Derivative Instruments--Estimated Fair Value of Derivative Instruments (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Jun. 30, 2013	Dec. 31, 2013		Dec. 31, 2012
Derivatives, Fair Value [Line Items]
Derivative assets, gross		$ (13,113)		$ (46,010)
Current derivative assets, net		2,152		42,516
Long-term derivative assets, net		6,403		517
Derivative liabilities, gross		(12,792)		(5,605)
Current derivative liabilities, net		(8,234)		(436)
Long-term derivative liabilities, net		0		(2,192)
Derivative assets (liabilities), net		321		40,405
Current derivative assets (liabilities), net		(6,082)		42,080
Long-term derivative assets (liabilities), net		6,403		(1,675)
Netting adjustments
Derivatives, Fair Value [Line Items]
Derivative assets, gross		4,558	[1]	2,977	[1]
Derivative liabilities, gross		4,558	[1]	2,977	[1]
Swaps | Crude Oil Derivative
Derivatives, Fair Value [Line Items]
Derivative assets, gross		(112)		(4,957)
Derivative liabilities, gross		(2,807)		(1,339)
Derivative assets (liabilities), net		(2,695)		3,618
Swaps | Natural Gas Derivative
Derivatives, Fair Value [Line Items]
Derivative assets, gross		(1,457)		(13,642)
Derivative liabilities, gross		(3,706)		(1,487)
Derivative assets (liabilities), net		(2,249)		12,155
Costless Collars | Crude Oil Derivative
Derivatives, Fair Value [Line Items]
Derivative assets, gross		(2,776)		(27,411)
Derivative liabilities, gross		(4)		(1,180)
Derivative assets (liabilities), net		2,772		26,231
Enhanced Swap | Crude Oil Derivative
Derivatives, Fair Value [Line Items]
Derivative assets, gross		(6,988)
Derivative liabilities, gross		(6,212)
Derivative assets (liabilities), net		776		0
Put Options Purchased | Crude Oil Derivative
Derivatives, Fair Value [Line Items]
Derivative assets, gross		(74)	[2]
Derivative liabilities, gross		0	[2]
Derivative assets (liabilities), net		74	[2]	0	[2]
Premium Paid For Put Options On Commodity Derivative Contracts	664
Basis Protection Swaps | Natural Gas Derivative
Derivatives, Fair Value [Line Items]
Derivative assets, gross		(1,706)		0
Derivative liabilities, gross		(63)		(1,599)
Derivative assets (liabilities), net		$ 1,643		$ (1,599)

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

[2] Includes premiums of $664 paid during the second quarter of 2013. No additional premiums have been paid.