Fair Value Measurements--Recurring Fair Value Measurements (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		12 Months Ended
	Mar. 31, 2014		Dec. 31, 2013
Fair Value Disclosures [Abstract]
Rate reflecting our nonperformance risk	2.00%		1.75%
Weighted-average rate reflecting our counterparties' nonperformance risk	0.25%		0.31%
Fair Value Hierarchy for Financial Instruments Measured at Fair Value on a Recurring Basis [Line Items]
Derivative assets, gross	$ 3,100		$ 13,113
Derivative liabilities, gross	(23,223)		(12,792)
Derivative assets (liabilities), net	(20,123)		321
Netting adjustments
Fair Value Hierarchy for Financial Instruments Measured at Fair Value on a Recurring Basis [Line Items]
Derivative assets, gross	(253)	[1]	(4,558)	[1]
Derivative liabilities, gross	253	[1]	4,558	[1]
Derivative assets (liabilities), net	0	[1]	0	[1]
Recurring Fair Value Measurements
Fair Value Hierarchy for Financial Instruments Measured at Fair Value on a Recurring Basis [Line Items]
Derivative assets, net	2,847		8,555
Derivative liabilities, net	(22,970)		(8,234)
Derivative assets (liabilities), net	(20,123)		321
Recurring Fair Value Measurements | Significant other observable inputs (Level 2)
Fair Value Hierarchy for Financial Instruments Measured at Fair Value on a Recurring Basis [Line Items]
Derivative assets, gross	736		3,275
Derivative liabilities, gross	(11,091)		(6,576)
Derivative assets (liabilities), net	(10,355)		(3,301)
Recurring Fair Value Measurements | Significant unobservable inputs (Level 3)
Fair Value Hierarchy for Financial Instruments Measured at Fair Value on a Recurring Basis [Line Items]
Derivative assets, gross	2,364		9,838
Derivative liabilities, gross	(12,132)		(6,216)
Derivative assets (liabilities), net	(9,768)		3,622
Recurring Fair Value Measurements | Netting adjustments
Fair Value Hierarchy for Financial Instruments Measured at Fair Value on a Recurring Basis [Line Items]
Derivative assets, gross	(253)	[2]	(4,558)	[2]
Derivative liabilities, gross	253	[2]	4,558	[2]
Derivative assets (liabilities), net	$ 0	[2]	$ 0	[2]

[1] Amounts represent the impact of master netting agreements that allow us to net settle positive and negative positions with the same counterparty. Positive and negative positions with a counterparty are netted only to the extent that they relate to the same current versus noncurrent classification on the balance sheet.

[2] Amounts represent the impact of master netting agreements that allow us to net settle positive and negative positions with the same counterparty.