Derivative Financial Instruments Derivative Financial Instruments (Schedule of Gas Derivative Contracts Volume and Weighted Average Prices) (Details)	Sep. 30, 2014
Collar Contracts With Short Puts for Current Year [Member] | Gas contracts, in MMBTU [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount	115,000
Collar Contracts With Short Puts for Current Year [Member] | Gas contracts, price per MMBTU [Member]
Derivative [Line Items]
Derivative, Average Cap Price	4.70
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	285,000
Collar Contracts With Short Puts for Year 2 [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 Year 2 [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 3 [Member] | Gas contracts, in MMBTU [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount	20,000
Collar Contracts With Short Puts for Year 3 [Member] | Gas contracts, price per MMBTU [Member]
Derivative [Line Items]
Derivative, Average Cap Price	5.36
Derivative, Average Floor Price	4.00
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	3.00
Swap Contracts for Current Year [Member] | Gas contracts, in MMBTU [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount	195,000
Swap Contracts for Current Year [Member] | Gas contracts, price per MMBTU [Member]
Derivative [Line Items]
Derivative, Swap Type, Average Fixed Price	4.04
Swap Contracts for Year 2 [Member] | Gas contracts, in MMBTU [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount	20,000
Swap Contracts for Year 2 [Member] | Gas contracts, price per MMBTU [Member]
Derivative [Line Items]
Derivative, Swap Type, Average Fixed Price	4.31
Swap Contracts for Year 3 [Member] | Gas contracts, in MMBTU [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount	70,000
Swap Contracts for Year 3 [Member] | Gas contracts, price per MMBTU [Member]
Derivative [Line Items]
Derivative, Swap Type, Average Fixed Price	4.06
Mid-Continent [Member] | Basis Swap Contracts for Current Year [Member] | Gas contracts, in MMBTU [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount	120,000	[1]
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	(0.22)
Mid-Continent [Member] | Basis Swap Contracts for Year 2 [Member] | Gas contracts, in MMBTU [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount	95,000	[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	(0.24)
Mid-Continent [Member] | Basis Swap Contracts for Year 3 [Member] | Gas contracts, in MMBTU [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount	0	[1]
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	0.00
Permian Basin [Member] | Basis Swap Contracts for Current Year [Member] | Gas contracts, in MMBTU [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount	10,000	[1]
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	(0.15)
Permian Basin [Member] | Basis Swap Contracts for Year 2 [Member] | Gas contracts, in MMBTU [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount	10,000	[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	(0.13)
Permian Basin [Member] | Basis Swap Contracts for Year 3 [Member] | Gas contracts, in MMBTU [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount	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	16,630	[2]
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	0.34
Permian Basin [Member] | So Cal Basis Swap Contracts for Year 2 [Member] | Gas contracts, in MMBTU [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount	0	[2]
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	0	[2]
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 Mid-Continent and Permian Basin gas, respectively, and the NYMEX Henry Hub index price used in gas swap and collar contracts.

[2] (b)Represent swaps that fix the basis differentials between Permian Basin index prices and southern California index prices for Permian Basin gas forecasted for sale in southern California.