Derivative Financial Instruments Derivative Financial Instruments (Schedule of Gas Derivative Contracts Volume and Weighted Average Prices) (Details)	Jul. 31, 2017 MMBTU / d $ / MMBTU	Jun. 30, 2017 MMBTU / d $ / MMBTU
Collar Contracts With Short Puts For Third Quarter of Year One [Member] | Gas contracts, in MMBTU [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount | MMBTU / d		290,000
Collar Contracts With Short Puts For Third Quarter of Year One [Member] | Gas contracts, price per MMBTU [Member]
Derivative [Line Items]
Derivative, Average Cap Price		3.57
Derivative, Average Floor Price		2.95
Derivative, Notional Amount, Price Per Unit		2.47
Collar Contracts With Short Puts For Fourth Quarter of Year One [Member] | Gas contracts, in MMBTU [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount | MMBTU / d		300,000
Collar Contracts With Short Puts For Fourth Quarter of Year One [Member] | Gas contracts, price per MMBTU [Member]
Derivative [Line Items]
Derivative, Average Cap Price		3.60
Derivative, Average Floor Price		2.96
Derivative, Notional Amount, Price Per Unit		2.47
Collar Contracts With Short Puts for Year 2 [Member] | Gas contracts, in MMBTU [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount | MMBTU / d		62,329
Collar Contracts With Short Puts for Year 2 [Member] | Gas contracts, price per MMBTU [Member]
Derivative [Line Items]
Derivative, Average Cap Price		3.56
Derivative, Average Floor Price		2.91
Derivative, Notional Amount, Price Per Unit		2.37
Mid-Continent [Member] | Basis Swap Contracts for Third Quarter of Year One [Member] | Gas contracts, in MMBTU [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount | MMBTU / d		45,000
Mid-Continent [Member] | Basis Swap Contracts for Third Quarter of Year One [Member] | Gas contracts, price per MMBTU [Member]
Derivative [Line Items]
Derivative, Swap Type, Price Differential		(0.32)
Mid-Continent [Member] | Basis Swap Contracts for Fourth Quarter of Year One [Member] | Gas contracts, in MMBTU [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount | MMBTU / d		45,000
Mid-Continent [Member] | Basis Swap Contracts for Fourth Quarter of Year One [Member] | Gas contracts, price per MMBTU [Member]
Derivative [Line Items]
Derivative, Swap Type, Price Differential		(0.32)
Mid-Continent [Member] | Basis Swap Contracts for Year 2 [Member] | Gas contracts, in MMBTU [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount | MMBTU / d		0
Mid-Continent [Member] | Basis Swap Contracts for Year 2 [Member] | Gas contracts, price per MMBTU [Member]
Derivative [Line Items]
Derivative, Swap Type, Price Differential		0.00
Permian Basin [Member] | Basis Swap Contracts for Third Quarter of Year One [Member] | Gas contracts, in MMBTU [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount | MMBTU / d		0
Permian Basin [Member] | Basis Swap Contracts for Third Quarter of Year One [Member] | Gas contracts, price per MMBTU [Member]
Derivative [Line Items]
Derivative, Swap Type, Price Differential		0.00
Permian Basin [Member] | Basis Swap Contracts for Fourth Quarter of Year One [Member] | Gas contracts, in MMBTU [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount | MMBTU / d		26,522
Permian Basin [Member] | Basis Swap Contracts for Fourth Quarter of Year One [Member] | Gas contracts, price per MMBTU [Member]
Derivative [Line Items]
Derivative, Swap Type, Price Differential		0.30
Permian Basin [Member] | Basis Swap Contracts for Year 2 [Member] | Gas contracts, in MMBTU [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount | MMBTU / d		39,945
Permian Basin [Member] | Basis Swap Contracts for Year 2 [Member] | Gas contracts, price per MMBTU [Member]
Derivative [Line Items]
Derivative, Swap Type, Price Differential		0.30
Permian Basin [Member] | Subsequent Event [Member] | Basis Swap Contracts for Third Quarter of Year One [Member] | Gas contracts, in MMBTU [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount | MMBTU / d	6,739
Permian Basin [Member] | Subsequent Event [Member] | Basis Swap Contracts for Third Quarter of Year One [Member] | Gas contracts, price per MMBTU [Member]
Derivative [Line Items]
Derivative, Swap Type, Price Differential	0.26
Permian Basin [Member] | Subsequent Event [Member] | Basis Swap Contracts for Year 2 [Member] | Gas contracts, in MMBTU [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount | MMBTU / d	11,726
Permian Basin [Member] | Subsequent Event [Member] | Basis Swap Contracts for Year 2 [Member] | Gas contracts, price per MMBTU [Member]
Derivative [Line Items]
Derivative, Swap Type, Price Differential	0.31