Summary of Significant Accounting Policies, Derivatives by Hedging Relationship and Fair Value Measurements (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014
Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivatives - Current assets	$ 806		$ 936
Derivatives - Current liabilities	(852)		(943)
Net Value	(46)		(7)
Fair Value, Measurements, Recurring [Member] | Level 1 Quoted Prices [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivatives - Current assets	0		0
Derivatives - Current liabilities	0		0
Net Value	0		0
Fair Value, Measurements, Recurring [Member] | Level 2 Observable [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivatives - Current assets	871		1,332
Derivatives - Current liabilities	(917)		(1,339)
Net Value	(46)		(7)
Fair Value, Measurements, Recurring [Member] | Level 3 Unobservable [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivatives - Current assets	0		0
Derivatives - Current liabilities	0		0
Net Value	0		0
Fair Value, Measurements, Recurring [Member] | Counterparty Offsets [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivatives - Current assets	(65)		(396)
Derivatives - Current liabilities	65		396
Net Value	0		0
Commodity Contract [Member] | Revenues - Marketing [Member] | Not Designated as Hedging Instrument [Member]
Earnings (loss) recognized in income [Abstract]
Earnings (Loss)	$ (39)	$ 398