Derivative Financial Instruments (Offsetting Assets and Liabilities) (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Derivative [Line Items]
Derivative Asset, Current	$ 75,237	$ 279,119
Derivative Asset, Noncurrent	90,854	55,257
Derivative Asset, Fair Value, Amount Not Offset Against Collateral		334,376
Derivative Liability, Current	11,626	13,416
Derivative Liability, Noncurrent	9,933	12,307
Not Designated As Hedging Instruments [Member]
Derivative [Line Items]
Derivative Asset, Fair Value, Amount Not Offset Against Collateral	166,091	334,376
Derivative Financial Instruments, Liabilities, Fair Value Disclosure	21,559	25,723
Derivative Noncurrent [Member] | Not Designated As Hedging Instruments [Member] | Commodity Price Derivatives [Member]
Derivative [Line Items]
Total derivatives, Asset	95,358	61,618
Total derivatives, Liability	4,504	8,944
Derivative Assets Offset In Balance Sheet	4,504	6,361
Derivative Liabilities Offset In Balance Sheet	4,504	6,361
Derivative Asset, Noncurrent	90,854
Derivative Liability, Noncurrent	0	2,583
Derivative Noncurrent [Member] | Not Designated As Hedging Instruments [Member] | Interest Rate Derivatives [Member]
Derivative [Line Items]
Total derivatives, Asset	15,493
Total derivatives, Liability	25,426	9,724
Derivative Assets Offset In Balance Sheet	15,493
Derivative Liabilities Offset In Balance Sheet	15,493	0
Derivative Asset, Noncurrent	0
Derivative Liability, Noncurrent	9,933	9,724
Derivative Current [Member] | Not Designated As Hedging Instruments [Member] | Commodity Price Derivatives [Member]
Derivative [Line Items]
Total derivatives, Asset	73,431	286,805
Total derivatives, Liability	19,350	21,102
Derivative Assets Offset In Balance Sheet	7,724	7,686
Derivative Liabilities Offset In Balance Sheet	7,724	7,686
Derivative Asset, Current	65,707
Derivative Liability, Current	11,626
Derivative Current [Member] | Not Designated As Hedging Instruments [Member] | Interest Rate Derivatives [Member]
Derivative [Line Items]
Total derivatives, Asset	9,530
Derivative Assets Offset In Balance Sheet	0
Derivative Asset, Current	$ 9,530