Derivative Financial Instruments (Schedule of Gas Derivative Contracts Volume and Weighted Average Prices) (Details)	May 04, 2018 MMBTU / d $ / MMBTU	Mar. 31, 2018 MMBTU / d $ / MMBTU
Swap contracts for Q2 | Gas contracts, in MMBTU
Derivative [Line Items]
Volume, barrels per day | MMBTU / d		100,000
Swap contracts for Q2 | Gas contracts, price per MMBTU
Derivative [Line Items]
Price per MMBtu in usd		3.00
Swap contracts for Q3 | Gas contracts, in MMBTU
Derivative [Line Items]
Volume, barrels per day | MMBTU / d		100,000
Swap contracts for Q3 | Gas contracts, price per MMBTU
Derivative [Line Items]
Price per MMBtu in usd		3.00
Swap contracts for Q4 | Gas contracts, in MMBTU
Derivative [Line Items]
Volume, barrels per day | MMBTU / d		100,000
Swap contracts for Q4 | Gas contracts, price per MMBTU
Derivative [Line Items]
Price per MMBtu in usd		3.00
Swap contracts for next year | Gas contracts, in MMBTU
Derivative [Line Items]
Volume, barrels per day | MMBTU / d		0
Swap contracts for next year | Gas contracts, price per MMBTU
Derivative [Line Items]
Price per MMBtu in usd		0.00
Collar contracts with short puts for Q2 | Gas contracts, in MMBTU
Derivative [Line Items]
Volume, barrels per day | MMBTU / d		50,000
Collar contracts with short puts for Q2 | Gas contracts, price per MMBTU
Derivative [Line Items]
Ceiling, price per barrel		3.40
Floor, price per barrel		2.75
Short put, price per barrel		2.25
Collar contracts with short puts for Q3 | Gas contracts, in MMBTU
Derivative [Line Items]
Volume, barrels per day | MMBTU / d		50,000
Collar contracts with short puts for Q3 | Gas contracts, price per MMBTU
Derivative [Line Items]
Ceiling, price per barrel		3.40
Floor, price per barrel		2.75
Short put, price per barrel		2.25
Collar contracts with short puts for Q4 | Gas contracts, in MMBTU
Derivative [Line Items]
Volume, barrels per day | MMBTU / d		50,000
Collar contracts with short puts for Q4 | Gas contracts, price per MMBTU
Derivative [Line Items]
Ceiling, price per barrel		3.40
Floor, price per barrel		2.75
Short put, price per barrel		2.25
Collar contracts with short puts for next year | Gas contracts, in MMBTU
Derivative [Line Items]
Volume, barrels per day | MMBTU / d		0
Collar contracts with short puts for next year | Gas contracts, price per MMBTU
Derivative [Line Items]
Ceiling, price per barrel		0.00
Floor, price per barrel		0.00
Short put, price per barrel		0.00
Basis Swap Contracts for Q2 | Gas contracts, in MMBTU | Southern California
Derivative [Line Items]
Volume, barrels per day | MMBTU / d		40,000
Basis Swap Contracts for Q2 | Gas contracts, price per MMBTU | Southern California
Derivative [Line Items]
Price differential, dollars per barrel		0.30
Basis Swap Contracts for Q3 | Gas contracts, in MMBTU | Southern California
Derivative [Line Items]
Volume, barrels per day | MMBTU / d		80,000
Basis Swap Contracts for Q3 | Gas contracts, price per MMBTU | Southern California
Derivative [Line Items]
Price differential, dollars per barrel		0.30
Basis swap contracts for Q4 | Gas contracts, in MMBTU | Southern California
Derivative [Line Items]
Volume, barrels per day | MMBTU / d		66,522
Basis swap contracts for Q4 | Gas contracts, price per MMBTU | Southern California
Derivative [Line Items]
Price differential, dollars per barrel		0.50
Basis swap contracts for next year | Gas contracts, in MMBTU | Southern California
Derivative [Line Items]
Volume, barrels per day | MMBTU / d		84,932
Basis swap contracts for next year | Gas contracts, price per MMBTU | Southern California
Derivative [Line Items]
Price differential, dollars per barrel		0.33
Basis Swap Contracts for July 2018 Through September 2019 | Gas contracts, in MMBTU | Southern California | Subsequent event
Derivative [Line Items]
Volume, barrels per day | MMBTU / d	20,000
Price differential, dollars per barrel	1.54
Basis Swap Contracts for January 2019 Through September 2019 | Gas contracts, in MMBTU | Southern California | Subsequent event
Derivative [Line Items]
Volume, barrels per day | MMBTU / d	30,000
Price differential, dollars per barrel	1.47