Financial Instruments and Concentrations of Risk (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012		Dec. 31, 2011
Fair Value of Financial Assets and Liabilities
Total assets	$ 0		$ 162
Total liabilities	33,892		12,538
Net assets (liabilities) at fair value	(33,892)		(12,376)
Level 1 [Member]
Fair Value of Financial Assets and Liabilities
Total assets	22		393
Total liabilities	33,914		12,411
Net assets (liabilities) at fair value	(33,892)		(12,018)
Level 2 [Member]
Fair Value of Financial Assets and Liabilities
Total assets	0		0
Total liabilities	0		358
Net assets (liabilities) at fair value	0		(358)
Level 3 [Member]
Fair Value of Financial Assets and Liabilities
Total assets	0		0
Total liabilities	0		0
Net assets (liabilities) at fair value	0		0
Netting [Member]
Fair Value of Financial Assets and Liabilities
Total assets	(22)	[1]	(231)	[1]
Total liabilities	(22)	[1]	(231)	[1]
Net assets (liabilities) at fair value	0	[1]	0	[1]
Commodity Derivatives [Member]
Fair Value of Financial Assets and Liabilities
Total assets	0		162
Total liabilities	1,034		0
Commodity Derivatives [Member] | Level 1 [Member]
Fair Value of Financial Assets and Liabilities
Total assets	22		393
Total liabilities	1,056		231
Commodity Derivatives [Member] | Level 2 [Member]
Fair Value of Financial Assets and Liabilities
Total assets	0		0
Total liabilities	0		0
Commodity Derivatives [Member] | Level 3 [Member]
Fair Value of Financial Assets and Liabilities
Total assets	0		0
Total liabilities	0		0
Commodity Derivatives [Member] | Netting [Member]
Fair Value of Financial Assets and Liabilities
Total assets	(22)	[1]	(231)	[1]
Total liabilities	(22)	[1]	(231)	[1]
Warrants [Member]
Fair Value of Financial Assets and Liabilities
Total liabilities	32,858		12,180
Warrants [Member] | Level 1 [Member]
Fair Value of Financial Assets and Liabilities
Total liabilities	32,858		12,180
Warrants [Member] | Level 2 [Member]
Fair Value of Financial Assets and Liabilities
Total liabilities	0		0
Warrants [Member] | Level 3 [Member]
Fair Value of Financial Assets and Liabilities
Total liabilities	0		0
Warrants [Member] | Netting [Member]
Fair Value of Financial Assets and Liabilities
Total liabilities	0	[1]	0	[1]
Interest Rate Swap [Member]
Fair Value of Financial Assets and Liabilities
Total liabilities	0		358
Interest Rate Swap [Member] | Level 1 [Member]
Fair Value of Financial Assets and Liabilities
Total liabilities			0
Interest Rate Swap [Member] | Level 2 [Member]
Fair Value of Financial Assets and Liabilities
Total liabilities	0		358
Interest Rate Swap [Member] | Level 3 [Member]
Fair Value of Financial Assets and Liabilities
Total liabilities	0		0
Interest Rate Swap [Member] | Netting [Member]
Fair Value of Financial Assets and Liabilities
Total liabilities	$ 0	[1]	$ 0	[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.