Derivatives Derivatives (Schedule of Non-designated Hedges Outstanding) (Details)	12 Months Ended
	Dec. 31, 2017 MMBTU $ / Unit bbl
Natural gas | Swap | If Nymex | Jan'18 - Dec'18
Derivative Instruments, Gain (Loss) [Line Items]
Hedged Volume (Mmbtu) | MMBTU	20,000
Swap Price	3.013
Natural gas | Swap | If Nymex | Apr'18 - Oct'18
Derivative Instruments, Gain (Loss) [Line Items]
Hedged Volume (Mmbtu) | MMBTU	10,000
Swap Price	2.990
Natural gas | Basis Swap | If Nymex | Jan'18 - Mar'18
Derivative Instruments, Gain (Loss) [Line Items]
Hedged Volume (Mmbtu) | MMBTU	10,000
Swap Price	(0.208)
Natural gas | Basis Swap | If Nymex | Nov'18 - Dec'18
Derivative Instruments, Gain (Loss) [Line Items]
Hedged Volume (Mmbtu) | MMBTU	10,000
Swap Price	(0.208)
Natural gas | Three-way collar | If Nymex | Jan'18 - Mar'18
Derivative Instruments, Gain (Loss) [Line Items]
Hedged Volume (Mmbtu) | MMBTU	60,000
Floor Price	3.29
Ceiling Price	4.07
Subfloor Price	2.63
Natural gas | Three-way collar | If Nymex | Apr'18 - Dec'18
Derivative Instruments, Gain (Loss) [Line Items]
Hedged Volume (Mmbtu) | MMBTU	20,000
Floor Price	3.00
Ceiling Price	3.51
Subfloor Price	2.50
Crude Oil | Swap | Wti Nymex | Jan'18 - Dec'18
Derivative Instruments, Gain (Loss) [Line Items]
Hedged Volume (Bbl) | bbl	3,000
Swap Price	51.36
Crude Oil | Collar | Wti Nymex | Jan'18 - Mar'18
Derivative Instruments, Gain (Loss) [Line Items]
Hedged Volume (Bbl) | bbl	500
Floor Price	55.00
Ceiling Price	59.50
Crude Oil | Three-way collar | Wti Nymex | Jan'18 - Dec'18
Derivative Instruments, Gain (Loss) [Line Items]
Hedged Volume (Bbl) | bbl	2,000
Floor Price	47.50
Ceiling Price	56.08
Subfloor Price	37.50
Liquids | Swap | OPIS - Mont Belvieu | Apr'18 - Sep'18
Derivative Instruments, Gain (Loss) [Line Items]
Hedged Volume (Bbl) | bbl	1,000
Swap Price	31.16