Derivative Financial Instruments Derivative Financial Instruments (Schedule of Gas Derivative Contracts Volume and Weighted Average Prices) (Details)	Sep. 30, 2015 MMBTU / d $ / MMBTU
Collar Contracts With Short Puts for Current Year [Member] | Gas contracts, in MMBTU [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount | MMBTU / d	285,000
Collar Contracts With Short Puts for Current Year [Member] | Gas contracts, price per MMBTU [Member]
Derivative [Line Items]
Derivative, Average Cap Price	5.07
Derivative, Average Floor Price	4.00
Collar Contracts With Short Puts for Current Year [Member] | Gas contracts, price per MMBTU [Member] | Short Put [Member]
Derivative [Line Items]
Derivative, Notional Amount, Price Per Unit	3.00
Collar Contracts With Short Puts for Year 2 [Member] | Gas contracts, in MMBTU [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount | MMBTU / d	180,000
Collar Contracts With Short Puts for Year 2 [Member] | Gas contracts, price per MMBTU [Member]
Derivative [Line Items]
Derivative, Average Cap Price	4.01
Derivative, Average Floor Price	3.24
Collar Contracts With Short Puts for Year 2 [Member] | Gas contracts, price per MMBTU [Member] | Short Put [Member]
Derivative [Line Items]
Derivative, Notional Amount, Price Per Unit	2.78
Collar Contracts With Short Puts for Year 3 [Member] | Gas contracts, in MMBTU [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount | MMBTU / d	0
Collar Contracts With Short Puts for Year 3 [Member] | Gas contracts, price per MMBTU [Member]
Derivative [Line Items]
Derivative, Average Cap Price	0.00
Derivative, Average Floor Price	0.00
Collar Contracts With Short Puts for Year 3 [Member] | Gas contracts, price per MMBTU [Member] | Short Put [Member]
Derivative [Line Items]
Derivative, Notional Amount, Price Per Unit	0.00
Swap Contracts for Current Year [Member] | Gas contracts, in MMBTU [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount | MMBTU / d	20,000
Swap Contracts for Current Year [Member] | Gas contracts, price per MMBTU [Member]
Derivative [Line Items]
Derivative, Swap Type, Average Fixed Price	4.31
Swap Contracts for Year 2 [Member] | Gas contracts, in MMBTU [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount | MMBTU / d	70,000
Swap Contracts for Year 2 [Member] | Gas contracts, price per MMBTU [Member]
Derivative [Line Items]
Derivative, Swap Type, Average Fixed Price	4.06
Swap Contracts for Year 3 [Member] | Gas contracts, in MMBTU [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount | MMBTU / d	0
Swap Contracts for Year 3 [Member] | Gas contracts, price per MMBTU [Member]
Derivative [Line Items]
Derivative, Swap Type, Average Fixed Price	0.00
Gulf Coast [Member] | Basis Swap Contracts for Current Year [Member] | Gas contracts, in MMBTU [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount | MMBTU / d	20,000
Gulf Coast [Member] | Basis Swap Contracts for Current Year [Member] | Gas contracts, price per MMBTU [Member]
Derivative [Line Items]
Derivative, Swap Type, Average Fixed Price	0.00
Gulf Coast [Member] | Basis Swap Contracts for Year 2 [Member] | Gas contracts, in MMBTU [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount | MMBTU / d	10,000	[1]
Gulf Coast [Member] | Basis Swap Contracts for Year 2 [Member] | Gas contracts, price per MMBTU [Member]
Derivative [Line Items]
Derivative, Swap Type, Average Fixed Price	0.00
Gulf Coast [Member] | Basis Swap Contracts for Year 3 [Member] | Gas contracts, in MMBTU [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount | MMBTU / d	0	[1]
Gulf Coast [Member] | Basis Swap Contracts for Year 3 [Member] | Gas contracts, price per MMBTU [Member]
Derivative [Line Items]
Derivative, Swap Type, Average Fixed Price	0.00
Mid-Continent [Member] | Basis Swap Contracts for Current Year [Member] | Gas contracts, in MMBTU [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount | MMBTU / d	95,000
Mid-Continent [Member] | Basis Swap Contracts for Current Year [Member] | Gas contracts, price per MMBTU [Member]
Derivative [Line Items]
Derivative, Swap Type, Average Fixed Price	(0.24)
Mid-Continent [Member] | Basis Swap Contracts for Year 2 [Member] | Gas contracts, in MMBTU [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount | MMBTU / d	15,000	[1]
Mid-Continent [Member] | Basis Swap Contracts for Year 2 [Member] | Gas contracts, price per MMBTU [Member]
Derivative [Line Items]
Derivative, Swap Type, Average Fixed Price	(0.32)
Mid-Continent [Member] | Basis Swap Contracts for Year 3 [Member] | Gas contracts, in MMBTU [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount | MMBTU / d	45,000	[1],[2]
Mid-Continent [Member] | Basis Swap Contracts for Year 3 [Member] | Gas contracts, price per MMBTU [Member]
Derivative [Line Items]
Derivative, Swap Type, Average Fixed Price	(0.32)
Permian Basin [Member] | Basis Swap Contracts for Current Year [Member] | Gas contracts, in MMBTU [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount | MMBTU / d	10,000
Permian Basin [Member] | Basis Swap Contracts for Current Year [Member] | Gas contracts, price per MMBTU [Member]
Derivative [Line Items]
Derivative, Swap Type, Average Fixed Price	(0.13)
Permian Basin [Member] | Basis Swap Contracts for Year 2 [Member] | Gas contracts, in MMBTU [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount | MMBTU / d	0	[1]
Permian Basin [Member] | Basis Swap Contracts for Year 2 [Member] | Gas contracts, price per MMBTU [Member]
Derivative [Line Items]
Derivative, Swap Type, Average Fixed Price	0.00
Permian Basin [Member] | Basis Swap Contracts for Year 3 [Member] | Gas contracts, in MMBTU [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount | MMBTU / d	0	[1]
Permian Basin [Member] | Basis Swap Contracts for Year 3 [Member] | Gas contracts, price per MMBTU [Member]
Derivative [Line Items]
Derivative, Swap Type, Average Fixed Price	0.00
Permian Basin [Member] | So Cal Basis Swap Contracts for Current Year [Member] | Gas contracts, in MMBTU [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount | MMBTU / d	30,000
Permian Basin [Member] | So Cal Basis Swap Contracts for Current Year [Member] | Gas contracts, price per MMBTU [Member]
Derivative [Line Items]
Derivative, Swap Type, Average Fixed Price	0.19
Permian Basin [Member] | So Cal Basis Swap Contracts for Year 2 [Member] | Gas contracts, in MMBTU [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount | MMBTU / d	0
Permian Basin [Member] | So Cal Basis Swap Contracts for Year 2 [Member] | Gas contracts, price per MMBTU [Member]
Derivative [Line Items]
Derivative, Swap Type, Average Fixed Price	0.00
Permian Basin [Member] | So Cal Basis Swap Contracts for Year 3 [Member] | Gas contracts, in MMBTU [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount | MMBTU / d	0
Permian Basin [Member] | So Cal Basis Swap Contracts for Year 3 [Member] | Gas contracts, price per MMBTU [Member]
Derivative [Line Items]
Derivative, Swap Type, Average Fixed Price	0.00

[1] (a)Represent swaps that fix the basis differentials between the index prices at which the Company sells its Gulf Coast, Mid-Continent and Permian Basin gas, respectively, and the HH index price used in gas swap and collar contracts.

[2] (b)