Fair Value Measurements (Recurring Fair Value Measurements) (Details) - Commodity Derivatives [Member] - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Gross Assets	$ 14,790	$ 31,139
Gross Liabilities	(66)	0
Derivative Asset	14,724	31,139
Derivative Liability	0	0
Financial assets (liabilities)	14,724	31,139
Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Gross Assets	14,517	27,784
Gross Liabilities	0	0
Financial assets (liabilities)	14,517	27,784
Level 3 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Gross Assets	273	3,355
Gross Liabilities	(66)	0
Financial assets (liabilities)	207	3,355
Effect of Netting [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Effect of netting on assets	(66)	0
Effect of netting on liabilities	66	0
Financial assets (liabilities)	$ 0	$ 0