Derivative Financial Instruments (Details 1) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011
Summary of location and aggregate fair value of all derivative financial instruments recorded in the consolidated balance sheets
Current assets: Derivative instruments	$ 16,033	$ 8,989
Current liabilities: Derivative instruments		171
Other assets: Derivative instruments	5,093	847
Long-term liabilities: Derivative instruments		383
Total Fair Value	21,126	9,282
Oil [Member]
Summary of location and aggregate fair value of all derivative financial instruments recorded in the consolidated balance sheets
Total Fair Value		(554)
Oil [Member] | Current liabilities [Member]
Summary of location and aggregate fair value of all derivative financial instruments recorded in the consolidated balance sheets
Current liabilities: Derivative instruments		(171)
Oil [Member] | Long-term liabilities [Member]
Summary of location and aggregate fair value of all derivative financial instruments recorded in the consolidated balance sheets
Long-term liabilities: Derivative instruments		(383)
Oil [Member] | Current Assets [Member]
Summary of location and aggregate fair value of all derivative financial instruments recorded in the consolidated balance sheets
Current assets: Derivative instruments	9,595
Oil [Member] | Other assets [Member]
Summary of location and aggregate fair value of all derivative financial instruments recorded in the consolidated balance sheets
Other assets: Derivative instruments	5,075
Natural Gas [Member] | Current Assets [Member]
Summary of location and aggregate fair value of all derivative financial instruments recorded in the consolidated balance sheets
Current assets: Derivative instruments	6,438	8,989
Natural Gas [Member] | Other assets [Member]
Summary of location and aggregate fair value of all derivative financial instruments recorded in the consolidated balance sheets
Other assets: Derivative instruments	$ 18	$ 847