Fair Value Measurements (Recurring Fair Value Measurements) (Details) - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Asset	$ 0	$ 11,154
Derivative Liability	13,066	285
Commodity Derivatives [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Asset	0	11,154
Derivative Liability	13,066	285
Financial assets (liabilities)	(13,066)	10,869
Commodity Derivatives [Member] | Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Gross Assets	435	2,794
Gross Liabilities	(8,740)	(1,019)
Financial assets (liabilities)	(8,305)	1,775
Commodity Derivatives [Member] | Level 3 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Gross Assets	515	10,145
Gross Liabilities	(5,276)	(1,051)
Financial assets (liabilities)	(4,761)	9,094
Commodity Derivatives [Member] | Effect of Netting [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Effect of netting on assets	(950)	(1,785)
Effect of netting on liabilities	950	1,785
Financial assets (liabilities)	$ 0	$ 0