Derivative Instruments--Effect of Derivative Instruments on the Consolidated Balance Sheets (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2014		Dec. 31, 2013
Fair value of derivative instruments
Derivative assets, gross	$ 1,564		$ 13,113
Current derivative assets, net	0		2,152
Long-term derivative assets, net	303		6,403
Derivative liabilities, gross	(65,236)		(12,792)
Current derivative liabilities, net	(46,818)		(8,234)
Long-term derivative liabilities, net	(17,157)		0
Derivative assets (liabilities), net	(63,672)		321
Current derivative assets (liabilities), net	(46,818)		(6,082)
Long-term derivative assets (liabilities), net	(16,854)		6,403
Derivative settlements receivable	0		4,616
Derivative settlements payable	8,674		377
Oil Derivative | Swaps
Fair value of derivative instruments
Derivative assets, gross	0		112
Derivative liabilities, gross	(4,232)		(2,807)
Derivative assets (liabilities), net	(4,232)		(2,695)
Oil Derivative | Costless Collars
Fair value of derivative instruments
Derivative assets, gross	75		2,776
Derivative liabilities, gross	(4,067)		(4)
Derivative assets (liabilities), net	(3,992)		2,772
Oil Derivative | Enhanced Swaps
Fair value of derivative instruments
Derivative assets, gross	0		6,988
Derivative liabilities, gross	(51,299)		(6,212)
Derivative assets (liabilities), net	(51,299)		776
Oil Derivative | Purchased Puts
Fair value of derivative instruments
Derivative assets, gross	339		74
Derivative liabilities, gross	0		0
Derivative assets (liabilities), net	339		74
Natural Gas Derivative | Swaps
Fair value of derivative instruments
Derivative assets, gross	1,129		1,457
Derivative liabilities, gross	(5,086)		(3,706)
Derivative assets (liabilities), net	(3,957)		(2,249)
Natural Gas Derivative | Basis Protection Swaps
Fair value of derivative instruments
Derivative assets, gross	21		1,706
Derivative liabilities, gross	(552)		(63)
Derivative assets (liabilities), net	(531)		1,643
Netting adjustments
Fair value of derivative instruments
Derivative assets, gross	(1,261)	[1]	(4,558)	[1]
Derivative liabilities, gross	1,261	[1]	4,558	[1]
Derivative assets (liabilities), net	$ 0	[1]	$ 0	[1]

[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.