Derivative Instruments--Estimated Fair Value of Derivative Instruments (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014		Dec. 31, 2013
Derivatives, Fair Value [Line Items]
Derivative assets, gross	$ (251,863)		$ (13,113)
Derivative Asset, Netting adjustment	232	[1]	4,558	[1]
Current derivative assets, net	179,921		2,152
Long-term derivative assets, net	71,710		6,403
Derivative liabilities, Gross assets	(309)		(12,792)
Derivative Liability, Netting adjustment	(232)	[1]	(4,558)	[1]
Current derivative liabilities, net	(77)		(8,234)
Long-term derivative liabilities, net	0		0
Derivative assets (liabilities), gross	251,554		321
Current derivative assets (liabilities), net	179,844		(6,082)
Long-term derivative assets (liabilities), net	71,710		6,403
Swaps [Member] | Natural Gas Derivative [Member]
Derivatives, Fair Value [Line Items]
Derivative assets, gross	(32,939)		(1,457)
Derivative liabilities, Gross assets	0		(3,706)
Derivative assets (liabilities), gross	32,939		(2,249)
Swaps [Member] | Crude Oil Derivative [Member]
Derivatives, Fair Value [Line Items]
Derivative assets, gross	(23,465)		(112)
Derivative liabilities, Gross assets	0		(2,807)
Derivative assets (liabilities), gross	23,465		(2,695)
Costless Collars [Member] | Crude Oil Derivative [Member]
Derivatives, Fair Value [Line Items]
Derivative assets, gross	(1,175)		(2,776)
Derivative liabilities, Gross assets	0		(4)
Derivative assets (liabilities), gross	1,175		2,772
Enhanced Swap [Member] | Crude Oil Derivative [Member]
Derivatives, Fair Value [Line Items]
Derivative assets, gross	(100,724)		(6,988)
Derivative liabilities, Gross assets	0		(6,212)
Derivative assets (liabilities), gross	100,724		776
Put Options Purchased [Member] | Crude Oil Derivative [Member]
Derivatives, Fair Value [Line Items]
Derivative assets, gross	(93,268)		(74)
Derivative liabilities, Gross assets	0		0
Derivative assets (liabilities), gross	93,268		74
Basis Protection Swaps [Member] | Natural Gas Derivative [Member]
Derivatives, Fair Value [Line Items]
Derivative assets, gross	(292)		(1,706)
Derivative liabilities, Gross assets	(309)		(63)
Derivative assets (liabilities), gross	$ (17)		$ 1,643

[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.