Derivative Activities (Details Textuals) (USD $)	3 Months Ended		9 Months Ended								9 Months Ended			6 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011 Year FinancialInstitution CreditFacility Project Well CommercialBank	Sep. 30, 2010	Dec. 31, 2010	Sep. 30, 2011 Natural Gas [Member] Bcf MMBtu	Sep. 30, 2011 NGL [Member] MMbbl PerBarrel	Sep. 30, 2011 Collar Oil [Member] PerBarrel MMbbl	Sep. 30, 2011 Collars of Gas [Member] MMBtu Bcf	Sep. 30, 2011 Call Option of Oil[ Member] MMbbl	Sep. 30, 2011 2011 [Member]	Sep. 30, 2011 2012 [Member]	Sep. 30, 2011 2013 [Member]	Jun. 30, 2011 Barnett Shale Properties [Member]	Sep. 30, 2011 Barnett Shale Properties [Member]
Derivative [Line Items]
Nonmonetary notional amount of price risk derivatives						25,600,000	2,500,000	700,000	159,800,000	2,200,000
Average floor price								70.00	5.24
Average cap price								80.00	5.87
Average price of SWAP per mcf						5.00	103.00
Unrealized pre-tax derivative gain expected to be reclassified into earnings											37,900,000	73,800,000	26,200,000
Loss on derivative contracts														(1,700,000)
Accumulated other comprehensive income (loss)	86,209,000		86,209,000		67,470,000										9,400,000
Average price of oil call option (per barrel)										83.86
Derivative Activities (Textuals) [Abstract]
Derivative assets liabilities at fair value net	183,600,000		183,600,000
Unrealized pre-tax derivative gain			137,900,000
Gains (Losses) in oil and gas sales related to settled hedging transactions	26,800,000	15,600,000	80,700,000	35,200,000
Ineffective unrealized and realized gains (losses) recognized income	(1,935,000)	2,389,000	7,089,000	2,048,000
Gains/losses recorded due to the discontinuance of hedge accounting treatment			$ 0	$ 0
Number of financial institutions with whom we conduct derivative activities			10
Number of secured financial institutions with whom we conduct derivative activities			9