Derivative Financial Instruments (Derivatives and Hedging - Designated) (Details) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	$ 25,986	$ 14,764
Derivative Liability, Fair Value, Gross Liability	1,082	26,478
Designated as Hedging Instrument [Member] | NYMEX Commodity Contracts [Member] | Other Current Assets [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	913	360
Designated as Hedging Instrument [Member] | NYMEX Commodity Contracts [Member] | Other Current Liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative Liability, Fair Value, Gross Liability	0	0
Designated as Hedging Instrument [Member] | NYMEX Commodity Contracts [Member] | Other Noncurrent Assets [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	24,499	14,404
Designated as Hedging Instrument [Member] | NYMEX Commodity Contracts [Member] | Other Noncurrent Liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative Liability, Fair Value, Gross Liability	0	0
Designated as Hedging Instrument [Member] | Interest Rate Contract [Member] | Other Current Assets [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset		0
Designated as Hedging Instrument [Member] | Interest Rate Contract [Member] | Other Current Liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative Liability, Fair Value, Gross Liability		26,478
Designated as Hedging Instrument [Member] | Interest Rate Contract [Member] | Other Noncurrent Assets [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	574
Designated as Hedging Instrument [Member] | Interest Rate Contract [Member] | Other Noncurrent Liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative Liability, Fair Value, Gross Liability	1,082
Not Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	63,726
Derivative Liability, Fair Value, Gross Liability	10,695
Not Designated as Hedging Instrument [Member] | NYMEX Commodity Contracts [Member] | Other Current Assets [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	58,685	92,000
Not Designated as Hedging Instrument [Member] | NYMEX Commodity Contracts [Member] | Other Current Liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative Liability, Fair Value, Gross Liability	10,426	$ 10,622
Not Designated as Hedging Instrument [Member] | NYMEX Commodity Contracts [Member] | Other Noncurrent Assets [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	5,041
Not Designated as Hedging Instrument [Member] | NYMEX Commodity Contracts [Member] | Other Noncurrent Liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative Liability, Fair Value, Gross Liability	$ 269