Fair Value Measurements - Recurring Basis (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Noncurrent assets	$ 623	$ 5,439
Total asset	1,147	22,902
Total liabilities	(117,918)	(30,302)
Recurring
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Current assets	524	17,463
Noncurrent assets	623	5,439
Total asset	1,147	22,902
Current liabilities	(96,213)	(30,302)
Noncurrent derivative instruments	(21,705)
Total liabilities	(117,918)	(30,302)
Net derivative asset (liability)	(116,771)	(7,400)
Recurring | Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Current assets	(2,992)	(1,658)
Noncurrent assets	0	4,383
Total asset	(2,992)	2,725
Current liabilities	(95,999)	(28,414)
Noncurrent derivative instruments	(22,987)
Total liabilities	(118,986)	(28,414)
Net derivative asset (liability)	(121,978)	(25,689)
Recurring | Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Current assets	3,516	19,121
Noncurrent assets	623	1,056
Total asset	4,139	20,177
Current liabilities	(214)	(1,888)
Noncurrent derivative instruments	1,282
Total liabilities	1,068	(1,888)
Net derivative asset (liability)	$ 5,207	$ 18,289