Fair Value Measurements on a Recurring Basis (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2014		Dec. 31, 2013
Assets and liabilities measured at fair value on a recurring basis
Commodity derivatives assets, net	$ 3,280		$ 8,107
Commodity derivative liability, net	31,575		25,042
Fair Value, Inputs, Level 2
Assets and liabilities measured at fair value on a recurring basis
Commodity derivatives, gross asset	17,004		28,291
Commodity derivatives	45,299		45,226
Counterparty netting under agreements governing derivatives
Assets and liabilities measured at fair value on a recurring basis
Commodity derivatives assets, netting	(13,724)	[1]	(20,184)	[1]
Commodity derivatives liability, netting	$ (13,724)	[1]	$ (20,184)	[1]

[1] (1) Represents counterparty netting under agreements governing such derivatives.