55.23