Fair Value (Details) (Recurring Basis [Member], USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Assets [Abstract]
Investments in common stock	$ 71	$ 78
NYMEX Fixed Price Derivative contracts	473	635
Total Assets	544	713
Liabilities [Abstract]
NYMEX Fixed Price Derivative contracts	7,460	7,030
Total Liabilities	7,460	7,030
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Assets [Abstract]
Investments in common stock	71	78
NYMEX Fixed Price Derivative contracts	0	0
Total Assets	71	78
Liabilities [Abstract]
NYMEX Fixed Price Derivative contracts	0	0
Total Liabilities	0	0
Significant Other Observable Inputs (Level 2) [Member]
Assets [Abstract]
Investments in common stock	0	0
NYMEX Fixed Price Derivative contracts	473	635
Total Assets	473	635
Liabilities [Abstract]
NYMEX Fixed Price Derivative contracts	7,460	7,030
Total Liabilities	7,460	7,030
Significant Unobservable Inputs (Level 3) [Member]
Assets [Abstract]
Investments in common stock	0	0
NYMEX Fixed Price Derivative contracts	0	0
Total Assets	0	0
Liabilities [Abstract]
NYMEX Fixed Price Derivative contracts	0	0
Total Liabilities	$ 0	$ 0