Derivative Financial Instruments (Schedule of NGL Derivative Contracts Volume and Weighted Average Prices) (Details) - Ethane	Mar. 31, 2018 bbl / d MMBTU / d $ / MMBTU
NGL contract, MMBtu Equivalent
Derivative [Line Items]
Volume, barrels per day	6,920
NGL contract, MMBtu Equivalent | Basis Swap Contracts for Q2
Derivative [Line Items]
Volume, barrels per day	6,920
NGL contract, MMBtu Equivalent | Basis Swap Contracts for Q3
Derivative [Line Items]
Volume, barrels per day	6,920
NGL contract, MMBtu Equivalent | Basis swap contracts for Q4
Derivative [Line Items]
Volume, barrels per day	6,920
NGL contract, MMBtu Equivalent | Basis swap contracts for next year
Derivative [Line Items]
Volume, barrels per day	6,920
NGL contract, price per MMBtu Equivalent | Basis Swap Contracts for Q2
Derivative [Line Items]
Price differential, dollars per barrel | $ / MMBTU	1.60
NGL contract, price per MMBtu Equivalent | Basis Swap Contracts for Q3
Derivative [Line Items]
Price differential, dollars per barrel | $ / MMBTU	1.60
NGL contract, price per MMBtu Equivalent | Basis swap contracts for Q4
Derivative [Line Items]
Price differential, dollars per barrel | $ / MMBTU	1.60
NGL contract, price per MMBtu Equivalent | Basis swap contracts for next year
Derivative [Line Items]
Price differential, dollars per barrel | $ / MMBTU	1.60
NGL contract, in BBLS
Derivative [Line Items]
Volume, barrels per day | bbl / d	2,500