Fair Value Measurements (Recurring Fair Value Measurements) (Details) (Commodity Derivatives [Member], USD $) In Thousands, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Gross Assets	$ 0	$ 1,998
Gross Liabilities	(16,165)	(7,044)
Derivative Asset	0	515
Derivative Liability	16,165	5,561
Financial liabilities	(16,165)	(5,046)
Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Gross Assets	0	1,978
Gross Liabilities	(10,084)	(4,429)
Financial liabilities	(10,084)	(2,451)
Level 3 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Gross Assets	0	20
Gross Liabilities	(6,081)	(2,615)
Financial liabilities	(6,081)	(2,595)
Effect of Netting [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Effect of netting on assets	0	(1,483)
Effect of netting on liabilities	0	1,483
Financial liabilities	$ 0	$ 0