Derivative Financial Instruments Derivative Financial Instruments (Schedule of Marketing Derivative Contracts Volume and Weighted Average Prices) (Details) (Details) (Basis Swap Contracts for Current Year [Member])	Mar. 31, 2014
Marketing Gas contracts, in MMBTU [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount	37,782
Marketing gas contracts, price per MMBTU [Member]
Derivative [Line Items]
Derivative, Swap Type, Average Fixed Price	0.31
Marketing Oil contracts, in BBL [Member]
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount	555
Marketing oil contracts, price per BBL [Member] [Member]
Derivative [Line Items]
Derivative, Swap Type, Average Fixed Price	5.55