Financial Instruments (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Fair Value of Financial Assets and Liabilities
Total assets
Total liabilities	59,219	33,892
Net assets (liabilities) at fair value	(59,219)	(33,892)
Level 1 [Member]
Fair Value of Financial Assets and Liabilities
Total assets	96	22
Total liabilities	59,315	33,914
Net assets (liabilities) at fair value	(59,219)	(33,892)
Netting [Member]
Fair Value of Financial Assets and Liabilities
Total assets	(96)	(22)
Total liabilities	(96)	(22)
Net assets (liabilities) at fair value
Commodity Derivatives [Member]
Fair Value of Financial Assets and Liabilities
Total assets
Total liabilities	566	1,034
Commodity Derivatives [Member] | Level 1 [Member]
Fair Value of Financial Assets and Liabilities
Total assets	96	22
Total liabilities	662	1,056
Commodity Derivatives [Member] | Netting [Member]
Fair Value of Financial Assets and Liabilities
Total assets	(96)	(22)
Total liabilities	(96)	(22)
Warrants [Member]
Fair Value of Financial Assets and Liabilities
Total liabilities	58,653	32,858
Warrants [Member] | Level 1 [Member]
Fair Value of Financial Assets and Liabilities
Total liabilities	58,653	32,858
Warrants [Member] | Netting [Member]
Fair Value of Financial Assets and Liabilities
Total liabilities	$ 0