Fair Value Measurements (Details) (USD $)	Dec. 31, 2013	Dec. 31, 2012
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value amount of transfers in or out of Levels 1 or 2	$ 0	$ 0
Level 2 [Member] | Portion at Fair Value Measurement [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative current assets, gross amount recognized	2,389,000	24,014,000
Derivative current assets, gross amounts offset in the consolidated balance sheets	(2,389,000)	(33,000)
Derivative current assets, net amounts presented in the consolidated balance sheets	0	23,981,000
Derivative non-current assets, gross amount recognized	11,709,000	6,778,000
Derivative non-current assets, gross amounts offset in the consolidated balance sheets	(2,425,000)	(1,598,000)
Derivative non-current assets, net amounts presented in the consolidated balance sheets	9,284,000	5,180,000
Derivative current liabilities, gross amount recognized	(12,336,000)	(33,000)
Derivative current liabilities, gross amounts offset in the consolidated balance sheets	2,389,000	33,000
Derivative current liabilities, net amounts presented in the consolidated balance sheets	(9,947,000)	0
Derivative non-current liabilities, gross amount recognized	(2,613,000)	(1,598,000)
Derivative non-current liabilities, gross amounts offset in the consolidated balance sheets	2,425,000	1,598,000
Derivative non-current liabilities, net amounts presented in the consolidated balance sheets	(188,000)	0
Derivative asset (liabilities), gross amount recognized	(851,000)	29,161,000
Derivative liabilities (assets), gross amounts offset in the consolidated balance sheets	0	0
Total, net amounts presented in the consolidated balance sheets	$ (851,000)	$ 29,161,000