Derivative Financial Instruments (Narrative) (Details) (USD $) In Millions, unless otherwise specified	1 Months Ended	3 Months Ended		1 Months Ended			3 Months Ended		1 Months Ended	3 Months Ended		1 Months Ended	3 Months Ended		1 Months Ended	3 Months Ended		1 Months Ended	3 Months Ended		6 Months Ended	3 Months Ended	1 Months Ended		3 Months Ended			1 Months Ended
	Apr. 30, 2012	Jun. 30, 2012	Dec. 31, 2011	Aug. 03, 2012 2015 Gas Derivatives [Member] [Member]	Aug. 03, 2012 2014 Gas Derivatives [Member]	Aug. 03, 2012 2012 Swap Contracts [Member] bbl	Jun. 30, 2012 2012 Swap Contracts [Member] bbl MMBTU		Aug. 03, 2012 2014 - Collar Contracts With Short Puts [Member] bbl	Jun. 30, 2012 2014 - Collar Contracts With Short Puts [Member] MMBTU bbl		Aug. 03, 2012 2014 - Collar Contracts With Short Puts [Member] Ceiling [Member]	Jun. 30, 2012 2014 - Collar Contracts With Short Puts [Member] Ceiling [Member]		Aug. 03, 2012 2014 - Collar Contracts With Short Puts [Member] Floor [Member]	Jun. 30, 2012 2014 - Collar Contracts With Short Puts [Member] Floor [Member]		Aug. 03, 2012 2014 - Collar Contracts With Short Puts [Member] Short Put [Member]	Jun. 30, 2012 2014 - Collar Contracts With Short Puts [Member] Short Put [Member]		Jun. 30, 2012 Rollfactor Swap Contracts [Member]	Jun. 30, 2012 2013 Diesel Swaps [Member] bbl	Aug. 03, 2012 2012 Interest Rate Derivatives [Member]	Aug. 03, 2012 NGL Swap [Member] bbl	Jun. 30, 2012 NGL Swap [Member] bbl	Jun. 30, 2012 NGL Collar Contracts With Short Put [Member] bbl	Jun. 30, 2012 NGL Collar Contracts With Short Put [Member] Short Put [Member]	Aug. 03, 2012 2015 Gas Collars with Short Puts Derivatives [Member] MMBTU	Aug. 03, 2012 2015 Gas Collars with Short Puts Derivatives [Member] Ceiling [Member]	Aug. 03, 2012 2015 Gas Collars with Short Puts Derivatives [Member] Floor [Member]	Aug. 03, 2012 2015 Gas Collars with Short Puts Derivatives [Member] Short Put [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Volume (Bbl)						8,000	3,000	[1]	5,000	40,000
Average Daily Oil Production Derivative Price Per Barrel						93.09	79.32					102.22	122.77		95.00	91.50		80.00	74.88
NYMEX swap multiple, second nearby month																					0.6667
NYMEX swap multiple, third nearby month																					0.3333
Terminated Derivatives Proceeds				$ 19.4	$ 47.1																		$ 28.4					$ 4.7
Derivative Nonmonetary Notional Volume per Day (BBL)																						250		2,000	750	3,000
Derivative, Average Cap Price (per BBL)																										79.99
Derivative, Average Floor Price (per BBL)																										67.70
Derivative, Nonmonetary Notional Amount, Price (per BBL)																											55.76
Average fixed price (per BBL)																						111.30		80.06	35.03
Derivative, Fixed Interest Rate	3.21%	3.06%
Notional amount of debt	250	200
Net deferred losses from hedging in AOCI			(3.2)
Net deferred gains or losses associated to net deferred tax benefits			1.8
Derivative Instruments Loss From Discontinued Interest Rate Hedges In Aoci			$ 1.7
Average Daily Gas Production Derivatives Volume (MMBTU)							275,000			30,000	[2]																	30,000
Average Daily Gas Production Derivatives Price Per MMBtu							4.97						7.66	[2]		5.67	[2]		4.33	[2]									7.11	5.00	4.00

[1] Subsequent to June 30, 2012, the Company entered into additional NYMEX (i) swap contracts for 8,000 BBLs per day of August 2012 through December 2012 production with a price of $93.09 per BBL and (ii) collar contracts with short puts for 5,000 BBLs per day of 2014 production with a ceiling price of $102.22 per BBL, a floor price of $95.00 per BBL and a short put price of $80.00 per BBL.

[2] Subsequent to June 30, 2012, the Company (i) terminated its 2014 gas derivative positions, including basis swaps, for net proceeds of $47.1 million, (ii) terminated its 2015 collar contracts for proceeds of $19.4 million and (iii) terminated 2015 collar contracts with short puts for 30,000 MMBTU per day with a ceiling price of $7.11 per MMBTU, a floor price of $5.00 per MMBTU and a short put price of $4.00 per MMBTU for proceeds of $4.7 million.