Fair Value Measurements on a Recurring Basis Fair Value Measurements on a Recurring Basis (Details) - USD ($) $ in Thousands		Jun. 30, 2015	Dec. 31, 2014
Assets:
Commodity derivatives		$ 23,636	$ 60,843
Commodity derivatives	[1]	(7,126)	(17,149)
Commodity derivatives		16,510	43,694
Liabilities:
Commodity derivatives		11,047	17,149
Commodity derivatives	[1]	(7,126)	(17,149)
Commodity derivatives		$ 3,921	$ 0

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