Financial Instruments (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013		Dec. 31, 2012
Fair Value of Financial Assets and Liabilities
Total assets	$ 261
Total liabilities	41,810		33,892
Net assets (liabilities) at fair value	(41,549)		(33,892)
Level 1 [Member]
Fair Value of Financial Assets and Liabilities
Total assets	315		22
Total liabilities	41,864		33,914
Net assets (liabilities) at fair value	(41,549)		(33,892)
Netting [Member]
Fair Value of Financial Assets and Liabilities
Total assets	(54)	[1]	(22)	[1]
Total liabilities	(54)	[1]	(22)	[1]
Net assets (liabilities) at fair value		[1]		[1]
Commodity Derivatives [Member]
Fair Value of Financial Assets and Liabilities
Total assets	261
Total liabilities			1,034
Commodity Derivatives [Member] | Level 1 [Member]
Fair Value of Financial Assets and Liabilities
Total assets	315		22
Total liabilities	54		1,056
Commodity Derivatives [Member] | Netting [Member]
Fair Value of Financial Assets and Liabilities
Total assets	(54)	[1]	(22)	[1]
Total liabilities	(54)	[1]	(22)	[1]
Warrants [Member]
Fair Value of Financial Assets and Liabilities
Total liabilities	41,810		32,858
Warrants [Member] | Level 1 [Member]
Fair Value of Financial Assets and Liabilities
Total liabilities	41,810		32,858
Warrants [Member] | Netting [Member]
Fair Value of Financial Assets and Liabilities
Total liabilities		[1]		[1]

[1] *Relates primarily to exchange traded futures. Gain and loss positions on multiple contracts are settled net on a daily basis with the exchange.