A savings certificate entitling the Entity (that is, bearer) to receive interest at an established maturity date, based upon a fixed interest rate. A certificate of deposit may be issued in any denomination. Certificates of deposit are generally issued by commercial banks and, therefore, insured by the FDIC (up to the prescribed limit). Certificates of deposit generally restrict holders from withdrawing funds on demand without the incurrence of penalties. Generally, only certificates of deposit with original maturities of three months or less qualify as cash equivalents. Original maturity means original maturity to the entity holding the investment. As a related example, both a three-month US Treasury bill and a three-year Treasury note purchased three months from maturity qualify as cash equivalents. However, a Treasury note purchased three-years ago does not become a cash equivalent when its remaining maturity is three months.

+ References+ Details

Fair values as of the balance sheet date of the net amount of all assets and liabilities resulting from contracts that meet the criteria of being accounted for as derivative instruments.

+ References+ Details

Fair Value Measurements (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Assets (Liabilities)
Certificates of deposit	$ 230	$ 1,335
Oil, natural gas and NGL derivatives	4,479	9,282
Fair value on a recurring basis [Member]
Assets (Liabilities)
Certificates of deposit	230	1,335
Oil, natural gas and NGL derivatives		9,836
Total	4,709	10,617
Fair value on a recurring basis [Member] \| Oil [Member]
Assets (Liabilities)
Oil, natural gas and NGL derivatives	(670)
Fair value on a recurring basis [Member] \| Natural Gas [Member]
Assets (Liabilities)
Oil, natural gas and NGL derivatives	5,149
Fair value on a recurring basis [Member] \| Level 1 [Member]
Assets (Liabilities)
Certificates of deposit
Total
Fair value on a recurring basis [Member] \| Level 1 [Member] \| Oil [Member]
Assets (Liabilities)
Oil, natural gas and NGL derivatives
Fair value on a recurring basis [Member] \| Level 1 [Member] \| Natural Gas [Member]
Assets (Liabilities)
Oil, natural gas and NGL derivatives
Fair value on a recurring basis [Member] \| Level 2 [Member]
Assets (Liabilities)
Certificates of deposit	230	1,335
Total	4,709	10,617
Fair value on a recurring basis [Member] \| Level 2 [Member] \| Oil [Member]
Assets (Liabilities)
Oil, natural gas and NGL derivatives	(670)	(554)
Fair value on a recurring basis [Member] \| Level 2 [Member] \| Natural Gas [Member]
Assets (Liabilities)
Oil, natural gas and NGL derivatives	5,149	9,836
Fair value on a recurring basis [Member] \| Level 3 [Member]
Assets (Liabilities)
Certificates of deposit
Total
Fair value on a recurring basis [Member] \| Level 3 [Member] \| Oil [Member]
Assets (Liabilities)
Oil, natural gas and NGL derivatives
Fair value on a recurring basis [Member] \| Level 3 [Member] \| Natural Gas [Member]
Assets (Liabilities)
Oil, natural gas and NGL derivatives