Fair Value Measurements--Derivatives Offset in the Consolidated Balance Sheets (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Fair Value Disclosures [Abstract]
Derivative, Net Liability Position, Aggregate Fair Value	$ 309
Offsetting Derivative Assets [Abstract]
Derivative assets, gross	251,863	13,113
Derivative assets, Offsetting assets (liabilities)	(232)	(4,558)
Derivative assets, net	251,631	8,555
Derivative assets, Derivatives		(3,484)	[1]
Derivative liabilities, Derivatives		3,484	[1]
Amounts outstanding under senior secured revolving credit facility	(118,430)	(4,211)
Derivative assets, Net amount	133,201	860
Derivative liabilities, Gross assets (liabilities)	(309)	(12,792)
Derivative liabilities, Offsetting assets (liabilities)	232	4,558
Derivative liabilities, Net assets (liabilities)	77	8,234
Derivative liabilities, Net amount	77	4,750
Total gross assets (liabilities)	251,554	321
Total offsetting assets (liabilities)	0	0
Total net assets (liabilities)	251,554	321
Total net amount	$ 133,124	$ (3,890)

[1] Since positive and negative positions with a counterparty are netted on the balance sheet only to the extent that they relate to the same current versus noncurrent classification, these represent remaining amounts that could have been offset under our master netting agreements.