Derivative Instruments and Hedging Activities (Details Textual) (USD $) In Thousands, unless otherwise specified	12 Months Ended				12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Mar. 06, 2009	Mar. 03, 2009	Dec. 31, 2011 Oil [Member]	Dec. 31, 2010 Oil [Member]	Dec. 31, 2009 Oil [Member]	Dec. 31, 2011 Natural Gas [Member]	Dec. 31, 2010 Natural Gas [Member]	Dec. 31, 2009 Natural Gas [Member]	Mar. 06, 2009 Natural Gas [Member] Contract
Derivative Instruments, Gain (Loss) Recognized in Income, Net [Abstract]
Increase in oil revenue owing to effective hedging contracts								$ 19,432	$ 38,678	$ 101,429
Decrease/Increase in oil revenue owing to effective hedging contracts					(32,706)	(29,047)	61,747
Number of contract unwound											2
Derivative Instruments and Hedging Activities (Textual) [Abstract]
Maximum correlation between price of oil & natural gas in market and underlying price basis indicative in the derivative contract		100.00%
Proceeds from unwounding of natural gas hedges			53,814
Proceeds from unwounding existing crude oil hedges				59,007
Accumulated other comprehensive loss, net of tax	21,868	(14,204)
Accumulated other comprehensive loss, to be reclassified into earning in the next twelve months	$ 7,303