Summary of Significant Accounting Policies, Derivatives by Hedging Relationship and Fair Value Measurements (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015	Dec. 31, 2015
Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivatives - Current assets	$ 221		$ 221		$ 0
Derivatives - Current liabilities	(292)		(292)		(195)
Net Value	(71)		(71)		(195)
Fair Value, Measurements, Recurring [Member] | Counterparty Offsets [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivatives - Current assets	(144)		(144)		0
Derivatives - Current liabilities	144		144		0
Net Value	0		0		0
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		0
Derivatives - Current liabilities	0		0		0
Net Value	0		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	365		365		0
Derivatives - Current liabilities	(436)		(436)		(195)
Net Value	(71)		(71)		(195)
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		0
Derivatives - Current liabilities	0		0		0
Net Value	0		0		$ 0
Commodity Contract [Member] | Revenues - Marketing [Member] | Not Designated as Hedging Instrument [Member]
Earnings (loss) recognized in income [Abstract]
Earnings	$ 282	$ 89	$ 124	$ 50