Fair Value Measurements (Recurring Fair Value Measurements) (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Gross Assets	$ 0	$ 1,998
Gross Liabilities	(14,540)	(7,044)
Financial assets (liabilities)	(14,540)	(5,046)
Commodity Derivatives [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets	0	515
Liabilities	(14,540)	(5,561)
Commodity Derivatives [Member] | Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Gross Assets	0	1,978
Gross Liabilities	(10,076)	(4,429)
Financial assets (liabilities)	(10,076)	(2,451)
Commodity Derivatives [Member] | Level 3 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Gross Assets	0	20
Gross Liabilities	(4,464)	(2,615)
Financial assets (liabilities)	(4,464)	(2,595)
Commodity Derivatives [Member] | 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 assets (liabilities)	$ 0	$ 0