Derivative Financial Instruments (Derivatives and Hedging - Designated) (Details) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	$ 4,930	$ 5,717
Derivative Liability, Fair Value, Gross Liability	10,951	653
Designated as Hedging Instrument [Member] | NYMEX Commodity Contracts [Member] | Other Current Assets [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	99	60
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	4,831	3,478
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	2,179
Designated as Hedging Instrument [Member] | Interest Rate Contract [Member] | Other Current Liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative Liability, Fair Value, Gross Liability	10,951	653
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	19,151	44,829
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	$ 1,489	$ 5,646