Fair Value Measurements (Recurring Fair Value Measurements) (Details) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Asset	$ 177	$ 11,154
Derivative Liability	5,817	285
Commodity Derivatives [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Asset	177	11,154
Derivative Liability	5,817	285
Financial assets (liabilities)	(5,640)	10,869
Commodity Derivatives [Member] | Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Gross Assets	1,206	2,794
Gross Liabilities	(4,719)	(1,019)
Financial assets (liabilities)	(3,513)	1,775
Commodity Derivatives [Member] | Level 3 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Gross Assets	714	10,145
Gross Liabilities	(2,841)	(1,051)
Financial assets (liabilities)	(2,127)	9,094
Commodity Derivatives [Member] | Effect of Netting [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Effect of netting on assets	(1,743)	(1,785)
Effect of netting on liabilities	1,743	1,785
Financial assets (liabilities)	$ 0	$ 0